Saturday, October 9, 2021, is this fall’s Astronomy Day! Here are some easy way to explore the sky.

What is Astronomy Day?

Doug Berger, while president of the Astronomical Association of Northern California at the time, started Astronomy Day in 1973 with the goal of bringing attention to the night sky. Astronomy Day happens every spring and fall on a Saturday close to the first-quarter Moon. This month, the Moon reaches first quarter on Wednesday, October 13th (October 12th for U.S. time zones).

Whether you have a telescope, binoculars, or prefer to observe with only your unaided eye, this is a great chance to head out and see some amazing things in the night sky this weekend.

Star parties, where people bring their equipment and observe together, are a great way to spend the night. These events are an inspiring experience for anyone, including beginners who are just starting to learn about astronomy.

Unfortunately, COVID-19 is still making things difficult, and many of us can’t get to events easily. Instead, how about having a virtual star party? Talk to some friends or with a local astronomy club, chat online, and enjoy all things astronomical this weekend.

Here are a few things to get you started, especially if you’re new to the hobby.

The Sun

It is Astronomy Day isn’t it? Why should everything happen at night? So, a few times during the day, note where the Sun is. That path the Sun travels across the sky is called the ecliptic, which will come in handy later.

IMPORTANT: Please, no telescopes or binoculars for this. You could severely damage your eyes. Do not stare at the Sun, lenses or not.

The Moon and Venus

In the dimming autumn evening, let’s look for our nearest celestial neighbor: the Moon. On Saturday after sunset, in deepening twilight, we'll see a young, waxing crescent Moon, about halfway between new and first quarter, just above the stunning gleam of the planet Venus. As the pair glide toward the horizon, let’s see if we can spot earthshine, the sunlight that bounced off Earth, off the Moon, and back to our eyes. Earthshine appears a dim glow on the Moon’s unlit side, and it’s easiest to see during the Moon’s crescent phases. Maybe we can also catch some of the Moon’s features hiding in the shadows there. The pair will set about two hours after sunset, so linger here for awhile; it’ll be worth it.

Planets along the ecliptic
Follow the ecliptic from the Moon and Venus toward Saturn and Jupiter on October 9th.

Saturn and Jupiter

Remember when we were watching the Sun’s movement across the sky and used it to imagine the ecliptic? After catching up with the Moon and Venus, follow that same imaginary line back toward the east across the southern sky. The next bright object we’ll come to is the planet Saturn.

I won’t lie, Saturn’s a little tough. It’s not as bright as we might expect it to be; after all, its light has traveled almost 2 billion miles to get to our eyes! Still, I always love how understated and subtle it is with the naked eye. Binoculars likely won’t let you see the rings, but their presence makes the planet appear a bit stretched out and egg-shaped. With a telescope, those rings come into clearer view. With optical aid, you might even be able to see its giant moon, Titan, appearing as a nearby star. (You can double-check using our interactive online tool.)

A bit farther to the east, we’ll find unmistakable Jupiter. It’s the third-brightest object in the night sky (after the Moon and Venus), and it’s been positively gorgeous recently. With our binoculars, we can spot its four planet-size “Galilean” moons: Io, Europa, Ganymede, and Callisto. Those tiny dots are each very roughly the size of Mercury.

Jupiter and its Galilean moons
A glimpse of Jupiter and the Galilean moons

The Pleiades

As the night goes on, we’ll see the Pleiades open star cluster (Messier 45) rise. The Pleiades, which looks like a tiny dipper, but isn’t the famous Little Dipper, is 444 light-years from us. This makes it one of the closest open star clusters to Earth. With good vision and sufficiently dark skies, we might be able to see six or seven stars with the naked eye. Through binoculars, though, it’s positively jaw-dropping, with countless stars spilled across the sky. We usually think of this cluster as a wintertime object, but here it is in early October: a sneak preview of good things to come.

Pleiades on the sky
The Pleiades in the late evening, when they're high in the eastern sky, on October 9th.
Stellarium, with additions by the author

The Andromeda Galaxy

This one’s a bit of a challenge for beginners. The Andromeda Galaxy (Messier 31) is the nearest large spiral galaxy, and in October, it’s well-placed for easy spotting in mid-evening. While it’s possible to see M31 under very dark and clear skies, most of us need binoculars or a telescope to find it.

There are two easy ways to get to it. First, face northeast and find the constellation Cassiopeia. This month, its stars sit like the number “3” in the northeast sky. Then scan the sky about 15 degrees toward the right or upper right. (Extend your fist and stick out your index and pinkie fingers in a “hang loose” sign, and it’ll be that far toward the right of Cassiopeia if you’re in the Northern Hemisphere ).

Or you can star-hop with a telescope or binoculars. Start by finding Mirach, which is the second in the line of three stars extending northeast from northeastern corner of the Great Square of Pegasus. From Mirach, hop toward the northwest to Mu Andromedae, then to Nu Andromedae (see diagram below), and start scanning the sky nearby.

Either way, you’ll know when you see it because the galaxy almost looks like a giant thumbprint on the sky. This is a great skill to pick up because once we find it, we’ll know exactly where to look next time, and then we can tell everyone where they can see 2.5 million-year-old light, too.

How to find M31
Use the stars of the Cassiopeia and Andromeda constellations to find the Andromeda Galaxy
Stellarium, with additions from the author

These are just a few things we can see this weekend. What else should we look for? I hope you’ll head out and have a great Astronomy Day, everyone! Leave a comment and let me know how it goes!


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