Some Autumn Binocular Sights

By Bob Moler

Note: This was the article in the October 2018 issue of the Grand Traverse Astronomical Society newsletter the Stellar Sentinel.

Our October 2018 meeting will be devoted to telescopes of all kinds. Just in time for holiday giving. Selecting the right telescope and mount is the key to the enjoyment of the heavens.

Often overlooked are binoculars. These handheld low power telescopes are great for land and sky viewing. With the added advantage of allowing one to learn the stars and constellations. There are no go-to binoculars. And besides, learning the constellations and their stories is an enjoyable pastime that will reward one for a lifetime. It certainly has mine.

Binoculars are gauged by two numbers, like 7X35 or 10X50, or 8X30. The first number is the magnification, how large the image is over the naked eye. The second number is the aperture (diameter of the front lens) in millimeters. The larger the aperture the more light gets in. Binoculars having more than 10 power are hard to hold steady, and some allow a mount that can be connected to a photographic tripod.

So what can you see with binoculars? Here are some binocular objects visible in autumn.

The Great Andromeda Galaxy

The Great Andromeda Galaxy is the closest large galaxy to us in the Milky Way. It’s actually a bit large than our galaxy. And in 4 billion years, give or take, it will collide with the Milky Way. Right now it is the farthest object visible to the naked eye at two and a half million light years away. To the naked eye it is just a small smudge of light. In binoculars it appears as a narrow spindle of light.

My way of finding it starts with the Great Square of Pegasus the upside down flying horse of Greek myth. This month it is in the east and the square is poised on one corner. The leftmost stars is named Alpheratz, and actually belongs to Andromeda. Follow two stars to the left, and then go two stars up. Above right of this last star is the galaxy.

Alpha Persei Association

Below the W shaped constellation of Cassiopeia in the northeast is the constellation of Perseus the hero. To me it looks like the cartoon roadrunner, or a misshapen Greek letter  (pi). On the top of pi or the back of the roadrunner is the constellation’s brightest star Mirfak, Bayer catalog designation Alpha Persei. There’s a few naked eye stars around Mirfak, but in binoculars there are many stars scattered around Mirfak just under naked eye visibility. It is a very loose star cluster, so it’s called an association instead. It is about 600 light years away.


The Pleiades and Hyades

The Pleiades or Seven Sisters is a beautiful star cluster that is seen later in the evening in October low in the northeast under Perseus. For those with good eyesight six stars can be seen. What of the seventh, the Lost Plead? Anyway in binoculars this star cluster shows many more than 7 stars. It is a beautiful group with the brightest stars being almost arc white hot, tinged with blue, at least to my eyes. The Pleiades are young, the stars here are perhaps only 100 million years old. They about 444 light years away. The Pleiades are located in the shoulder of Taurus the Bull.

Below them and rising about an hour later is the V shape of stars that is the face of Taurus the Bull, with the bright red star Aldebaran as his angry red eye. The V of stars in binoculars is the star cluster called the Hyades. Aldebaran is not part of the cluster, it is about half the distance to the Hyades. The stars of the Hyades are more spread out, partially because it is less than half as far away as the Pleiades at 153 light years. Its stars are about 625 million years old, the brightest of them have all since died, and the cluster is dispersing. The Hyades is an important star cluster because it is the closest and withing reach of the direct measurement by parallax before space based measurements with the Hipparcos and Gaia satellites.


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Updated: 09/30/18