by Joe Rao
November 28, 2015
from Space Website

This spectacular image of the Andromeda Galaxy (M31)

was captured by Greg Redfern, the "Sky Guy.”
Credit: Greg Redfern
 

In my opinion - and this of course is purely subjective - the most popular object that people like to view through a telescope is the moon.

Number two is probably the ringed planet Saturn. As far as third place is concerned, I would say it's a toss-up. Everyone enjoys looking at Jupiter, with its complex cloud belts, the famous Great Red Spot and four big satellites.

However, if it's autumn and the sky is reasonably dark and clear, with no bright moon to obscure the fainter stars, then another object makes its way into this conversation:

The great Andromeda galaxy.

Beloved (albeit fuzzy) sky attraction

The following question has floated out of the darkness many times at outdoor star parties I've attended:

"Hey! Can you show us that galaxy?"

"That galaxy" always refers to Andromeda, which is also known as M31 in Charles Messier's famous catalogue of galaxies, nebulae and star clusters. Andromeda is the nearest major galaxy to our own Milky Way, as well as the largest and most massive galaxy in the so-called 'Local Group':

Local Group

Source

The 'Local Group' is the galaxy group that includes the Milky Way.

 

The Local Group comprises more than 54 galaxies, most of them dwarf galaxies. Its gravitational center is located somewhere between the Milky Way and the Andromeda Galaxy.

 

The Local Group covers a diameter of 10 Mly (3.1 Mpc) and has a binary (dumbbell) distribution. The group itself is a part of the larger Laniakea Supercluster (i.e., the Local Supercluster).

 

The local supercluster was previously thought to be the Virgo Supercluster, now an appendage to the newly defined local supercluster.

The two most massive members of the group are,

• the Milky Way galaxy

• the Andromeda galaxy

These two spiral galaxies have each a system of satellite galaxies.

Milky Way's satellite galaxies system comprises,

• Sagittarius Dwarf Galaxy

• Large Magellanic Cloud

• Small Magellanic Cloud

• Canis Major Dwarf

• Ursa Minor Dwarf

• Draco Dwarf

• Carina Dwarf

• Sextans Dwarf

• Sculptor Dwarf

• Fornax Dwarf

• Leo I

• Leo II

• Ursa Major I Dwarf

• Ursa Major II Dwarf,

...plus several additional ultra-faint dwarf spheroidal galaxies.

The Andromeda Galaxy's satellite system consists of,

• Messier 32 (M32)

• Messier 110 (M110)

• NGC 147

• NGC 185

• Andromeda I (And I)

• And II

• And III

• And IV

• And V

• Pegasus dSph (aka And VI)

• Cassiopeia Dwarf (aka And VII)

• And VIII

• And IX

• And X

• And XI

• And XIX

• And XXI

• And XXII,

...plus several additional ultra-faint dwarf spheroidal galaxies.

The Triangulum Galaxy, the third largest and only unbarred spiral galaxy in the Local Group, may or may not be a companion to the Andromeda Galaxy.

 

Pisces Dwarf is equidistant from the Andromeda Galaxy and the Triangulum Galaxy, so it may be a satellite of either.

The membership of NGC 3109, with its companions Sextans A and the Antlia Dwarf, is uncertain due to extreme distances from the center of the Local Group.

The other members of the group are gravitationally secluded from these large subgroups:

• IC 10

• IC 1613

• Phoenix Dwarf

• Leo A

• Tucana Dwarf

• Cetus Dwarf

• Pegasus Dwarf Irregular

• Wolf-Lundmark-Melotte

• Aquarius Dwarf

• Sagittarius Dwarf Irregular

The spiral Andromeda galaxy can be a truly awe-inspiring night-sky sight.

For example, in the second volume of his two-volume autobiography, "In Joy Still Felt" (Doubleday, 1980), the late biochemist and sci-fi author Isaac Asimov described when he and his wife Janet signed up for an astronomy-themed cruise:

"It was a beautiful mild night, and the sky was more splendid than a planetarium dome could have been. Janet used her binoculars to look at the objects described, and the high point came when we saw the Andromeda galaxy for the first time.

 

If the cruise had ended at that point, we would have had our money's worth."

Little cloud, big galaxy

And yet, to the naked eye, Andromeda doesn't look like much - a wispy, hazy blotch that resembles a fuzzy star.

But when you realize exactly what you're looking at, you can forgive the galaxy for being so dim and tired-looking.

The first definitive observation of Andromeda came more than 1,000 years ago. In the year 964 A.D., the Persian astronomer Abd al-Rahman al-Sūfī drew attention to a "little cloud" located among the stars of the constellation Andromeda, the Chained Princess.

Observations by NASA's Spitzer Space Telescope suggest that "little cloud" actually gives off the light of 1 trillion stars - five to 10 times more than our Milky Way possesses. And at its widest, Andromeda is about 220,000 light-years across (the disk of the Milky Way is about 100,000 light-years wide.)

These are indeed impressive figures, but the one factoid that is truly mind-blowing concerns Andromeda's distance - 2.5 million light-years.

The Andromeda galaxy is the farthest object that your eyes can see without the aid of binoculars or a telescope. If you view it tonight (and I'll show you how to find it in a moment), consider that the light from this wispy object traveled 2.5 million years to reach your eyes, traveling all that time at the tremendous velocity of 186,282 miles (299,792 kilometers) per second.

That light therefore began its journey around the time of the dawn of human consciousness, when mastodons and saber-toothed tigers roamed over much of pre-ice-age North America and prehistoric man struggled for existence in what is now the Olduvai Gorge of East Africa.

How to find it

So, how can you spot this beautiful galaxy?

This upcoming week will be a good time to try, because the dazzlingly bright moon that dominated our evening sky this past week is now rising progressively later each evening.

Tonight (Nov. 27), for example, the moon rises at 6:40 p.m. By Nov. 30, it's rising three hours later, and by Dec. 4, it's not up until half-past midnight. So the moon will be less and less of hindrance as the week progresses.

So step outside between 7 and 9 p.m. local time, face south-southwest and look about three-quarters of the way up from the horizon to the point directly overhead. You'll take note of four bright stars; they form the Great Square of Pegasus, one of the landmarks of the sky.

Now imagine that the Square is the bowl of a large dipper, and look for its handle extending out from the star in the upper left corner of the Square. That star is Alpheratz.

Three bright stars form this handle, including Alpheratz. These three - the other two are called Mirach and Almach - are almost evenly spaced and are about as far apart as the stars of the Square itself.

Incidentally,

• Alpheratz

• Mirach

• Almach,

...belong to the constellation Andromeda.

Above the middle star of the handle (Mirach) are two fainter stars nearly in line with it. Near the northern star, if your sky is clear and dark, you can spy a hazy patch of light, almost directly overhead. (If you can't see it with your unaided eyes, use binoculars.)

Focus on Mirach, then scan above it until you find that hazy patch.

And there it is - Andromeda Galaxy...!
 

The darker, the better

The galaxy can actually be a bit of a disappointment through binoculars or a good telescope.

Andromeda often appears as little more than an elongated fuzzy patch, which gradually brightens in the center to a star-like nucleus.

Don't expect to see individual stars; only a long-exposure photograph will bring them out. Once, however, in August 1975, on an exceptionally clear and dark night at the annual Stellafane convention near Springfield, Vermont, I was able to glimpse the galaxy's dark dust lanes through a homemade 6-inch (15 centimeters) "rich field" telescope.

And in very dark skies, one can see the galaxy take on incredible dimensions.

Careful binocular estimates by the French astronomer Robert Jonckheere in the 1950s gave a length of just over 5 degrees and a width of just over 1 degree. For comparison, the "pointer" stars at the end of the Big Dipper's bowl are separated by just over 5 degrees, and the full moon is only 0.5 degrees wide!

Admittedly, to make this measurement, Jonckheere did use "giant" binoculars with 2-inch (5 cm) lenses, with the oculars centered so that both of his pupils were fully used. He also had dark-adapted his eyes for 10 minutes with the exclusion of all light except from Andromeda itself.

The message is clear:

The darker and more transparent the sky, the more impressive the view.

Good luck!