Explore nearby deep sky gems

Note the red dwarf’s change in position between 1950 (right) and 2010 (left).

The most common stars in the Milky Way are not visible to the naked eye. Red dwarfs are inherently dim, and only those located near us are bright enough to be seen through the typical hobbyist telescope. The closest is Proxima Centauri, just 4.2 light-years from Earth. At 11th magnitude, it is 100 times fainter than the naked eye can see. It is also deep in the southern sky, below the horizon for most U.S. observers.

The next closest red dwarf, at 6 light-years away, is Barnard’s Star, discovered by Edward Emerson Barnard in 1916. It has the distinction of being the fastest star (known as “proper motion”) in the sky relative to the Sun. Since Barnard’s Star was discovered, it has moved 17.7'. That’s slightly more than half the Moon’s apparent diameter. That may not sound like much, but compared to the other stars, it’s haulin’ hydrogen!

Observing tip: Use a star chart to pick this 9.5-magnitude star out of a rich star field.

Imagine a hot star the size of Earth, but with the mass of the Sun. The transition begins as a Sun-like star becomes a red giant, like Aldebaran (Alpha [α] Tauri). It then ejects its outer layers to form a planetary nebula, and eventually settles down as a white dwarf. Our Sun is destined to become a white dwarf in about 5 billion years.

In the meantime, the closest white dwarf, Sirius B (Alpha Canis Majoris B), is only 8.6 light-years away. It is the companion of Sirius A, the brightest star in the night sky. Originally, Sirius B was brighter and more massive than Sirius A, but it aged faster and evolved into a white dwarf around the time the Cretaceous raptor Deinonychus prowled North America. Although it is brighter than Barnard’s Star, the glare of its luminous companion makes it a challenge to see. It’s currently about 10" east of the primary, approaching the most distant part of its 50-year orbit. That means it is easier to see now than it will be in 25 years.

Observing tip: Let Sirius drift through your eyepiece’s field of view; the companion lies to the east and will follow. High magnification and a steady sky are your friends. And light pollution won’t have much effect on your view.

Double stars orbit around a gravitational center called the barycenter. Such systems may have similar stars — or different, if one has greater mass and evolves more quickly than the other. 

61 Cygni is an example of a system with two similar stars. It’s not the closest binary to the Sun (Alpha Centauri and Sirius are closer) but is the nearest one north of the celestial equator. This system’s claim to fame is being the first to have its distance measured with a fair degree of accuracy. In 1838, using the stellar parallax method, Friedrich Wilhelm Bessel came up with 10.3 light-years — though today’s research shows it to be 1.1 light-years more distant. This is a pair of K-type dwarf stars that complete an orbit in 659 years. Like Barnard’s Star, it’s a “fast” mover — the fastest visible to the naked eye. With a primary of magnitude 5.2 and a secondary that glows at magnitude 6.0, it’s hard to pick out with the naked eye under an urban sky.

Observing tip: The stars are separated by a generous 28", so it’s easy to resolve them through a small telescope and distinguish their orange hue.

The famous saying about “not seeing the trees for the forest” can also apply to groups of stars called open clusters. Just as a foreground tree can blend into a forest when viewed from afar, a foreground star can blend into a open cluster when they are both viewed along the same line of sight. Such is the case for the Hyades. 

The Hyades, which forms the head of Taurus the Bull, is the nearest open cluster. Because it’s only 153 light-years from us, it has an apparent diameter greater than 5°. Its true diameter exceeds 20 light-years. Even after an estimated 625 million years, the stars are still moving together. Aldebaran, the brightest star in Taurus, is only 65 light-years away. However, its apparent association with the Hyades is simply a coincidence. 

Observing tip: The best views of the Hyades usually come through binoculars or a small rich-field telescope.

In about 5 billion years, the Sun will shed its outer layers of gas to become a planetary nebula, leaving behind a white dwarf in the center. Through the same process, an ancient star expelled varying densities of ionized gas — especially oxygen — to give this next nebula its name. 

The Helix Nebula (NGC 7293) is an older planetary, so the gas has traveled far enough to appear as a ring (because the greatest density of gas in the sphere we see is along the edge) about 2.5 light-years in diameter. Its name comes from the irregular brightness that gives it the appearance of a helix (like a spring) when viewed from the end. With a telescope, it appears as a ghostly smoke ring in Aquarius.

Observing tip: The Helix Nebula has a low surface brightness, so a dark sky is essential. This is a rather large object (slightly smaller than the Full Moon), visible through binoculars, where it looks like a disk. The darker interior is visible with small telescopes.

Spiral galaxies like the Milky Way are full of light-emitting gas clouds, called emission nebulae, that eventually condense to form clusters of stars. These swirls of ionized hydrogen, other elements, and dust are stellar nurseries, resembling the Sun’s birthplace some 4.5 billion years ago.

We see the nearest emission nebula, the Orion Nebula (M42), because it’s illuminated by the Trapezium, a tight group of luminous, hot stars that have formed within it. Their intense radiation makes the gas glow, like a fluorescent lightbulb.

Observing tip: M42, located in the sword of Orion, is visible to the naked eye. If you view through a large telescope, the nebula may appear greenish. The vibrant colors in beautiful photos of this object are too faint for the human eye to register.

The Veil Nebula has many names and several NGC numbers because it takes up nearly 3° of the sky. (By comparison, a Full Moon takes up 0.5°.) It forms a partial ring of ionized gas in Cygnus that shows incredible detail with modest to large apertures under dark skies. The progenitor was a massive star that lit up the night sky when it exploded some 3,000 to 8,000 years ago.

Observing tip: Under a dark sky, the Veil Nebula may be glimpsed with high-quality binoculars. It looks impressive through a wide-field telescope with enough contrast to bear magnification well.Observing tip: Under a dark sky, the Veil Nebula may be glimpsed with high-quality binoculars. It looks impressive through a wide-field telescope with enough contrast to bear magnification well.

Scattered around the Milky Way like mosquitos around a skygazer are spherical groups of stars called globular clusters. Their origin is far different from open clusters, forming at the same time as the galaxy. Some are associated with the cores of dwarf galaxies ripped apart as they collided with the Milky Way. The distance between stars in the cluster may average about 1 light-year, but near the core, they may be only billions of miles apart. (A light-year is about 5.9 trillion miles, or 9.5 trillion kilometers.) 

M4, located close to Antares (Alpha Scorpii), is a favorite of many amateur astronomers for several reasons: It’s easy to find, it’s bright, and its stars can be resolved in telescopes with apertures as small as 6 inches. This ball of stars is 75 light-years in diameter with an estimated age of 12.2 billion years. You are looking at stars nearly three times older than the Sun!

Observing tip: This is one of the easiest globular clusters in the sky to resolve. To spot it, look for a bright bar of stars bisecting the cluster.

The Milky Way is the second-largest member of the Local Group, a cluster consisting of nearly 60 galaxies. Only three galaxies — the Andromeda Galaxy (M31), the Pinwheel Galaxy (M33), and the Milky Way — are large; the rest appear as mere wisps by comparison.

The Andromeda Galaxy is the closest large galaxy. Somewhat bigger than our home galaxy, it spans 220,000 light-years and contains an estimated 1 trillion stars. (For comparison, our galaxy contains 200 to 400 billion stars.) M31 is inclined 18° from edge-on, which intensifies its brightness, just like the Helix Nebula is brightest where we look through its edge. At magnitude 3.5, it can be seen with the naked eye in suburban skies. Under dark skies, Andromeda spans a whopping 3.1°, or roughly the width of six Full Moons.