The Night Sky – CELESTIAL SPECTACLES OF NOVEMBER
Hello, I’m Darrell Heath of the UALR College of Arts, Letters, and Sciences; welcome to The Night Sky.
Now that we are well into fall you should be outside taking advantage of the cooler weather and longer nights available for stargazing. With the cooler weather you don’t have to fight off all those annoying mosquitos and the less haze and humidity we have, the better the viewing.
With this increase in the clarity of our skies there comes the question of just how far can you see with your unaided eye? If we are talking about terrestrial viewing then the answer depends on things like how good your eyesight is, your elevation, and how much light a distant object is either reflecting or emitting and how large it is. The Earth’s surface curves out of sight at about 3 miles but if you were high atop a mountain you might be able to see bright city lights hundreds of miles away. With really acute vision and dark conditions some people can even see a candle flame 30 miles away. The human eye is very sensitive to light and when we look up at the night sky we can see objects even further away.
Standing under a very dark sky you can look up and see several thousand stars at any one time and they are all well within 1,000 light years of Earth, with each light year equaling about 6 trillion miles. All of the stars you see are found within our own Milky Way Galaxy, which is home to several hundred billion stars in all.
So, on average you are probably seeing stars that are actually only a few tens to a few hundred light years away. But what if I were to tell you that, without any kind of optical aid, that you can see something that is much, much further away? You can, and it’s called the Andromeda Galaxy and it is some 2.5 MILLION light years away.
The Andromeda Galaxy lies within the constellation of Andromeda and according to Greek mythology she was the unfortunate maiden who was to be sacrificed to the sea monster Cetus in order to appease the wrath of the God Poseidon. But don’t worry; the story has a happy ending as the hero Perseus happened along at just the right time to save her from becoming lunch for a sea monster
Ok, here’s how you can find the Andromeda Galaxy. Just step outside on a dark, moonless night in November and face towards the southeast at around 9PM. Remember, the darker your sky, the better the viewing will be.
First, we are going to look for the Great Square of Pegasus, a pattern of stars that make up the main body of the flying horse. Incidentally, in some versions of the myth it was Pegasus that provided the getaway method for Andromeda and Perseus after our hero killed Cetus.
The Great Square is high upon the southeastern sky in November and is made up of four bright stars that are all roughly the same brightness; say about 2nd and 3rd magnitude. To give you an idea of how large the square is, each of the four corner stars is about 15 degrees apart from each other. Fifteen degrees is the distance between your first and little fingers spread apart and held out at arms length. The Great Square of Pegasus is called “Great” for good reason: it’s one of the largest star patterns in our sky.
Once you’ve located the square we now need to look to the star that forms the top left, or northeast, corner of the square. This star does not actually belong to the constellation of Pegasus, its name is Alpheratz and it represents the head of Andromeda.
OK, we are almost there. From Alpheratz you will look for two, curving lines of stars that branch off from it and trails away towards the north. This trail of stars represents the reclined body of Andromeda. At this point you should be looking almost directly overhead. Now we are going to let our eye travel along the lower string of stars until we reach the brightest one within the strand, Mirach, located about midway along the string. Draw an imaginary line from Mirach and through the fainter star just above it, which is known as Mu Andromedae and then just a little ways beyond Mu to the Andromeda Galaxy. Your imaginary line from Mirach to the galaxy should be about 10 degrees, or the width of your fist held out at arm’s length.
To the naked eye the Andromeda Galaxy looks like a fuzzy, elliptical patch on the sky. The darker your sky the more pronounced and larger the galaxy will appear. You are looking at the most distant object the naked eye can perceive. And at 2.5 million light years away the light that is now entering your eye as you gaze upon it first left the galaxy when our ancient human ancestors were wandering across the plains of eastern and southern Africa.
But don’t stop with just the unaided eye; use a pair of binoculars to get a better look. With their wide field of view, binoculars are able to take in much more of the galaxy than would the more narrower field of view provided by most telescope eyepieces. Viewing with binoculars from a moderately light polluted sky will definitely show the faint glow of the galaxy’s elliptically shaped core. The Andromeda Galaxy is so big that, under dark sky conditions, you will see that it takes up about 3 to 5 degrees upon the sky, or more than half the field of view in your binoculars.
An even better way to appreciate the full grandeur of this galaxy is through photography. Just take a look at this image of the Andromeda Galaxy taken by Central Arkansas Astronomical Society member John Reed from here in Central Arkansas during October of 2014. Not only does the photo reveal the galaxy’s beautiful spiral structure and dark dust lanes, it also shows us two smaller satellite galaxies: Messier 110 in the upper left and Messier 32 just left of center.
And yes, the Milky Way and Andromeda galaxies are destined for a fender bender of cosmic proportions. Some four billion years from now the two galaxies will collide and merge to form a single galaxy. If any humans are still around at this time perhaps they will call they new galaxy “Milkomeda”. Such galactic mergers are not at all uncommon and are how most galaxies evolve over time. You might think that the stars within the galaxies would also collide with one another but due to the vast distances that separate individual stars such collisions are actually very, very rare.
While a collision of two galaxies is indeed a celestial spectacle they happen over very long periods of time, say, on the order of many millions of years. However, we have another spectacle happening in November that you can witness over just a few hours: a meteor shower. On the night of November 17th the Leonid Meteor shower will reach its peak. While folks in Europe are better situated this year for observing the shower those of us here in the states can expect to see at least a handful of meteors throughout the evening. The source of the shower is the bits of debris produced from the passage of Comet 55P/Temple-Tuttle. When Earth slams into this debris field the dust-sized particles enter our atmosphere at speeds of up to 160,000 miles per hour, creating superheated, glowing columns of air that we perceive as meteor streaks. Sometimes you will likely see larger pieces of comet debris, about the size of a pea, that will create fireballs across the sky that are brighter than the planet Venus and even casting shadows upon the ground.
We can never really predict the number of meteors that the Leonids will produce. On average it is usually just a handful per hour but in the years 1833, 1866. 1966, and in 2001 they have been known to produce meteor storms of thousands per hour. Most astronomers think the Earth will not pass through a dense debris field until the year 2099. Still, any meteor shower is worth your time and this year, a waning crescent moon will not interfere with the viewing. Just find yourself a good, dark sky to observe from and step outside to face east after dark. Look between the horizon and overhead and let your eyes roam around the sky. The peak times in our area will not occur until after midnight when the radiant is high up in the sky. The radiant is the area on the sky where the meteors all seem to originate from (in this case in the constellation of Leo, the Lion). So, the time to see the most meteors will be from midnight until dawn of November 17th and 18th.
Our night sky is always filled with celestial spectacles of one sort or another and this is just two to be on the look out for in November. Be sure and visit The Night Sky’s new web site for announcements about others in our news section.
Until next time, I encourage you to get outside, look up, and wonder.