October 2021 Astronomy

October 2021 Astronomy

The summer stars have moved into the Western Hemisphere and are replaced by the less prominent autumn stars in the east

Our attention is usually drawn to shapes of geometrical figures. At mid-month, high in the east is the Great Square of Pegasus, “standing” on its southeast star, Algenib. Extending toward the north from the leftmost star (Alpheratz) is the constellation Andromeda. Above the line of faint stars is the Andromeda Galaxy. This galaxy is best seen from under a dark rural sky, but the light you see was left on its journey toward us 2.5 million years ago, when our remote ancestors were still concentrated in Africa.

Looking toward the north in mid-month, the Milky Way rises vertically from the northeast, up and over your shoulder and down into the southwest. Halfway up in the northeast is the constellation Perseus and a worthy target for binoculars: Around Perseus’ brightest star (Mirfak) is a large cluster of young stars called Melotte 20, some of which is still visible from a city’s suburbs, since this object is composed of stars instead of faint nebulae.


Oct 6 New moon; Aquila (Altair) on meridian at 8 p.m.
Oct 12 First-quarter moon
Oct 18 Saturn on meridian at 8 p.m.
Oct 19 Cygnus (Deneb) on meridian at 8 p.m.
Oct 20 Full Moon
Oct 22 Capricornus, Saturn and Jupiter near meridian at 8 p.m.
Oct 25 Mercury max elongation (18.4 degrees – morn)
Oct 28 Last-quarter moon
Oct 29 Venus max elongation (47 degrees – eve)
Oct 31 Sun enters Libra




When at opposition, planets will appear on the opposite side of the sky from the sun—very roughly on the meridian at midnight.

A conjunction is when the planet has the same “longitude” as the sun. A superior conjunction is when the planet is on the other side of the sun, and an inferior conjunction is when it is between Earth and the sun. Only Mercury and Venus can be at inferior conjunction. Maximum elongation is when Mercury and Venus appear farthest from the sun in our sky. This occurs either in our morning eastern sky (morn) or our western evening sky (eve).

Do not apply the Ottawa Time Corrections to the times in this table.

Prominent Constellations By Seasons


Robert Dick
Robert Dick

One of Canada’s foremost writers and educators on astronomical topics, the Almanac has benefited from Robert’s expertise since its inception. Robert is passionate about reducing light pollution and promoting science literacy. He has been an astronomy instructor for our astronauts and he ensures that our section on sunrise and sunset, stargazing, and celestial events is so detailed and extensive it is almost like its own almanac.

Posted on Friday, October 1st, 2021
Filed under Environment | Nature

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