2024 Full Moon calendar: Dates, times, types, and names

The phenomenon of a Full Moon arises when our planet, Earth, is precisely sandwiched between the Sun and the Moon. This alignment ensures the entire side of the Moon that faces us gleams under sunlight. Thanks to the Moon’s orbit around Earth, the angle of sunlight hitting the lunar surface and being reflected back to our planet changes. That creates different lunar phases.

We’ll update this article multiple times each week with the latest moonrise, moonset, Full Moon schedule, and some of what you can see in the sky each week.

The Full Moon in May 2024 is the Flower Moon and that will happen at 9:53 a.m. EDT on Thursday, May 23.

Here’s the complete list of Full Moons this year and their traditional names.

2024 Full Moon schedule and names of each

(all times Eastern)

  • Jan. 25 — 12:54 p.m. — Wolf Moon
  • Feb. 24 —7:30 a.m. — Snow Moon
  • March 25 — 3 a.m. — Worm Moon
  • April 23 — 7:49 p.m. — Pink Moon
  • Full Moon on May 23 — 9:53 a.m. — Flower Moon 🌷
  • June 21 — 9:08 p.m. — Strawberry Moon
  • July 21 — 6:17 a.m. — Buck Moon
  • Aug. 19 — 2:26 p.m. — Sturgeon Moon
  • Sept. 17 — 10:34 p.m. — Corn Moon
  • Oct. 17 — 7:26 a.m. — Hunter’s Moon
  • Nov. 15 — 4:28 p.m. — Beaver Moon
  • Dec. 15 — 4:02 a.m. — Cold Moon

The phases of the Moon in May 2024

The images below show the day-by-day phases of the Moon this month. The Full Moon in May is at 9:53 a.m. ET on Thursday, May 23, and is called the Flower Moon.

These images show the day-by-day phases of the moon this month. The Full Moon in May is at 9:53 a.m. ET on Thursday, May 23, and is called the Flower moon.

The moonrise and moonset schedule this week

The following is adapted from Alison Klesman’s The Sky This Week article, which you can find here.

*Times for sunrise, sunset, moonrise, and moonset are given in local time from 40° N 90° W. The Moon’s illumination is given at 12 P.M. local time from the same location.

Saturday, May 18

Sunrise: 5:42 A.M.
Sunset: 8:12 P.M.
Moonrise: 3:37 P.M.
Moonset: 3:18 A.M.
Moon Phase: Waxing gibbous (79%)

Sunday, May 19

Sunrise: 5:41 A.M.
Sunset: 8:13 P.M.
Moonrise: 4:36 P.M.
Moonset: 3:37 A.M.
Moon Phase: Waxing gibbous (86%)

Monday, May 20

Sunrise: 5:40 A.M.
Sunset: 8:13 P.M.
Moonrise: 5:38 P.M.
Moonset: 3:57 A.M.
Moon Phase: Waxing gibbous (92%)

Tuesday, May 21

Sunrise: 5:40 A.M.
Sunset: 8:14 P.M.
Moonrise: 6:42 P.M.
Moonset: 4:19 A.M.
Moon Phase: Waxing gibbous (96%)

Wednesday, May 22

Sunrise: 5:39 A.M.
Sunset: 8:15 P.M.
Moonrise: 7:49 P.M.
Moonset: 4:45 A.M.
Moon Phase: Waxing gibbous (99%)

Thursday, May 23
Full Moon occurs this morning 9:53 A.M. EDT. May’s Full Moon is also called the Flower Moon, and you’ll want to catch it later this evening when our satellite passes just 0.4° north of the brilliant red giant Antares at 11 P.M. EDT. The event is readily visible in the eastern half of the U.S., though those farther west may have to wait an hour or two for the pair to rise high enough in the sky for viewing.

If the Moon is above your horizon by 11 P.M. EDT, look southwest to spot it just below Antares, Scorpius’ 1st-magnitude alpha star. Plus, there’s a bonus — a second occultation for portions of the U.S. this week. Observers in the southeastern region of the country will now see the Moon occult Antares, passing in front of the star between about 9 P.M. and 10 P.M. EDT — again, check IOTA’s webpage for the event to see if your location falls within the viewing area and find out when you will see the star disappear and reappear.

Antares is a red giant in the later stages of its life — although it has swelled in size, its temperature has dropped, which is what gives the star its reddish hue. It’s so bright and so red that it is often mistaken for our own Red Planet, Mars. If you want to compare the two, you’ll need to wait several hours, until about 4:15 A.M. local daylight time tomorrow morning — that’s when Mars will rise more than 5° above the eastern horizon and you can see whether you think its brightness and hue match that of Antares, now in the southwest and well clear of the Moon!

Sunrise: 5:38 A.M.
Sunset: 8:16 P.M.
Moonrise: 8:57 P.M.
Moonset: 5:18 A.M.
Moon Phase: Full

Friday, May 24

Sunrise: 5:37 A.M.
Sunset: 8:17 P.M.
Moonrise: 10:03 P.M.
Moonset: 5:58 A.M.
Moon Phase: Waning gibbous (98%)

The phases of the Moon

The phases of the Moon are: New Moon, waxing crescent, First Quarter, waxing gibbous, Full Moon, waning gibbous, Last Quarter, and waning crescent. A cycle starting from one Full Moon to its next counterpart, termed the synodic month or lunar month, lasts about 29.5 days.

Though a Full Moon only occurs during the exact moment when Earth, Moon, and Sun form a perfect alignment, to our eyes, the Moon seems Full for around three days.

Different names for different types of Full Moon

There are a wide variety of specialized names used to identify distinct types or timings of Full Moons. These names primarily trace back to a blend of cultural, agricultural, and natural observations about the Moon, aimed at allowing humans to not only predict seasonal changes, but also track the passage of time. 

For instance, almost every month’s Full Moon boasts a name sourced from Native American, Colonial American, or other North American traditions, with their titles mirroring seasonal shifts and nature’s events.

A composite of each month’s Full Moon in 2020 and 2021. Credit: Soumyadeep Mukherjee

Wolf Moon (January): Inspired by the cries of hungry wolves.

Snow Moon (February): A nod to the month’s often heavy snowfall.

Worm Moon (March): Named after the earthworms that signal thawing grounds.

Pink Moon (April): In honor of the blossoming pink wildflowers.

Flower Moon (May): Celebrating the bloom of flowers.

Strawberry Moon (June): Marks the prime strawberry harvest season.

Buck Moon (July): Recognizing the new antlers on bucks.

Sturgeon Moon (August): Named after the abundant sturgeon fish.

Corn Moon (September): Signifying the corn harvesting period.

Hunter’s Moon (October): Commemorating the hunting season preceding winter.

Beaver Moon (November): Reflects the time when beavers are busy building their winter dams.

Cold Moon (December): Evocative of winter’s chill.

In addition, there are a few additional names for Full Moons that commonly make their way into public conversations and news.

Super Moon: This term is reserved for a Full Moon that aligns with the lunar perigee, which is the Moon’s nearest point to Earth in its orbit. This proximity renders the Full Moon unusually large and luminous. For a Full Moon to earn the Super Moon tag, it should be within approximately 90 percent of its closest distance to Earth.

Blue Moon: A Blue Moon is the second Full Moon in a month that experiences two Full Moons. This phenomenon graces our skies roughly every 2.7 years. Though the term suggests a color, Blue Moons aren’t truly blue. Very occasionally, atmospheric conditions such as recent volcanic eruptions might lend the Moon a slightly blueish tint, but this hue isn’t tied to the term.

Harvest Moon: Occurring closest to the autumnal equinox, typically in September, the Harvest Moon is often renowned for a distinct orange tint it might display. This Full Moon rises close to sunset and sets near sunrise, providing extended hours of bright moonlight. Historically, this was invaluable to farmers gathering their produce.

Common questions about Full Moons

Moonrise over the Syr Darya river in Baikonur, Kazakhstan on Nov. 13, 2016. Credit: NASA/Bill Ingalls

What is the difference between a Full Moon and a New Moon? A Full Moon is witnessed when Earth lies between the Sun and the Moon, making the entire Moon’s face visible. Conversely, during a New Moon, the Moon lies between Earth and the Sun, shrouding its Earth-facing side in darkness.

How does the Full Moon influence tides? The Moon’s gravitational tug causes Earth’s waters to bulge, birthing tides. During both Full and New Moons, the Sun, Earth, and Moon are in alignment, generating “spring tides.” These tides can swing exceptionally high or low due to the combined gravitational influences of the Sun and Moon.

Do Full Moons have an impact on human behavior? While numerous tales suggest Full Moons stir human behavior, causing increased restlessness or even lunacy, rigorous scientific analyses have largely debunked these tales.

Full Moons, in their myriad forms, stand testament to humanity’s enduring captivation with the cosmos. They evoke not just our celestial connection but also tether us to Earth’s rhythms. Whether you’re an avid stargazer or an occasional night sky admirer, Full Moons invariably call for our attention, inviting both introspection and marvel.

Here are the dates for all the lunar phases in 2024:

New First Quarter Full Last Quarter
Jan. 3
Jan. 11 Jan. 17 Jan. 25 Feb. 2
Feb. 9 Feb. 16 Feb. 24 March 3
March 10 March 17 March 25 April 1
April 8 April 15 April 23 May 1
May 7 May 15 May 23 May 30
June 6 June 14 June 21 June 28
July 5 July 13 July 21 July 27
Aug. 4 Aug. 12 Aug. 19 Aug 26
Sept. 2 Sept. 11 Sept. 17 Sept. 24
Oct. 2 Oct. 10 Oct. 17 Oct. 24
Nov. 1 Nov. 9 Nov. 15 Nov. 22
Dec. 1 Dec. 8 Dec. 15 Dec. 22
Dec. 30

New exoplanet discovered in habitable zone of a multi-star system 

A team of professional and citizen scientists has found a Neptune-like exoplanet orbiting one of two Sun-like stars in a binary system. The planet, dubbed TOI 4633 c (and nicknamed Percival), was identified using data from NASA’s Transiting Exoplanet Survey Satellite (TESS). 

The exoplanet was spotted when it passed in front of its host star, TOI 4633 A, temporarily dimming its light like a solar eclipse. The find, published in The Astrophysical Journal, might help astrophysicists understand how planets form around and orbit multi-star systems, opening the door to even more places we can search for exoplanets. 

“Finding planets in multi-star systems is crucial for our understanding of how you can make different planets out of the same material,” said study first author Nora Eisner, a researcher at the Flatiron Institute’s Center for Computational Astrophysics, in a press release. 

Citizen science

Anyone with internet access can easily take part in the online Planet Hunters TESS program, which is part of the larger Zooniverse platform. Oftentimes in science, people are better at spotting certain patterns than computers. In the case of exoplanets, this is true when it comes to exoplanets with long orbits — human volunteers are more likely to flag these than an algorithm which find such signals harder to identify. 

About 43,000 citizen scientists worldwide have aided researchers in cataloging 25 million different objects as part of the project, including TOI 4633 c. Fifteen volunteers noticed the new exoplanet in the data they were examining. So, Eisner and her team decided to take a closer look at it. They identified small wobbles in the host star —  a sign that another object is orbiting close to the star. To confirm if this was the case, the team looked at archival data covering nearly 120 years to discover that the object causing the wobbles was another star, now named TOI 4633 B. It orbits TOI 4633 A every 230 years.

The TOI 4633 star system contains two Sun-like stars, a Neptune-like exoplanet, and a second, unconfirmed Jupiter-like world. Credit: Lucy Reading-Ikkanda/Simons Foundations

The newly discovered exoplanet takes about 272 days to complete one revolution around TOI 4633 A. It is located in the star’s habitable zone, the region around a star where temperatures allow a planet to host liquid water on its surface. This makes TOI 4633 A the brightest star yet known to hold a planet in its habitable zone. However, you could not walk on the exoplanet because it has no solid surface. But if, say, TOI 4633 c had a rocky moon, that world could potentially support life on its solid surface, the researchers said.

New planetary systems

A study from 2017 published in Nature Communications found that Earth-like planets in binary systems could be habitable if they orbited at the right distance. The research was based on models of the Kepler-35 system, where two stars host a Saturn-like planet.

Stars form when cold interstellar gas and dust gathers and collapses; planets are formed from the leftovers in this process. In many cases, there is enough gas and dust to form two or more stars at once, which means astronomers expect that exoplanets with two suns are not uncommon.

“If we were able to constrain where the planets orbit, it would really offer a stepping stone to open up our understanding of exoplanet formation,” Eisner said. “It could also possibly help us someday be able to look at a star and its properties and make some guesses about what planets are potentially orbiting in that system.”

‘It ain’t no garbage.’ Canadian farmer finds chunks of space debris in a remote part of Saskatchewan

Barry Sawchuk and his son were tending to their farmland in southeastern Saskatchewan when they came across several pieces of space junk that may have come from a SpaceX mission, according to reports in the Saskatoon Star Phoenix and AM980 CJME.

“Not every day you go out in your field and find space junk,” the 66-year-old Sawchuk told the Phoenix. “We were just field scouting,” said Sawchuck to CJME’s Gillian Massie. “My son and I were driving around before seeding on April 28, and we came across something that looked like a piece of garbage . . . We pulled over to pick it up, and it ain’t no garbage.” The farmer said the largest piece weighs just shy of 100 pounds (45 kilograms).

Photos made their way to Samantha Lawler, an astrophysicist at the University of Regina, who identified the debris as space junk. Jonathan McDowell, an astrophysicist at Harvard University who specializes in following space launches, said the piece was likely from a SpaceX Dragon craft that returned from the Axiom 3 mission to the International Space Station in February. McDowell projected that its re-entry trajectory passed within a few miles from where Sawchuck found the debris.

The SpaceX Dragon capsule is designed to eject its support module, or trunk, into Earth’s atmosphere, where it should burn up. However, this is not the first case where this did not fully happen. In 2022, space debris from another SpaceX mission was located on Australian farmland. Before this discovery, more SpaceX space debris was found on a farm in Washington state in 2021.

Falling from the sky

It’s likely that more space junk will fall to Earth as more private space companies launch more missions and satellites to space.

According to NOAA’s Department of National Environmental Satellite Data, and Information Service, between 200 to 400 tracked space objects fall to Earth each year. There are about 170 million pieces of space debris currently orbiting Earth. Out of that number, only about 1,000 pieces are actual spacecraft.

The Sky This Week from May 17 to 24: The Moon visits Antares

Friday, May 17
The Moon reaches apogee, the farthest point from Earth in its orbit, at 2:59 P.M. EDT. Luna will then sit some 251,432 miles (404,641 km) away.

By evening, the Moon is close to 4th-magnitude Zavijava (Beta [β] Virginis) in Virgo. How close? Many observers in the U.S. and Canada will see the Moon occult, or pass in front, of, this star overnight.

Note that the timing and duration of any occultation will depend on your location. Some will see the event late on the 17th, while for others it will take place in the early hours of the 18th. You can find a map of where the event is visible and the times it will occur in many major cities on the International Occultation Timing Association’s (IOTA) webpage. Note that times on this page are given in Universal Time.

While we’re focused on the Maiden, let’s also make a quick stop by a favorite double star: Gamma (γ) Vir, also called Porrima. The components of this beautiful binary system are now roughly 3″ apart, which is half the distance they’ll be at their greatest separation. They were last closest in 2005 and have a total orbital period of 169 years. Now easy to split, the stars have nearly identical magnitudes of 3.65 and 3.56 and, as Astronomy contributor Raymond Shubinski writes, “look like two tiny headlights in space.”

Sunrise: 5:43 A.M.
Sunset: 8:11 P.M.
Moonrise: 2:37 P.M.
Moonset: 2:58 A.M.
Moon Phase: Waxing gibbous (71%)
*Times for sunrise, sunset, moonrise, and moonset are given in local time from 40° N 90° W. The Moon’s illumination is given at 12 P.M. local time from the same location.

Path of Comet Olbers in June 2024
Comet Olbers spends most of the month in Lynx. Use bright Castor and Pollux in Gemini to get you to the right region. Credit: Astronomy: Roen Kelly

Saturday, May 18
Jupiter is in conjunction with the Sun at 3 P.M. EDT, rendering the gas giant invisible for now. It will reappear in our morning sky next month.

Comet 13P/Olbers is currently around 8th magnitude and sinking in the west within the boundaries of Auriga the Charioteer this evening after sunset. An hour after the Sun disappears, the comet is 15° high, about 4.5° due north of Beta (β) Tauri, a star that sits at the border of Taurus and Auriga.

Astrophotographers: Pull out your largest scope and favorite camera, and look about 1.2° northwest of Olbers. That will land you on the open cluster NGC 1893, which shines at magnitude 7.5 and stretches some 11′ across. This young gaggle of stars is embedded within the Tadpole Nebula (IC 410), also called the Tadpoles. IC 410 is so named for the two streamers of gas that look like tails in the northeastern region of the nebula. These tails stand out against the dust there, particularly in astrophotos. Tonight you can catch both a comet and this stunning nebular complex in a single shot!

Sunrise: 5:42 A.M.
Sunset: 8:12 P.M.
Moonrise: 3:37 P.M.
Moonset: 3:18 A.M.
Moon Phase: Waxing gibbous (79%)

Sunday, May 19
Asteroid 2 Pallas was the second world discovered in the main belt between Mars and Jupiter. It is the third-largest asteroid in the main belt. Pallas reaches opposition tonight at 11 A.M. EDT, shining at magnitude 9. You can find it amid the stars of Hercules, near that constellation’s Keystone asterism.

Let’s start with the Keystone, which stands 45° high in the east at 10 P.M. local daylight time tonight. It is made up of four stars: Pi (π), Epsilon (ϵ), Zeta (ζ), and Eta (η) Herculis. Tonight, Pallas lies some 6.3° southwest of magnitude 2.8 Zeta, the southwestern point of the Keystone. The main-belt world also lies just ¼° northwest of a slightly brighter 7th-magnitude field star.

Moving back to the Keystone, let’s use it to find a famous globular cluster: M13, also called the Hercules Globular Cluster or the great globular cluster in Hercules. It’s located about one-third of the way along a line drawn from Eta to Zeta Her, so about 2.5° south of Eta Her.

As its name suggests, M13 is both bright — magnitude 5.8 — and big, spanning 20′ (145 light-years in space at its distance from us). It also holds hundreds of thousands of stars and is a favorite target for many amateur astronomers. Visible to the naked eye when there is no Moon, you’ll likely need your binoculars or telescope to enjoy M13 tonight — either will do, as it looks fantastic even at lower magnification. And if you have a bigger scope, look carefully at the core for a faint, Y-shaped dearth of stars often called the propeller.

Sunrise: 5:41 A.M.
Sunset: 8:13 P.M.
Moonrise: 4:36 P.M.
Moonset: 3:37 A.M.
Moon Phase: Waxing gibbous (86%)

Monday, May 20
Let’s move on up from No. 2 to No. 1: Early risers this morning can catch the ruler of the main belt, dwarf planet 1 Ceres, floating off the handle of Sagittarius’ Teapot asterism in the south. Around 4 A.M. local daylight time, the region is some 25° high. Ceres is magnitude 8.2, a relatively easy catch with binoculars. It’s located just under 6.5° northeast of 3rd-magnitude Tau (τ) Sagittarii, which forms the point where the Teapot’s handle begins to curve inward and down toward the base. The largest main-belt world is also within 1° of a close pair of stars that are slightly brighter than Ceres at 5th to 6th magnitude. They lie to Ceres’ northeast.

Thanks to its location in the direction of the galactic bulge, Sagittarius is rich in deep-sky objects, including numerous globular clusters. One of these is M55, which shines at magnitude 6.3 and this morning lies just under 6° south-southeast of Ceres. A relatively “loose” globular, M55 spans some 19′ across — equivalent to 100 light-years in space. It contains roughly 100,000 members, which are some 12.5 billion years old. Try gradually stepping up the magnification on this one, from lower-powered eyepieces to higher ones, and watch how individual stars pop out in increasing numbers as you go.

Sunrise: 5:40 A.M.
Sunset: 8:13 P.M.
Moonrise: 5:38 P.M.
Moonset: 3:57 A.M.
Moon Phase: Waxing gibbous (92%)

Tuesday, May 21
The ringed planet Saturn is climbing in the east in the few hours before dawn, floating among the stars of Aquarius the Water-bearer. Saturn looms large in a telescope, stretching some 17″ across. Its rings are nearly edge-on, with just a bit of their northern side visible. That angle will continue to shrink a little by next month, then slightly grow again later this year before slimming once more as we approach the next ring-plane crossing in 2025.

If you’re able to catch the ringed world around 4:30 A.M. EDT (depending on your location and whether the planet has risen), you’ll notice that its largest moon, Titan, lies just northwest of the disk. Follow Saturn as the sky lightens (or as it rises, for time zones farther west) to see the moon closing in on the disk. Titan disappears behind Saturn in an occultation just after 5 A.M. CDT — note the disappearance is not visible in the Eastern time zone, where the Sun has already risen. The moon won’t reappear from behind the planet’s northeastern limb until just before 7 A.M. PDT, long after sunrise on the West Coast as well.

By tomorrow morning, Titan will have moved far beyond the planet, sitting roughly 1′ to its east. The moon will continue east until the 25th, when it will sit some 3′ from Saturn; after that, its orbit will begin carrying it back toward the ringed world.

Sunrise: 5:40 A.M.
Sunset: 8:14 P.M.
Moonrise: 6:42 P.M.
Moonset: 4:19 A.M.
Moon Phase: Waxing gibbous (96%)

Wednesday, May 22
Because we have a 2D view of the 3D sky, not all objects are as they seem. Take the double star 15 and 17 Canum Venaticorum, high overhead in the southwest a few hours after sunset tonight.

You’ll find this 6th-magnitude pair of stars some 2.8° due east of similarly bright 6th-magnitude Alpha (α) CVn. The two are just under 5′ apart and pretty close in magnitude (6.3 and 5.9 for 15 and 17, respectively). You may notice they look much like a wider version of Porrima in Virgo, which we observed earlier this week.

But you may be waiting for the catch, and here it is: These two stars are not in a binary system. In fact, they’re not close to each other at all! While 17 CVn is relatively close to Earth, at a distance of about 200 light-years, 15 CVn lies far beyond it, some 1,100 light-years away! The “pair” we see is merely a projection on the sky, as is the case with many stellar pairs visible in our skies.

Sunrise: 5:39 A.M.
Sunset: 8:15 P.M.
Moonrise: 7:49 P.M.
Moonset: 4:45 A.M.
Moon Phase: Waxing gibbous (99%)

Full Moon rising with flowers in the foreground
A Full Moon rises over fields of flowers in Lemhi Pass, Idaho, on May 29 2018. Credit: BLMIdaho (Flickr, CC BY 2.0 DEED)

Thursday, May 23
Full Moon occurs this morning 9:53 A.M. EDT. May’s Full Moon is also called the Flower Moon, and you’ll want to catch it later this evening when our satellite passes just 0.4° north of the brilliant red giant Antares at 11 P.M. EDT. The event is readily visible in the eastern half of the U.S., though those farther west may have to wait an hour or two for the pair to rise high enough in the sky for viewing.

If the Moon is above your horizon by 11 P.M. EDT, look southwest to spot it just below Antares, Scorpius’ 1st-magnitude alpha star. Plus, there’s a bonus — a second occultation for portions of the U.S. this week. Observers in the southeastern region of the country will now see the Moon occult Antares, passing in front of the star between about 9 P.M. and 10 P.M. EDT — again, check IOTA’s webpage for the event to see if your location falls within the viewing area and find out when you will see the star disappear and reappear.

Antares is a red giant in the later stages of its life — although it has swelled in size, its temperature has dropped, which is what gives the star its reddish hue. It’s so bright and so red that it is often mistaken for our own Red Planet, Mars. If you want to compare the two, you’ll need to wait several hours, until about 4:15 A.M. local daylight time tomorrow morning — that’s when Mars will rise more than 5° above the eastern horizon and you can see whether you think its brightness and hue match that of Antares, now in the southwest and well clear of the Moon!

Sunrise: 5:38 A.M.
Sunset: 8:16 P.M.
Moonrise: 8:57 P.M.
Moonset: 5:18 A.M.
Moon Phase: Full

Friday, May 24
Last night we viewed Antares, a red giant star in Scorpius. Tonight, let’s look at another particularly red star: Mu (μ) Cephei, also known as Herschel’s Garnet Star or simply the Garnet Star.

This 4th-magnitude sun is some 20° above the northern horizon shortly after 10 P.M. local daylight time tonight. Located in Cepheus the King, it lies south (to the lower right) of the more familiar house-shaped constellation outline, just below the halfway point on a line drawn between Zeta and Alpha Cep. You’ll immediately notice its ruby-red color. That color is a combination of the star’s cool temperature and what astronomers call reddening, as its light travels to us through interstellar dust within the Milky Way. Dust tends to preferentially scatter bluer light away, so we receive only the redder wavelengths of this star’s light, which already trends toward the red end of the spectrum due to its aging nature.

The Garnet star is one of the largest and most luminous stars in the sky. It sits more than 2,000 light-years from Earth. It is also a variable star with a period of some 800 to 1,000 days. Over this timeframe, its brightness can dip and rise again by about a magnitude — certainly noticeable to most observers!

Because it is such a massive star, Mu Cep will someday explode as a brilliant supernova.

Sunrise: 5:37 A.M.
Sunset: 8:17 P.M.
Moonrise: 10:03 P.M.
Moonset: 5:58 A.M.
Moon Phase: Waning gibbous (98%)

Sky This Week is brought to you in part by Celestron.

JWST discovers black holes merging near the dawn of the cosmos

The James Webb Space Telescope (JWST) has detected two galaxies and their supermassive central black holes caught in a merging dance when the universe was only 740 million years old. This makes the find the farthest — and earliest — detection of merging black holes.

The study builds off one the most important results so far from JWST — that galaxies acquire actively feeding black holes at their cores much earlier in the universe’s history than expected. The fact that JWST has now spotted a pair of black holes in the process of merging around the same point in cosmic history suggests that such events could be key to how black holes eventually reach such colossal sizes.

“Our findings suggest that merging is an important route through which black holes can rapidly grow, even at cosmic dawn,” said Hannah Übler, study lead author and astrophysicist at the University of Cambridge, U.K., in a press release. “Together with other Webb findings of active, massive black holes in the distant universe, our results also show that massive black holes have been shaping the evolution of galaxies from the very beginning.”

The findings were published today in Monthly Notices of the Royal Astronomical Society.

Massive voids 

Evidence of black holes merging are seen in three frames from the James Webb Space Telescope.
The merging pair of black holes known as ZS7 is shown in this series of images zooming in on the system. In the rightmost image, JWST was able to clearly see emission from each of the black holes; one black hole is at the bright core of the central object, and the other black hole’s presence is indicated by the red smudge above and just to the right of it. Additional bright objects in the frame — like the one just to the upper right of the merging galaxies — are thought to be companion galaxies, which may be part of the same system of galaxies. Credit: ESA/Webb, NASA, CSA, J. Dunlop, D. Magee, P. G. Pérez-González, H. Übler, R. Maiolino, et al.

We know that black holes form when large stars die in supernova explosions. These resulting garden-variety black holes are typically only a few times more massive than our Sun. But the supermassive black holes at the cores of galaxies are millions or billions of times the mass of the Sun. How black holes grow from masses comparable to a single star into monsters billions of times more massive is not fully understood — but finding an example of black holes in the process of merging within the universe’s first billion years gives clues.

“How do giant black holes get to be so big? Is it through swallowing gas, or each other?” says astrophysicist and author Paul Sutter. “I’m excited by these results because they give us a window into this mysterious process.”

The new pair of black holes detected by JWST, dubbed ZS7, was found by the light the black holes create as they pull in material, heating it and accelerating it to high speeds. Using JWST’s near-infrared spectrograph, astronomers were able to clearly see this fast-moving gas via its Doppler shift and resolve the pair of black holes. JWST had previously found objects of a similar age considered to be candidates for merging black holes, but this result is the strongest evidence yet for a black hole merger this early in the universe.

One of the black holes has a mass 50 million times the mass of our Sun. The other black hole might also be around the same size, but it is harder to measure because it was surrounded by dense gas, said study co-author Robert Maiolino, also from the University of Cambridge, in the ESA press release.

Future gravitational waves

When the two black holes do merge, they will generate gravitational waves that would be strong enough to be detected by future missions, such as the ESA’s recently approved Laser Interferometer Space Antenna (LISA) mission. Consisting of a trio of spacecraft, LISA would be the first space-based observatory dedicated to studying gravitational waves.

The prospect of it being able to detect systems like ZS7 is enticing to researchers. “Webb’s results are telling us that lighter systems detectable by LISA should be far more frequent than previously assumed,” said LISA Lead Project Scientist Nora Luetzgendorf of the European Space Agency. “It will most likely make us adjust our models for LISA rates in this mass range. This is just the tip of the iceberg.”

Found: An Earth-sized exoplanet named SPECULOOS-3 b

An international team of astronomers has discovered exoplanet SPECULOOS-3 b and its ultra-cool red dwarf star, some 55 light-years away from Earth.

Despite being the size of Earth, the newly discovered exoplanet could not be more different from our home planet. According to the NASA news release from May 15, this terrestrial world is baked by high levels of radiation from its sun, probably leaving the planet without an atmosphere. It orbits its star in 17 hours, as opposed to our year. And the planet is likely tidally locked, meaning one side always faces the sun while the other is shrouded in darkness.

The red dwarf star is also very different from our own Sun: The Jupiter-sized SPECULOOS-3 was discovered to be 4,760 degrees Fahrenheit (2,627 degrees Celsius), several thousand degrees cooler than the Sun, and much dimmer as well.

The discovery of this exoplanet comes from the Belgium-based SPECULOOS (Search for Planets EClipsing ULtra-cOOl Stars) project, an international network of telescopes in search for dim stars in our galaxy and the rocky planets that orbit them. The goal is to identify dozens of planetary systems and even more red dwarfs, in the hope of finding habitable exoplanets and signs of life. The name of the mission is a play on words with the Belgian speculoos cookies (which fans of Trader Joe’s may recognize too).

The data from SPECULOOS-3 b discovery could lead to further research using the James Webb Space Telescope, according to the release. Its planetary composition and its location are subject to more research.

‘‘We’re making great strides in our study of planets orbiting other stars. We have now reached the stage where we can detect and study Earth-sized exoplanets in detail. The next step will be to determine whether any of them are habitable, or even inhabited,’’ said Steve B. Howell, one of the planet’s discoverers at NASA Ames Research Center, in the release.

Secret Sky: Undset’s forgotten mountain

On the evening of Sept. 23, 2023, I was training my 3-inch Tele Vue refractor on the Moon to catch sunrise over Lambert Crater when a brilliant pyramid of light just to the east of the crater grabbed my attention instead. This isolated peak was the brightest feature to emerge from the lunar twilight that night. At high power, the mountain’s sharply cut facets reflected the rising Sun’s rays in the most alluring manner. I immediately had to know the mountain’s name, only to discover … it has none.

But it did once! I’ll explain.

The next morning, I checked NASA’s online Scientific Visualization Studio’s Moon Phase and Libration (which displays the Moon on any chosen date with countless labels), as well as the Lunar Reconnaissance Orbiter Camera ACT-REACT QuickMap, but neither site identified this peak. Nor was the mountain listed in the International Astronomical Union’s (IAU) Gazetteer of Planetary Nomenclature for the Moon.

Doubtful that such a bright feature went unnamed, I went back in time to the 1913 Collated List of Lunar Formations. Sanctioned by the International Association of Academies, this work was the first attempt to remedy the unsatisfactory state of lunar nomenclature of the day. (At that time, the Moon’s most prominent features were known by at least three different names, depending on the source.) I was not disappointed: The Collated List provides us with the first official mention of our target mountain’s name: Lambert Gamma (Γ).

This section of image 40B4 from the 1973 Lunar Topographic Orthophotomap Series displays Mons Undset misspelled as “Mons Undest.” Credit: NASA

German astronomer Johann Henrich Mädler assigned that name to the mountain in his and Wilhelm Beer’s Mappa Selenographica (1836), which was then the universally accepted standard in selenography. Mädler’s convention was to name isolated lunar peaks wtih the name of a nearby crater followed by a Greek letter. In his 1876 book The Moon and the Condition and Configurations of Its Surface, Edmund Neison gives a wonderful description of Lambert Γ: “Owing to its curved form, the mountain Γ … appears at times like a crater … Occasionally this peak glitters on the terminator in a very striking manner.”

Lambert Γ’s uppercase Gamma was changed to the lowercase Lambert γ in the 1935 Named Lunar Formations, the first official list of IAU nomenclature. When the IAU discontinued the use of Greek letters for elevated features in 1973, Lambert γ was renamed Mons Undset, in honor of Sigrid Undset, a Danish-born Norwegian novelist who won the 1928 Nobel Prize in literature.

Unfortunately, when Undset’s name was applied to her lunar mountain in the 1973 Lunar Topographic Orthophotomap Series — the first comprehensive and continuous mapping based on photographs from Apollo 15, 16, and 17 — her name was misspelled “Undest.” Rather than fixing the mistake, the IAU stripped the mountain of its name, leaving it in nomenclature limbo.

Most references today lean toward unofficially renaming the mountain Lambert γ, but why take away an honor bestowed upon a great woman just because of a typo? (For what it’s worth, in 1985 the IAU named a crater on Venus in Undset’s honor ­— but we cannot visually admire this sight.)

My observation of Mons Undset occurred at lunar colongitude 18.3˚, which must have been one of the occasions Neison mentioned, when the mountain appears as a striking site near the terminator. But Mons Undset is so unusual at times that observers have mistaken it for a lunar transient phenomenon. So, it’s a sight worth pursuing — and remembering.

In her book Christmas and Twelfth Night, Undset writes, “Let us remember that He has given us the sun and the moon and the stars.” And lest we forget, we gave her a mountain on the Moon. As always, send your thoughts to sjomeara31@gmail.com.

Your best pictures of this past weekend’s aurorae

The geomagnetic storm that struck Earth on May 10 was the strongest in 21 years — exceeding forecasts and bringing the spectacle of the aurora borealis south (and the aurora australis north) to millions of people who had the chance to see it for the first time.

A lot has changed since 2003, the last time Earth experienced a solar storm as strong as this one. One profound difference is that most of us now walk around with cameras in our pockets good enough to take pictures of aurorae. For the first time in human history, we were all able to see, capture, and share our views of this natural wonder in real time.

Astronomy readers sent us photos from all around the world — and here are some of our favorites.

Rob Lyons, taken from Vancouver, Canada. This image is a still from a timelapse video shot with a Sony A7R mirrorless camera and a Sigma 14mm f/1.4 lens.
Gianni Tumino, taken from Chiaramonte Gulfi, Sicily, Italy. Canon EOS R5 mirrorless camera and 15–35mm zoom lens at f/3.5, taking 129 ten-second exposures at ISO 6400.
Katelyn Beecroft, taken from just outside of London, Ontario, Canada. Canon Rebel T6i DSLR, Rokinon 14mm lens at f/2.8, ISO 800, 10-second exposure.
Chirag Upreti, taken from Ashokan Reservoir in New York. Sony a7R III mirrorless camera, Sigma 14–24mm lens at 14mm and f/2.8; single 10-second exposure at ISO 800.
Chirag Upreti, taken from Ashokan Reservoir in New York. Sony a7 III mirrorless camera (astromodified) and 12–24mm lens at 12mm and f/4, ISO 1000, 15-second exposure.
John Chumack, taken from Yellow Springs, Ohio. Canon EOS 6D DSLR, 16mm lens at f/2.8, ISO 800, 10-second exposure.
Stephen Dorn, taken from southwest New Mexico. Sony a7R III, Sigma Art 24mm lens at f/1.4, ISO 1600, 10-second exposure. In addition to the aurora filling the frame, this image also captures meteor streaks on the right side of the image.
  • This storm was powerful enough to give many viewers the experience of a coronal aurorae. Standing directly underneath an aurora causes it to appear to radiate from a single point as charged particles from space rain down on Earth’s atmosphere. Credit: Tania Wood from Collingwood, Ontario, Canada
Philippe Moussette, taken from Petit lac à l’Épaule, Quebec, Canada. Canon EOS R3 mirrorless camera and 8–15mm fisheye lens.
Chris Cook, taken from Mount Wilson overlooking Los Angeles (34° north latitude). Canon EOS 6D Mk II DSLR, Tamron 15–30mm f/2.8 lens, ISO 1600, 15-second exposure.
Chris Cook, taken from Mount Wilson overlooking Los Angeles (34° north latitude). Canon EOS 6D Mk II DSLR, Tamron 15–30mm f/2.8 lens, ISO 1600, 15-second exposure.
Abhijit Patil, taken from Death Valley National Park, California. Nikon Z 6II mirrorless camera (astromodified) and 14–24mm lens at 14mm and f/2.8, ISO 2000, 10-second exposure.
Abhijit Patil, taken from Death Valley National Park, California. Nikon Z 6II mirrorless camera (astromodified) and 14–24mm lens at 14mm and f/2.8, 10-second sky exposure at ISO 2000 and 30-second foreground exposure at ISO 3200.
Hossein Nasri, taken from the Seh Qaleh Desert in South Khorasan, Iran (33° north latitude). Canon EOS 6D DLSR and 24–70mm lens at 24mm and f/3.2, ISO 3200, panorama of six 30-second exposures.
René Saade, taken from Chirimoyos (23.4° north latitude), near Mazatlán, Mexico, on May 11, 2 A.M. local time. Sony a7S II mirrorless camera and Sigma Art 35mm lens at f/1.4, ISO 3200, panorama of three stacks of five 8-second exposures.

NASA’s asteroid Bennu samples have rocks unlike any meteorite ever found

In 1877, when English geologist Henry Clifton Sorby first examined samples of meteorites under a microscope, he saw small, spherical rocks and described them as “drops of fiery rain.” Now known as chondrules, from the ancient Greek chondros, meaning “grain”, they are present in nearly all meteorites and, hence, are thought to be a major part of the building blocks of planets. Yet, the processes that formed them remain enigmatic today.

Today, planetary scientists can study not only rocks that have fallen from the sky — they have begun to look for chondrules in materials directly sampled from asteroids to learn more. Most recently, researchers have started analyzing materials returned from asteroid 101955 Bennu, and presented their initial findings at the Lunar and Planetary Science Conference in The Woodlands, Texas, earlier this year.  

So far, researchers have not found anything in Bennu samples that looks exactly like chondrules seen in meteorites. But they have found an array of rocks that resemble chondrules to varying degrees, suggesting that asteroids are more diverse than meteorites might suggest.

Excavating Bennu’s past

In October 2020, NASA’s OSIRIS-REx spacecraft touched down on Bennu and collected a sample of surface material, stowing it in a capsule that the spacecraft returned to the Utah desert Sept. 24, 2023. The next day, the 4.29-ounce (121.6 grams) sample was safely stored at NASA’s Johnson Space Center in Houston.

Although the groups are in the early stages of analysis and have examined less than 1 percent of the sample returned, the results are “still very important findings,” says Harold Connolly Jr., a meteorite expert at Rowan University.

Curation teams process the sample return capsule from NASA’s OSIRIS-REx mission in a cleanroom in 2023. Credit: NASA.

Connolly Jr. led the initial analysis of one of the Bennu samples. This process is akin to what geologists do when they find rocks on Earth and involves documenting the appearance of particles and identifying minerals and possible processes that altered them. Through this work, researchers hope to infer what the sample was like when it formed.

This first analysis showed that Bennu has no definitive chondrules. That finding is in line with Bennu’s mineral evidence, which shows that water once flowed through the asteroid as the ices it contained melted long ago.

“The aqueous alteration would have destroyed the chondrules it may have had,” says Sara Russell, a meteorite researcher at the Natural History Museum in London who led another analysis of a sample.

However, Russell and her team’s results showed that the sample contains grains that could be fragments of chondrules. The group is currently looking at whether the remnants could be from another type of rock that is thought to have formed in the solar system even earlier than chondrules — known as calcium-aluminum-rich-inclusions or CAIs. If not, the fragments would likely be from chondrules that escaped being altered by the water.

In another abstract presented at the conference, a team led by meteorite experts Loan Le and Kathie Thomas-Keprta at the Johnson Space Center found three grains in a millimeter-sized-sample of Bennu that have similar compositions and shapes to a chondrule found in a meteorite that fell over Australia in 1969 called Murchison. Two of the objects in the Bennu sample have indentations, possibly from contact with water that once flowed through asteroid. Thomas-Keprta says the other object’s structure, which resembles bales of hay, has never been observed before in a chondrule, as far as she is aware.

In the coming months, the team plans to slice a 100-nanometer-thin sample of the grains to see if they contain other materials that are commonly found in chondrules.

For now, they are calling the grains chondrule-like-objects.

This view of asteroid Bennu ejecting particles from its surface on Jan. 6, 2019
This view of asteroid Bennu ejecting particles from its surface on Jan. 6, 2019, was created by combining two images taken by the NavCam 1 imager aboard NASA’s OSIRIS-REx spacecraft. Credit: NASA.

The diversity of asteroids

If the materials are found to be chondrules, they will show that the population of asteroids in our solar system span a wider variety than indicated by meteorites found on Earth’s surface. And Bennu’s chondrule-like objects suggest that it may be a bit different from any known meteorite, says Russell.

Interestingly, researchers also found chondrule-like objects in the sample brought back from asteroid 162173 Ryugu by Japan’s Hayabusa2 mission in 2020.

“What we are learning from Ryugu and Bennu is that there are lots of asteroids out there that are similar, but don’t exactly match the meteorites in our collections,” says Russell.

As for whether the returned samples have been able to answer the long-standing question of how chondrules formed, Connolly Jr. says, “Not yet.” He adds that discovering how they formed isn’t easy, though further analysis of the Bennu sample and more spacecraft missions to return more materials could help.

“You have to find the right pond and the right fish,” he says.

If scientists can discover how chondrules formed, they would have a better sense of the extent to which they were building blocks of planets. It’s possible that chondrules formed when small grains of dust were heated early on in the solar system and later cooled. If this is the case, then chondrules would have been a large source of the materials that accreted to build asteroids, comets, and planets.

On the other hand, if chondrules could have only formed from collisions between planetesimals that had already been built, then chondrules would not have been necessary to form planets — though they would still stand as evidence that the early solar system was a dynamic, violent place.

It could turn out that chondrules formed in multiple ways, depending on where in the solar system they formed and when.

“Chondrules are so unusual,” says Thomas-Keprta. “They would never have been predicted if they didn’t exist.”

‘Hairy’ black holes may get a massive glow-up from the LISA spacecrafts

Physicists consider black holes one of the most mysterious objects that exist. Ironically, they’re also considered one of the simplest. For years, physicists like me have been looking to prove that black holes are more complex than they seem. And a newly approved European space mission called LISA will help us with this hunt.

Research from the 1970s suggests that you can comprehensively describe a black hole using only three physical attributes – their mass, charge and spin. All the other properties of these massive dying stars, like their detailed composition, density and temperature profiles, disappear as they transform into a black hole. That is how simple they are.

The idea that black holes have only three attributes is called the “no-hair” theorem, implying that they don’t have any “hairy” details that make them complicated.

Hairy black holes?

For decades, researchers in the astrophysics community have exploited loopholes or work-arounds within the no-hair theorem’s assumptions to come up with potential hairy black hole scenarios. A hairy black hole has a physical property that scientists can measure – in principle – that’s beyond its mass, charge or spin. This property has to be a permanent part of its structure.

About a decade ago, Stefanos Aretakis, a physicist currently at the University of Toronto, showed mathematically that a black hole containing the maximum charge it could hold – called an extremal charged black hole – would develop “hair” at its horizon. A black hole’s horizon is the boundary where anything that crosses it, even light, can’t escape.

Aretakis’ analysis was more of a thought experiment using a highly simplified physical scenario, so it’s not something scientists expect to observe astrophysically. But supercharged black holes might not be the only kind that could have hair.

Since astrophysical objects such as stars and planets are known to spin, scientists expect that black holes would spin as well, based on how they form. Astronomical evidence has shown that black holes do have spin, though researchers don’t know what the typical spin value is for an astrophysical black hole.

Using computer simulations, my team has recently discovered similar types of hair in black holes that are spinning at the maximum rate. This hair has to do with the rate of change, or the gradient, of space-time’s curvature at the horizon. We also discovered that a black hole wouldn’t actually have to be maximally spinning to have hair, which is significant because these maximally spinning black holes probably don’t form in nature.

Detecting and measuring hair

My team wanted to develop a way to potentially measure this hair – a new fixed property that might characterize a black hole beyond its mass, spin and charge. We started looking into how such a new property might leave a signature on a gravitational wave emitted from a fast-spinning black hole.

A gravitational wave is a tiny disturbance in space-time typically caused by violent astrophysical events in the universe. The collisions of compact astrophysical objects such as black holes and neutron stars emit strong gravitational waves. An international network of gravitational observatories, including the Laser Interferometer Gravitational-wave Observatory in the United States, routinely detects these waves.

Our recent studies suggest that one can measure these hairy attributes from gravitational wave data for fast-spinning black holes. Looking at the gravitational wave data offers an opportunity for a signature of sorts that could indicate whether the black hole has this type of hair.

Our ongoing studies and recent progress made by Som Bishoyi, a student on the team, are based on a blend of theoretical and computational models of fast-spinning black holes. Our findings have not been tested in the field yet or observed in real black holes out in space. But we hope that will soon change.

LISA gets a go-ahead

In January 2024, the European Space Agency formally adopted the space-based Laser Interferometer Space Antenna, or LISA, mission. LISA will look for gravitational waves, and the data from the mission could help my team with our hairy black hole questions.

Formal adoption means that the project has the go-ahead to move to the construction phase, with a planned 2035 launch. LISA consists of three spacecrafts configured in a perfect equilateral triangle that will trail behind the Earth around the Sun. The spacecrafts will each be 1.6 million miles (2.5 million kilometers) apart, and they will exchange laser beams to measure the distance between each other down to about a billionth of an inch.

LISA will detect gravitational waves from supermassive black holes that are millions or even billions of times more massive than our Sun. It will build a map of the space-time around rotating black holes, which will help physicists understand how gravity works in the close vicinity of black holes to an unprecedented level of accuracy. Physicists hope that LISA will also be able to measure any hairy attributes that black holes might have.

With LIGO making new observations every day and LISA to offer a glimpse into the space-time around black holes, now is one of the most exciting times to be a black hole physicist.

This article was first published on The Conversation. It is republished here under a Creative Commons license.

How old is each planet in our solar system?

How old is each planet? Do we know the order in which the planets in our solar system formed?

Robert Hawk
Canal Winchester, Ohio

Estimating ages of specific events is one of the most difficult problems in astrophysics. While we have a precise (and probably accurate) age for the solar system, we do not have precise ages for each planet.

The solar system’s age comes from radiometric dating of rock samples from Earth, the Moon, and meteorites. If an isotope of one element decays into an isotope of another element, then measuring the ratio of both to a stable isotope of either element lets you work backwards to determine how many half-lives have passed since the initial concentration. (One half-life is the time it takes for half of a radioactive parent isotope [or radionuclide] to decay into its product, or daughter, isotope, with half of the parent remaining.) This only works for situations where elemental concentrations do not get mixed up between different material samples (e.g., the system is “closed” — adding in fresh material with different initial values of the radiogenic material, or indeed bulk elemental composition differences, will invalidate the analysis), one has radioactive elements of the right half-life, and these elements are in large enough concentrations to measure. Using this technique, we find that the absolute age of Earth is 4.54 billion years old, with an uncertainty of only 1 percent.

We can also determine relative ages of various rocks using extinct radionuclides, such as aluminum-26 (which decays into magnesium-26), whose half-life is so short (0.72 million years) that its original concentrations are now unmeasurable. The clock is usually set by the initial concentrations found in calcium-aluminum-rich inclusions, or CAIs — the first solids in the solar system — in meteorites, and we can measure ages relative to those. This technique gives relative ages good to half a million years for rocks from the first 10 million years of the early solar system (such as meteorite fragments or interplanetary dust grains). Other isotopic systems with different half-lives can be used to date specific events, like the formation of Earth’s core, which is related to the giant impact that formed the Moon.

Our best guess is that the gas giant planets — Jupiter and Saturn — formed first from the gas-rich disk that accompanied the formation of the proto-Sun. Of the planets, Jupiter and Saturn’s compositions are most like the Sun. However, even they have higher concentrations of heavy elements (beyond hydrogen and helium on the periodic table) compared to our Sun. This is evidence that even early on, solid materials that formed from these heavy elements — like silicon-oxygen-rich and carbon-rich dust, as well as ices that form at various distances from the Sun — play an important role in planet formation.

We suspect that the ice giants Uranus and Neptune formed next because they have gas-to-dust ratios intermediate between the big gas giants and the rocky terrestrial planets (Mercury, Venus, Earth, and Mars). Uranus and Neptune likely formed just as the gas disk that accompanied the forming Sun was dissipating, on a timescale of less than 10 million years. Next to form were the rocky inner planets. While their initial building blocks probably came together quickly to form planetary embryos, it took between 10 million to 100 million years after the gas disk was gone for these building blocks to further crash into each other and form the terrestrial planets we know today. We can estimate the time since a terrestrial planet’s surface was last “reset” (e.g., globally altered, such as by lava flows) based on crater counting, but those times are not formation ages. And finally, the dwarf planets in the outer solar system are still growing slowly.

Nailing down this sequence of events is of consequence for exoplanetary systems as well, which we can study with both theoretical models and observations. A Jupiter-like gas giant that forms early beyond the ice line (where it is cold enough for volatiles like water, ammonia, and carbon dioxide to exist as ices) probably has a strong impact on the delivery of water and other materials to potentially habitable planets. The evolution and final architecture of planetary systems have a lot to tell us about how planets form, as well as the prospects for life in the universe.

And, of course, we still have a great deal to learn when it comes to our own solar system as well.

Michael Meyer
Professor of Astronomy, University of Michigan Ann Arbor, Michigan

How and when to see the ISS, without a telescope

Lots of things change in the night sky. Stars rise and set during the night; constellations come and go as the seasons pass; planets waltz along the ecliptic, visiting the zodiacal constellations on their nonstop sightseeing tour of the heavens; and shooting stars zip across the sky. Sometimes, a display of the fabled aurora paints the northern sky with searchlight beams of scarlet and swaying curtains of highlighter-pen green.

But all these things only happen occasionally. You can’t be guaranteed to see each of them every night.

However, there is one thing you can be guaranteed to see moving in the sky every night, no matter where you live on the planet: satellites.

A sky full of satellites

Years after the launch of Sputnik in 1957, there are thousands of satellites orbiting Earth. And it’s no exaggeration to say that they have become an essential part of our infrastructure. Every minute of every day, satellites are taking photos of the weather, transmitting TV and radio signals, monitoring the climate, and linking people around the world. They steer our cars, guide our planes and ships, and, perhaps most important, allow us to watch cute cat videos while lazing on a beach.

In recent years, the number of satellites orbiting Earth has — if you’ll pardon the pun — skyrocketed, particularly as SpaceX has pursued its mission to fill low Earth orbit with its Starlink Wi-Fi satellites, launching some 50 at a time atop its reusable Falcon rockets. While there’s no doubt these are useful to people in remote locations, allowing them to connect to the internet for the first time in some cases, both amateur and professional astronomers are deeply concerned about their impact on the night sky and astronomical research.

But there is one satellite that, perhaps hypocritically, watchers of the night sky enjoy. Some even go out of their way to see it: the International Space Station (ISS).

How to see the ISS

So, how do you see the ISS for the first time, tonight?

  • First, check NASA’s web site (there are also apps) to see if it’s visible — you may have to wait a few days until it is. If the ISS will put in an appearance tonight, use your most reliable weather app to check the forecast — again, you might have to wait a few days!
  • Next, choose your observing site carefully. The more you can see of the sky, the better. During high passes, the ISS clears most trees and buildings, but a low pass might be hidden by features on your horizon, so figure out in advance where you should go to ensure you see it.
  • Be at your observing site a good 10 or even 15 minutes before the ISS pass is due to begin. Then, look for a “star” rising in the west at the predicted time. If you see one that’s flashing, it’s a plane. If it’s shining with a steady light, it’s the ISS. It won’t look particularly bright at first, but it will grow brighter as it gains height. Then, just follow the ISS across the sky, enjoying the sight of it cruising through the constellations, passing background stars and planets along the way.
  • If you have a pair of binoculars handy, definitely swing them toward the ISS. They will enhance its color and brightness a lot. But even if you don’t have any, just enjoy watching it with your naked eye. It’s still a thrilling sight.
  • Eventually the ISS will fade as it moves out of direct sunlight and into Earth’s shadow, effectively going into eclipse. Sometimes it fades slowly, as if on a dimmer switch, while other times it almost appears to be snuffed out like a candle. But eventually it will be gone, surrendering the night sky to the stars once more.
  • And that’s how you see the ISS. As the saying goes, it’s not rocket science. It’s just a matter of looking at the right time from the right place.
  • One last thing. As you’re watching the ISS go over, give it a wave. You never know, the crew might be looking down at you just as you’re looking up at them!

The ISS essentially looks like a starlike point of light that moves across the sky from west to east. However, it is not visible from every location every night. Sometimes it can be seen in the wee small hours before sunrise, sometimes as the evening sky is darkening after sunset. Unlike an airplane, the ISS doesn’t blink or flash, instead shining with a steady light.

How impressive the ISS looks during any particular pass depends on where it is in its orbit and where you are when you’re looking up at it. Sometimes its track carries it very high in the sky, even overhead, while other times it’s a lot lower, scraping the trees. The higher its altitude, the brighter the ISS will appear. At its brightest, the ISS can nearly rival Venus at its best, and is a genuinely stunning sight as it arcs across the sky, looking like a lantern that someone has thrown up into it.

I took a picture of the International Space Station this morning, from my back yard.
byu/120decibel inspace

Editor’s note: This article was first published in 2023 and has been updated.