This is a special Stargazer Saturday, because it is also International Astronomy Day, and Observe the Moon Night! Visit the Astronomical League website to find an event in your area. (If you are in Denver, visit us at Chamberlin Observatory!)
Tonight after sunset, look to the south-west to see Venus, the brightest planet you’ll see tonight.
Looking south, you’ll see the 48% illuminated crescent moon just 8.5° diagonal to Mars, both in the constellation Sagittarius.
Finally, turn East, North-East to find the constellation Andromeda, and the great Andromeda Galaxy. The Andromeda galaxy is just on the edge of naked eye visibility from a dark location, and would appear as a faint fuzzy patch.
The Andromeda galaxy, also known to astronomers as M31, or Messier 31, is part of our local group of galaxies. It is somewhat larger than our own Milky Way. Up until the early 1900s, it was thought that everything astronomers could see was inside out galaxy. It was Edwin Hubble in 1925 who showed, through the discovery and measurement of a Cepheid variable star in Andromeda, that it was actually much further away than anyone had previously thought, far outside out Galaxy.
Andromeda and the Milky Way are actually approaching each other at a rate of 100km/second! But, given the massive distance between the two galaxies of 2.5 million lightyears, it will take 2.5 billion years for the two to begin a collision and merger.
Observe The Moon Night
With a ~50% illuminated first quarter moon, Saturday provides an excellent time to train a telescope on our natural satellite. Look in particular at the terminator between the illuminated and dark area, where you can see clear shadows and definition in the craters.
To celebrate Observe the Moon Night, we have a special promotion going for new AstroBox subscribers! Sign up with this link, or enter coupon code MOON17 in the month of October, and we will send you a special 12″ inflatable LED moon printed from NASA images! The next AstroBox won’t ship until the first week of December, but for US orders, we will ship your Moon within a few days of your order! (Due to high shipping costs, International customers will receive their moon along with the December AstroBox.) This moon is also available in the Shop for $9.99 + shipping.