Greetings, stargazers.
Our extra wet end of summer has given way to an extra dry stretch of weather for the leaf changing season. Maybe we will get some good viewing in.
Fall’s evening sky is often thought of as the empty gap between the rich summer Milky Way sky and the bright winter constellations surrounding Orion. In the middle of this large vacant expanse of sky is Pegasus.
Pegasus is the winged horse of mythology. If you use your imagination, you might be able to make out such a pattern in the autumn stars. By far the most prominent part of Pegasus is the asterism called the Great Square. The square is almost 15 degrees on each side, or about one-and-a-half fist-widths. The four corner stars are all between magnitude two and three and can easily be seen with the naked eye.
Right after dusk, the Great Square of Pegasus is in the eastern sky about halfway between the horizon and zenith. The square is tilted about thirty degrees clockwise. A bit later in the evening the square will be very close to zenith, so the orientation depends on which way you are facing.
Although the stars making the square aren’t bright, they are the brightest things around. Other stars inside the square are much dimmer and might not be visible at all in a light-polluted area. I consider the square of Pegasus to be an anchor asterism for this part of the sky. By that, I mean that I use it to find not only the rest of Pegasus, but neighboring constellations, including Andromeda and Pisces.
The northernmost and brightest star of the square is Alpheratz, but this isn’t officially even part of Pegasus. Historically it was shared with the constellation Andromeda. For me to see a horse associated with the square, Andromeda must be the hind legs. Until the early twentieth century Alpheratz had the dual designation of alpha Andromeda and delta Pegasus, but now it is associated exclusively with Andromeda.
Useful links
Comet Tsuchinshan-ATLAS
https://www.astronomy.com/observing/comet-tsuchinshan-atlas-will-soon-move-into-the-evening-sky/
Blaze Star
https://en.wikipedia.org/wiki/T_Coronae_Borealis
Astronomy picture of the day
An Astronomer’s forecast for Durango
http://www.cleardarksky.com/c/DrngoCOkey.html?1
Old Fort Lewis Observatory
http://www.fortlewis.edu/observatory
hakes_c@fortlewis.edu
Comet Tsuchinshan-ATLAS will be making an appearance in the evening sky after sunset this month. Although it is easily bright enough to be seen by the naked eye, it is close to the sun, so the best time to see it will be right after sunset low in the western sky. Unfortunately for comet-viewing we are approaching the full moon, so for the next week or so that will also interfere with the best views. It might become easier to see later in the month, but predicting the brightness of comets is notoriously unreliable.
Venus, the evening star, is getting farther out from behind the sun, so it stays above the horizon a bit longer in the western sky after sunset.
Saturn is in the best position of the year for viewing through a telescope. If you haven’t ever seen Saturn that way, this is a time to try to do that. Through a good pair of binoculars some people can tell the bright dot looks more like a football than a soccer ball. You do need more magnification to see the separation between the planet and the rings. The rings are getting harder to see every month, and in March of next year they will completely disappear from our perspective as they align with our view from Earth. They won’t get back to their maximum tilt until 2032.
The expected nova of T Coronae Borealis, the Blaze Star, still hasn’t happened as of this writing. Unfortunately, the constellation Corona Borealis is setting earlier in the evening every night. We have taken magnitude measurements several times in hopes of getting before-and-after pictures of the event. However, things this low in the western sky are inconvenient to observe with the permanently-mounted telescope in the roll-off roof observatory at Fort Lewis College.
Charles Hakes teaches in the physics and engineering department at Fort Lewis College and is the director of the Fort Lewis Observatory.
