Full moon

Minnesota Skies: October 2020

Your local guide to observing celestial objects and events

Published09/25/2020 , by Deane Morrison and Thaddeus

October begins and ends with a full Moon.

The first rises the evening of October 1, only about three hours past the exact moment of fullness. Following it into the eastern sky is Mars, now too bright to be washed out by any lunar luster. Over to the south, brilliant Jupiter and dimmer Saturn are drawing nearer, en route to a close encounter in December.

The night of October 2, Mars and the waning Moon rise and travel the night sky together. On October 13, Earth laps Mars in the orbital race, passing a mere 38.6 million miles from the red planet. That night Mars shines down from the constellation Pisces, where no bright stars will be close enough to rival its splendor.

Above and slightly west of Mars, the Great Square of Pegasus is now in prime viewing position. Look below it on a moonless night and see if you can find the ringlike Circlet of Pisces, representing one of two fishes in the constellation.

In the predawn sky, Venus dazzles in the east. Watch the bright star Regulus, in Leo, the lion, glide by the planet early in the month, passing closest on the October 2 and 3. On October 13 and 14, waning crescent Moons join Venus. All month long, look off to the west of Venus to see brilliant Sirius shining from its berth in Canis Major, the big dog. This year October and November give us a great chance to compare Venus, the brightest planet, with Sirius, the brightest star in the night sky. But it will be easier this month because the two will be closer.

October’s second full Moon shines the night of the 30–31. The second full Moon in a month is often called a blue Moon, but the original definition was the third of four full Moons occurring in a single season. By that definition, we’ll see our next blue Moon on August 22, 2021.

October bids farewell with Halloween, an astronomically based holiday. To the ancient Celts it was known as Samhain, one of four cross-quarter days falling midway between an equinox and a solstice. It began at sundown on October 31, when all the evil spirits that had been cooped up since May Day were released to wreak havoc on humankind. People lit lanterns in gourds to ward them off and left food offerings to appease them—traditions that survive in jack o’ lanterns and trick-or-treating.

Deep Sky Objects

Thanks to the earlier sunset, the Milky Way is still visible for a couple of hours in the early evening. But as the night goes along, more and more of the sky away from the Milky Way is available for observing. To the unaided eye, the parts of the sky on either side of the main disc of the Milky Way are filled with stars that are still part of our galaxy, just scattered further away from the main disc. Looking with binoculars or a telescope though will reveal truly deep space and the presence of objects hundreds of thousands or millions of light years away!

Starting to the northeast, look off the triangle of the constellation of Cassiopeia for the galaxy M31, The Andromeda Galaxy. The closest major galaxy to our own, M31 is a mere 2.5 million light-years away. If you can’t find it with binoculars, don’t worry, it’s getting closer to us! At a velocity of about 68 miles per second, it will be huge in our sky as it collides with the Milky Way in a short five billion years.

If you don’t have time to wait, look a little down toward the eastern horizon from M31 for M33, the Triangulum Galaxy. At around 2.73 million light-years away, it’s a great deal smaller, about a quarter of the diameter of the either M31 or the Milky Way. It’s still bright in the sky and home to about 40 billion stars, making it a pretty typical spiral galaxy. If you’re observing under very dark skies, you might even be able to see M33 with the unaided eye!

The last on the list tonight is much closer to home, and almost directly south. Coming off the head of the constellation of Pegasus is M15, the Pegasus Globular Cluster; look for it about three finger-widths from the Enif. This bright cotton ball of stars contains over 100,000 stars and is in close orbit around the Milky Way, just 33,000 light-years away. It’s also one of the oldest globular clusters astronomers have found, at an estimated 12 billion years old!

Moon Phases

October 1—Full Moon

The Moon is located on the opposite side of the Earth as the Sun and the side we see is fully illuminated.

October 9—Third Quarter Moon

This phase occurs when the Moon is three-quarters of the way through its orbit around the Earth.

October 16—New Moon

The Moon is located on the same side of the Earth as the Sun and is not visible in the night sky. This is the best time of the month to observe faint objects like galaxies and star clusters because there is no moonlight to interfere.

October 23—First Quarter Moon

The Moon is one quarter of its way through its orbit around the Earth, which makes half the Moon illuminated and half dark from our perspective. This is the best time of the month to see the Moon’s surface features like craters and mountains through binoculars or a telescope.

October 31—Full Moon

The Moon is located on the opposite side of the Earth as the Sun and the side we see is fully illuminated.

Deep Sky Objects

October 2 & 29

Blue Moon and the Red Planet
This month we get to observe a Blue Moon—two full Moons in one calendar month. Just before each full Moon, Mars will be visible as a red dot just above the Moon.

October 21, 22

Orionids Meteor Shower from Halley’s comet
We won’t see Halley’s comet again until 2061, but the gas and dust that has come off of the comet can be seen flashing through our sky every year as the Orionids meteor shower. The Orionids are visible during the last week in October, and their activity peaks the night of October 21.