October Podcast: The Moon’s Waxing and Waning

This episode is sponsored by Celestron, manufacturer of high-quality telescopes and an industry leader in developing exciting optical products with revolutionary technologies.

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The Moon’s phases are in sync with the calendar this month. We start October with a New Moon on the 2nd. During the next week, a thin crescent appears low in the southwestern evening sky and waxes (gets a little fatter) as it climbs higher night by night. This waxing continues until full Moon on the 17th, known traditionally as the full Hunter’s Moon. After that the sunlit portion of the Moon wanes (gets thinner and thinner) as it approaches new Moon.

It’s easy to think of the Moon as just a circle in the sky, but it’s really a sphere. And if you’ve ever wondered why the Moon shows different phases as it orbits around Earth, here’s something you can try with a golf ball or a ping-pong ball. Go outside just before sunset in early October, and find the crescent Moon over in the southwest. Hold the ball up at arm’s length so it’s pointed in the Moon’s direction and in sunlight. Now look at the ball. You’ll see a slice of it on the right side illuminated by the Sun, in a crescent shape, while most of it is in shadow — exactly how the Moon looks!

Do this a couple of nights later, again just before sunset, and you’ll notice that the Moon has moved around in its orbit and appears farther east. Point your ball toward the Moon, and its surface will look more fully sunlit than it did before. It’s waxing, just like the Moon is. The ball and the Moon both show these different shapes because they’re spheres being illuminated by the Sun from different angles.

Meanwhile, four bright planets await you over the course of October evenings. To start your search, you’ll need a viewing location with a completely clear view toward west — no trees, no buildings, no clouds along the horizon in that direction. Watch where the Sun sets, and about 45 minutes later look off to the left (close to the horizon) for brilliant Venus.

As twilight dims, turn to face east, where Saturn has been a steady presence for the past couple of months. Jupiter and Mars trail behind Saturn in the sky right now. Jupiter will be unmistakably bright once it climbs over the eastern horizon. That occurs around midnight early in October but by 10 pm at month’s end. Mars comes up a couple of hours later, situated to the right of the stars Castor and Pollux in Gemini and to the left of Orion, all rising together in the east.

Now if you like a bit of a stargazing challenge, right now there’s a comet cruising through the inner solar system named Tsuchinshan-ATLAS and designated C/2023 A3. October will offer your best chance to spot this interloper, and with luck it’ll become bright enough to see by eye! For tips on where and when to spot it, listen to this month’s Sky Tour Podcast.

And in October’s episode I also describe two huge celestial beasts that are now in view: Pegasus, the Winged Horse, and Ursa Major, the Big Bear. Pegasus is rearing up in the east as it gets dark. Look for this constellation’s Great Square, tipped up on one corner, which represents the body of this mythical horse. Over in the north is our old friend, the Big Dipper, which is just a part of the Great Bear. The bear’s pointy nose, marked by the star Muscida, is about two fists to the right of the Dipper’s bowl. The bear’s legs dangle underneath, and the farther north you are the more of them you’ll see. Its tail is marked by the arc of three stars in the Dipper’s handle.

There’s lots more to discover overhead during October nights, and you can track it all down using this month’s episode of the Sky Tour astronomy podcast. Use it to find everything described here — plus a lovely assortment of easy-to-spot stars and constellations.

Read the full podcast transcript.