The Deep Sky

FAS Astronomers Blog, Volume 30, Number 8.

When most of us start out in astronomy, we usually focus first on learning the Night Sky. This is followed by the purchase of a telescope and a few backyard sessions spent looking at the Moon and planets. Then we might follow by observing a few stars. However, as our stargazing skills sharpen, and our telescopes become larger, many of us begin searching for deep sky objects.

For most amateur astronomers, the definitive list of deep sky objects was created back in the late 1700s by Charles Messier. You can find a few notes about him and his catalog in the article The Great Debate. The modern Messier catalog contains 109 distinct objects (M1-M110), taking into consideration the possible duplication of M101 and M102.

Other catalogs have been developed over the years.

• In 1995, Patrick Moore expanded on Messier’s catalog with the Caldwell Catalog, which contains an additional 109 objects not included in Messier’s list (C1-C109).
• William, Caroline, and John Herschel compiled an extensive list of over 5,000 objects in the late 1700s. Herschel’s 400 object deep sky catalog is a subset of this list and provides amateur astronomers with more challenging objects than those in the Messier and Caldwell catalogs.
• John Louis Emil Dreyer produced the New General Catalog (NGC) in 1888 followed by two index catalog supplements (IC) in 1895 and 1909. Dreyer’s NGC/IC catalogs are still in use today and NGC numbers are commonly used to identify many deep sky objects.
• Philibert J. Melotte, (Mel #) in 1915, and Per Collinder, (Cr #) in 1931, created two catalogs of open star clusters.

Most of the Messier objects along with a few others can be found using an amateur-sized telescope. The challenge is to be patient and know where to look. Below is a summary of several of these objects. If you need some help, the folks at freestarcharts.com have some nice finder charts. You can also use the constellation charts provided by Sky & Telescope and the IAU. The book Turn Left at Orion is another good reference.

To set your expectations, these objects will NOT appear in glorious color. Our eyes are just not sensitive enough. With small amateur telescopes, fuzzy black and white objects are the best we can see. For most of these, the challenge (and fun) is to find them in the night sky, and fuzzy or not, see them live!

Also, not all these objects are visible for the entire year. For some, you might have to wait for the appropriate season.

Most of the easy to spot deep-sky objects are classified into the following categories.

• Open Star Clusters are small and younger clusters of stars that formed at approximately the same time.
• Globular Star Clusters are larger and older clusters of stars found outside the plane of the Milky Way. These clusters are over 10 billion years old and contain hundreds of thousands to millions of stars.
• Nebulae are gaseous clouds, typically composed mostly of hydrogen, where new stars are being formed. Although at least one, the crab nebula, is a supernova remnant.
• Planetary Nebulae are the remnants of stars after they expanded into a red giant where material was blown away from the surviving star core.
• Galaxies are large collections of stars such as the Milky Way and Andromeda.

It isn’t easy to describe the location of an object in the night sky with just words. Depending on the time of night or year and your orientation (looking north or south), constellations can appear right side up or upside down. So, for consistency, the directions below assume a constellation (and the figure it represents) is viewed right side up unless otherwise noted.

The Winter Circle

The easiest Messier object to find is the Pleiades (aka the Seven Sisters and Subaru) [M45]. It is an open star cluster siting on the back of Taurus the Bull. Many people mistake the Pleiades for the little dipper, due to its four brighter stars that form a bowl and a fifth star representing a handle. The Pleiades is also an ancient eye chart. The more stars you can discern with your naked eyes, the better your vision.

The Hyades (Hi a dees) [C41] is an expansive open cluster covering the V that makes up Taurus’s head and then some. It is one of the closest open clusters to the Earth at only around 150 light years away. The bright star Aldebaran appears to be within the Hyades, but it is closer to us at around half the distance.

A more challenging object, because of its low magnitude, is the supernova remnant the Crab Nebula [M1]. It is found near the star Tianguan/Zeta Tauri (the lower horn of Taurus), and roughly in the direction of Elnath (the other horn).

One of my favorites and another object visible to the naked eye is the Orion Nebula [M42]. The nebula is the middle object in Orion’s sword. Look very closely and see if you can find the Trapezium, an asterism consisting of four bright stars at the center of the nebula.

The Rosetta Nebula [C49, NGC 2237] along with an open cluster [C50, NGC 2244] at its center are found in the constellation Monoceros around 2/5^th of the way from Betelgeuse toward Procyon.

Two very challenging nebulas in Orion are the Horsehead Nebula (found below Alnitak on the line toward Saiph) and the Flame Nebula (found just above Alnitak and outside the line toward Betelgeuse).

Gemini’s only Messier object is an open cluster [M35], which is found out from and just above the left foot of Castor (Tejat/Mu Geminorum and Propus/Eta Geminorum). It is a bit farther from Propus than the distance between Tejat and Propus. It is also ½ way between Alhena/Gamma Geminorum (3^rd brightest star in Gemini and left foot of Pollux) and Elnath (the horn of Taurus).

An open cluster [M41] is found in the lower front of the dog’s body near Sirius in Canis Major. You might be able to pick out a variety of stellar colors in this cluster.

Springtime

Cancer is one of the fainter constellations in the night sky. It looks like an upside-down Y and is found between Gemini and Leo. Its most interesting object is the Beehive Cluster [M44]. The cluster is found ½ way between Asellus Australis/Delta Cancri (the intersection of the Y) and Asellus Borealis/Gamma Cancri (the next bright star above the intersection), and a bit to the right in the direction of Pollux.

The Coma Star Cluster is an open cluster in the constellation Coma Berenices somewhat similar to the Hyades. It is relatively near us and spread out so that it is best viewed with low power binoculars. Although Ptolemy cataloged it, it is not included in either Messier’s list or the NGC/IC catalogs. It is included in Melotte’s 1915 Catalog [Melotte 111]. To locate this cluster, use Leo as your guide. Follow a line from Regulus through Zosma/Delta Leonis (the upper star of Leo’s triangle). Continue about the same distance to the cluster.

Hercules

For these directions, we assume Hercules is upside down as it appears when viewing it when looking south. Another one of my favorite objects is the Hercules Globular Cluster [M13]. This is the brightest globular cluster visible from the Northern Hemisphere. It is found on the side of the Hercules Keystone facing away from Vega and toward Arcturus and Corona Borealis. It is approximately 1/3 of the way down from Eta Herculis (the corner of the Keystone near his “kneeling leg”) and toward Zeta Herculis A (the lower right corner of the Keystone).

There is another globular cluster [M92] found in the constellation Hercules. It is located approximately ½ of the way between the top middle of the keystone (between Pi Herculis and Eta Herculis) and Iota Herculis (near the head of Draco).

Scorpius/Sagittarius

There are several objects in and around Scorpius and Sagittarius (aka the “teapot”). To find them use these stars.

• Shaula/Lambda Scorpii, the Scorpion’s “stinger”.
• Kaus Media/Delta Sagittarii, the upper right corner of the teapot.
• Phi Sagittarii, the upper left corner of the teapot.
• Nunki/Sigma Sagittarii, the top outside of Sagittarius’ handle.
• Kaus Borealis/Lambda Sagittarii, the tip of the teapot’s lid.
• Alnasi/Gamma Sagittarii, the tip of the “spout” of the Sagittarius teapot”.

The Ptolemy Cluster [M7] is between the constellations Scorpius and Sagittarius. It is around ½ way between Shaula and Alnasi. The Butterfly Cluster [M6] is close by The Ptolemy Cluster. Draw a line from Nunki to Kaus Media. Extend it out the same distance and just below Alnasi toward Scorpius.

The Lagoon Nebula [M8] is to the right and above the teapot lid. Draw a line from Nunki to Kaus Borealis and extend it out about the same distance to the nebula. The Trifid Nebula [M20] is just above the Lagoon Nebula. To find it, draw a line from Kaus Media through the Lagoon Nebula and extend it just a bit further and slightly to the left.

Well above Kaus Borealis is an open cluster [M25], the Swan/Omega Nebula [M17] and the Eagle Nebula [M16]. Draw a vertical line perpendicular to the base of the teapot and Phi Sagittarius. Extend it around two times to M25, three times to the Omega Nebula, and 3 ½ times to the Eagle Nebula.

A globular cluster [M22] is found to the left of Kaus Borealis and above Phi Sagittarii. A smaller globular cluster [M28] is found above and just to the right of the Kaus Borealis.

The Summer Triangle

The Ring Nebula [M57] is a planetary nebula found between Sulafat/Gamma Lyrae and Sheliak/Beta Lyrae (the two bottom stars of Lyra the Lyre/Harp). Despite its low magnitude, it can be found with a small telescope.

The Dumbbell Nebula [M27] is a planetary nebula resembling a dumbbell found in the constellation Vulpecula. This constellation is very difficult to find, so draw a line from Rotanev/Beta Delphini (right star of the Daphnis “diamond”) toward Albireo (the head of Cygnus). The nebula is just over ½ way between the two. It is also just above and ¼ of the way on a line from Eta Sagittae (the point of Sagitta’s arrow) toward Albireo.

The Wild Duck Cluster [M11] is an open cluster Shaped like a V (flock of ducks). This one might also be challenging to find. It is technically found in the constellation Scutum but use Aquila to find it. Draw a line from Altair to Delta Aquilae (what might be considered the bottom of a diamond forming Aquila). Extend the line around 1 ¼ times farther to the cluster. It is down and just to the right of Lambda Aquilae (the end of Aquila’s tail).

The Cooling Tower Cluster [M29] (not shown in the diagram below) is just off to the right of Sadr and near the right wing of Cygnus. Follow the right wing for a very short distance and then slightly forward toward Albireo.

Three more difficult objects (not shown on the diagram below) can be found around the constellation Cygnus.

• Not too far from the star Deneb is the North American Nebula [C20 / NGC 7000] with the distinct Cygnus Wall.
• Between the North American Nebula and Deneb and slightly toward Albireo is the Pelican Nebula [IC 5070].
• Near the right wing of Cygnus is the Eastern Veil Nebula [C33 / NGC 6992] and Western Veil Nebula [C34 / NGC 6960].
• Near the star Sadr at the center of the Northern Cross and toward Albireo is the Crescent Nebula [C27 / NGC 6888].

Pegasus

For these directions, we assume Pegasus is upside down. To the right and just above the star Enif (the nose of Pegasus) is another globular cluster [M15]. Draw a line from Baham/Theta Pegasi (the intersection of the neck and head of Pegasus) to Enif and extend it out just under ½ the distance to the cluster.

Another object just barely visible without binoculars or a telescope is the Andromeda Galaxy [M31]. It will appear as a fuzzy patch of light, but through a telescope from a dark sky location you might see the brighter central portion of the galaxy. To find it:

1. Start with Alpheratz (the star in the upper left corner of the Great Square of Pegasus – as it appears when looking south).
2. Hop one-two left across the bottom row of the Andromeda constellation through Delta Andromedae to the star Mirach.
3. Then hop up one-two through Mu Andromedae to find the galaxy.

Below Mirach, around the same distance as to Andromeda, but in the opposite direction is the Triangulum Galaxy [M33]. It is technically in the constellation Triangulum – hence its name. Although a bright galaxy, it is somewhat diffuse, so it might be difficult to see.

For more of a challenge, try to locate the globular cluster [M2] below the head of Pegasus in Aquarius.

• Draw a line from Markab/Alpha Pegasi (the lower right corner of the Pegasus great square) through Baham/Theta Pegasi (the intersection of the neck and head of Pegasus). Extend it around ¾ of the distance to the cluster.
• You can also use the top of the constellation Aquarius, which has four stars that make up a “squiggly” shape. Draw a line from Eta Aquarii (the left star) through Sadalmelik/Alpha Aquarii (the right star) and extend it roughly the same distance to the cluster.

Perseus/Cassiopeia

The Perseus Double Cluster [C14, NGC 869 and NGC 884] is a Caldwell object worth looking for between Perseus and Cassiopeia.

• Draw a line from Al Fakhbir/Gamma Persei (left base of the triangle at the top of Perseus) through Ruchbah and Navi (the two stars marking the left middle of Cassiopeia’s W or right middle of Cassiopeia’s M). The Double Cluster is halfway between Al Fakhbir and Ruchbah.
• Or draw a line from Navi and Ruchbah through Mirfak (the intersection of the Perseus upside-down Y and brightest star in Perseus). The Double Cluster is around 1/3 of the way from Ruchbah to Mirfak.

Two open clusters are found around Perseus.

• The Perseus Open Cluster [M34] is located just a bit toward Perseus from the middle of the line between Algol (lower right end of the Perseus upside down Y) and Almach (end of the lower row of Andromeda).
• The Alpha Persei Cluster [Mel 20] is a wide cluster surrounding the star Mirfak.

One of the more interesting open clusters, and another Caldwell object, is the ET/Owl Cluster [C13, NGC 457] found near Cassiopeia. You can see two bright stars for its eyes, two stars for its feet, a row of stars representing its body, and several stars off in either direction for its arms. Many think it looks like an extra-terrestrial (ET) or an owl.

• It can be found by drawing a line (the left of Cassiopeia’s W or right of Cassiopeia’s M) from Segin to Ruchbah and extending it half that distance. The cluster is just off the line toward Andromeda and Perseus.
• You can also draw a line from Navi (the center star of the W or M) that intersects with the above line to create a right angle near the cluster.

The Big Dipper

Galaxies, other than Andromeda, are more distant and harder to find. For these, you will probably need dark skies and a larger telescope. The Whirlpool Galaxy [M51] might be one to search for. It is technically in the constellation Canes Venatici but is just under the tip of the handle of the Big Dipper (Ursa Major).

• Draw a line through the bottom of the bowl (Merak to Phecda). Extend it out twice the length. The galaxy is just a bit toward the handle and the star Alkaid.
• You can also draw a right triangle with Mizar (middle star in the handle of the Big Dipper) and Alkaid (the end of the handle of the Big Dipper) as the hypotonus. The Whirlpool Galaxy is just beyond the line from Mizar through the right-angle vertex.

Two other galaxies, Bode’s galaxy [M81] and the Cigar galaxy [M82], are found in Ursa Major by drawing a line from Phecda (lower inner star of the Big Dipper’s bowl) through Dubhe (upper outer star of the bowl) and extending it the same distance to the galaxies.

The End

For a little more adventure, the folks at Astronomy Magazine have a “mini-Messier marathon” you might try with some of these objects.

To find these deep sky objects, you might also use one of the many astronomy apps available for smart phones and tablets. Most have augmented reality, which allows you to hold the phone or tablet up and the app will show you the portion of the sky you’re looking at. Sky Guide, SkySafari, and Star Chart are three that I use.