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The Sky This Week from March 15 to 24

The Big Dipper returns to prominence in the March evening sky, while three bright planets continue to rule the predawn hours.

BigDipper
The Big Dipper

The Big Dipper sets behind a windmill located in Show Low, Arizona. This week, observers can catch the bright asterism climbing higher in the evening sky. The Dipper is the most conspicuous part of the constellation Ursa Major the Great Bear.

John Vermette
Friday, March 15
The Big Dipper’s familiar shape rides high in the northeast on March evenings. The spring sky’s finest binocular double star marks the bend of the Dipper’s handle. Mizar shines at 2nd magnitude, some six times brighter than its 4th-magnitude companion, Alcor. Even though these two are not physically related, they make a fine sight through binoculars. (People with good eyesight often can split the pair without optical aid.) A small telescope reveals Mizar itself as double — and these components do orbit each other.

Saturday, March 16
Although asteroid 3 Juno reached opposition and peak visibility back in November, it remains a worthwhile target this week. Not only is it still reasonably bright — a small telescope will reveal its 9th-magnitude glow — but it also resides against the rich stellar backdrop of Orion the Hunter. This evening provides your best opportunity because the asteroid passes just 0.1° north of 5th-magnitude Pi11) Orionis. This star marks the northernmost point in Orion’s Shield.

Sunday, March 17
Venus continues to dominate the predawn sky from its perch in northern Capricornus. The inner world shines at magnitude –4.0, nearly two magnitudes brighter than the second-brightest planet, Jupiter. Venus rises around 5:30 a.m. local daylight time and stands some 10° high in the east-southeast 45 minutes before the Sun comes up. When viewed through a telescope, Venus shows a disk that spans 14" and appears about three-quarters lit.

Jupitermoons
A jovian triple play

Track Europa and Ganymede as they pass in front of Jupiter's cloud tops at the same time Io emerges from behind the giant planet's disk.

Astronomy: Rick Johnson
Monday, March 18
Jupiter continues to grow more prominent before dawn. The giant planet shines at magnitude –2.1 and climbs 30° high in the south-southeast by the first hint of twilight. A telescope reveals at least two conspicuous cloud belts on Jupiter’s 38"-diameter disk. And this morning, Jupiter’s brightest moons provide an extra treat as both Europa and Ganymede transit the gas giant’s disk while Io re-emerges from behind the planet. Europa starts the action when it touches Jupiter’s northeastern limb at 4:01 a.m. EDT, with Ganymede following at 5:04 a.m. Both satellites transit the planet’s northern hemisphere, with Europa closer to the equator. Ganymede is not even halfway across when Io reappears from behind Jupiter’s southeastern limb at 5:51 a.m.

Tuesday, March 19
Although Saturn passed on the opposite side of the Sun from Earth in January, it already appears conspicuous in the southeast before dawn. From mid-northern latitudes, the ringed planet lies 20° above the horizon as twilight begins. Saturn shines at magnitude 0.6 and appears significantly brighter than any of the background stars in its host constellation, Sagittarius the Archer. A telescope shows the gas giant’s 16"-diameter disk and a spectacular ring system that spans 36" and tilts 24° to our line of sight.

The Moon reaches perigee, the closest point in its orbit around Earth, at 3:48 p.m. EDT. It then lies 223,307 miles (359,377 kilometers) away from us.

Wednesday, March 20
Full Moon occurs at 9:43 p.m. EDT, but our satellite will look completely illuminated all night. You can find it rising in the east around sunset and peaking in the south at about 1:30 a.m. local daylight time. The Moon spends the night among the background stars of western Virgo.

For those of you tired of winter weather, good news: Spring officially begins today. Earth’s vernal equinox occurs at 5:58 p.m. EDT, which marks the moment when the Sun crosses the celestial equator traveling north. The Sun rises due east and sets due west today. If the Sun were a point of light and Earth had no atmosphere, everyone would get 12 hours of sunlight and 12 hours of darkness. But our blanket of air and the finite size of our star make today a few minutes longer than 12 hours.

Thursday, March 21
The variable star Algol in Perseus reaches minimum brightness for a couple of hours centered on 10:04 p.m. EDT, when it shines at magnitude 3.4. If you continue viewing over the next few hours, you can watch it more than triple in brightness, to magnitude 2.1. This eclipsing binary star runs through a cycle from minimum to maximum and back every 2.87 days. Algol lies about halfway to the zenith in the west-northwest after sunset and sinks low in the northwest after midnight.

ZL
The zodiacal light
The Himalayan Chandra Telescope sits in the foreground at an altitude of 14,800 feet near Hanle, Kashmir, India, while the zodiacal light helps illuminate the background. We also see brilliant Venus at the left (behind the thin cloud), a meteor passing to the right of the observatory, and a geostationary satellite passing at the upper right.
Navaneeth Unnifrishnan
Friday, March 22
March evenings offer an excellent chance to see the zodiacal light. From the Northern Hemisphere, late winter and early spring are great times to observe this elusive glow after sunset. It appears slightly fainter than the Milky Way, so you’ll need a clear moonless sky and an observing site located far from the city. With the waning gibbous Moon now exiting the early evening sky, prime viewing conditions extend from tonight through April 6. Look for the cone-shaped glow, which has a broad base and points nearly straight up from the western horizon, after the last vestiges of twilight have faded away.

Saturday, March 23
Mars continues to put on a nice show these March evenings. It appears more than 30° high in the west once twilight fades to darkness and doesn’t set until after 11 p.m. local daylight time. The magnitude 1.4 Red Planet crosses the border from Aries the Ram into Taurus the Bull today, setting up a dramatic conjunction with the beautiful Pleiades star cluster (M45). Mars remains within the same binocular field as the cluster from tonight until early April, and will pass 3° south of M45 a week from now. Unfortunately, Mars shows little if any detail on its 5"-diameter disk when viewed through a telescope.

Sunday, March 24
One of the sky’s largest asterisms — a recognizable pattern of stars separate from a constellation’s form — occupies center stage after darkness falls on March evenings. To trace the so-called Winter Hexagon, start with southern Orion’s luminary, Rigel. From there, the hexagon makes a clockwise loop. The second stop is brilliant Sirius in Canis Major. Next, pick up Procyon in the faint constellation Canis Minor, then the twins Castor and Pollux in Gemini, followed by Capella in Auriga, Aldebaran in Taurus, and finally back to Rigel.

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