There is nothing particularly astronomical about Halloween which comes each October 31st. Halloween is actually All Hallows Eve, the night before November 1st, which is the Christian feast of All Saints. On All Hallows Eve the faithful remembered the dead. But we can find some astronomical items to mention this October.
October is the peak fall month in the northern hemisphere. Autumn leaves are falling, birds are migrating, and the growing season is slowing. Harvesting, canning, and preserving are more the order of the days. October is also the time of year when we notice sunsets happening earlier and day length dropping rapidly. Though we still hang onto daily savings time until the first weekend in November, we sky-watchers can get out earlier to enjoy the night sky.
Darkness has always been associated with Halloween and this year there will be no Moon in the sky for the “tricks or treaters.” Moon-rise is well past midnight on October 31st. But rising in the east by 9 pm is the famous Pleiades star cluster, which has had a rather sinister reputation throughout history. Seeing the Pleiades on the horizon in late October reminded ancient cultures that winter was getting closer, and that the harvest and storing of food needed to survive whatever kind of winter lay ahead was a top priority.
The Pleiades does not evoke sinister thoughts today for sky-watchers. It is a great open cluster of stars which were presumably formed at about the same time from the same immense cloud of inter-stellar gas. We can count 6 or 7 stars with the unaided eye and binoculars bring in at least 40 stars.
Look south for Mars; 30 degrees up by 8 or 9 pm, among the dim stars of Capricornus; standing out at magnitude –1.3. Though this is far lower than its late August peak of –2.8, Mars is still dazzling. It dims to our sight because we are moving away from it in our faster orbit, and because Mars, at 60% the size of Earth is small, reflecting far less light than say a planet the size of Jupiter. Though it will dim to –0.6 by October 31st, in a telescope, Mars still reveals surface features all month.
Mercury will be in the southwestern sky near the end of the month but very, very low and hard to see. Perhaps the best time to see it will on the 27th, when it lies right below Jupiter. Jupiter at magnitude –1.8, is 10 degrees up in the southwest sky an hour after sunset, but bright enough to spot in the deepening twilight. On October 1st look for Jupiter about 15 degrees to the upper left of Venus.
Despite being at –4.7 magnitude, Venus will be hard to see this month. It will only be 3 degrees above the western horizon 30 minutes after sunset, but if one has a clear view to the horizon, it should be seen. By October 10th Venus will have moved between us and the Sun and will be lost to view until it emerges on the other side of the Sun (right side) early in November.
Finally, Saturn gives us good views of itself in the early evenings. It is found in the south-southwest sky above Sagittarius some 25 degrees up and shining at 0.5 magnitude. Binocular views of Saturn nestled among the rich Milky Way star field of Sagittarius are great, and telescope views of Saturn and its wonderful rings are terrific!