By the time you read this, we’ll have passed the Autumnal Equinox.
This is the point at which the sun crosses the equator moving from north to south marking fall in the Northern Hemisphere and spring in the Southern Hemisphere. This year the Autumnal Equinox happened on September 22 at 1:02 pm PDT.
Our mid-valley skies are changing too. While the “summer triangle” is still overhead (this triangle is formed by the brightest stars in the constellations of Cygnus (Deneb), Lyra (Vega) and Aquila (Altair)) it is beginning to sink into the west to be replaced by a number of fall constellations (Pegasus, Andromeda, Perseus, Cepheus and Cassiopeia).
The focus of this article is on Andromeda, the daughter of King Cepheus and his wife the vain Queen Cassiopeia. Go outside at about 9 or 10 p.m., face north and high up, to your right (east), you should see the four stars forming the Great Square of Pegasus and, stretching to the north, the constellation of Andromeda.
In the sky it is hard to see Andromeda with her arms outstretched chained to the rocks awaiting Cetus the sea monster sent by Poseidon. Actually, one star in the Great Square’s northeast corner belongs to Andromeda, Alpheratz (Alpha Andromedae) is the brightest star in Andromeda.
The other bright stars in Andromeda are Mirach (Beta Andromedae) and Almach (Gamma Andromedae). Almach is notable because it is a visual (in a telescope) double star. One star is a yellow color and shines at 2.3 magnitude. The second star in the double is blue and shines at magnitude 5.4 (magnitude 1 is the brightest visually and magnitude 6 is the dimmest you can see with your eyes).
Between Mirach and Almach (closer to Almach) is the naked eye visible star (fourth magnitude), Upsilon Andromedae. This star is notable because Upsilon happens to have 4 confirmed planets orbiting it. They are all massive gas giants like Jupiter. The innermost gas giant orbits in about four days (compare this to Mercury which takes 88 days to orbit our Sun).
Finally, the constellation Andromeda also contains the farthest object you can see with just your eyes. This is M31, the Andromeda Galaxy. M31 is 2.5 million light years away from us. When you see M31 your eyes are capturing photons that are 2.5 million years old. How cool is that?
M31 contains about 1 trillion stars and is 200,000 light years across (one light year is about 6 trillion miles). Compare this to our Milky Way Galaxy which contains about 200 – 400 billion stars and is about 100 thousand light years across. M31 is moving towards the Milky Way at about 70 miles per second. In about 3 to 5 billion years M31 and the Milky Way will collide.
M31 and the Milky Way are the largest two galaxies in the Local Group. The local group consists of M31, the Milky Way, M33 (the “pinwheel galaxy”) and about 30 smaller galaxies.
Resource: HVA club
Heart of the Valley Astronomers is a group of amateur astronomers dedicated to sharing our passions for the night sky with the local communities in the central Willamette Valley of Oregon.
We meet on the second Tuesday of each month at the Walnut Community Room located the Scott Zimbrick Memorial Fire Station No. 5, 4950 NW Fair Oaks Drive in Corvallis. Meetings are free and open to everyone.
We also regularly schedule star parties, technical assistance, astronomy classes through Corvallis Parks and Recreation and educational outreach for public and private groups. For more information see www.hvaastronomy.com, or look us up on Facebook.
Question of the Month
Last month: Rank solar eclipses in order of rarity? Answer: Hybrid, total, annular and partial.
This month: What two spacecraft are still going strong after 40 years in space?