First, let’s look at what’s happening early in the evening... More than six months have passed since the last opposition of Mars, and the Red Planet is now quite far from Earth: It appears minuscule through a telescope, and its appearance in the sky has dimmed considerably. Mars is now moving rapidly eastward among the stars, but its circumstances make it seem to be standing still, like a runner on a treadmill. This fall, it remains in essentially the same place, low on the southwest horizon in the twilight. Behind it, however, the constellations continue to pass by: In October, Mars moves from Libra into Scorpius, and approaches its rival, the star Antares.
Rival? Antares is the same colour and brightness as the Red Planet: In fact, in the Roman pantheon Mars represented the god of war, which the ancient Greeks named Ares. Antares was therefore “anti-Ares,” the rival of the fearsome Greek god. From October 18 to 22, the gap between Mars and Antares will be less than 4 degrees — the ideal time to compare the two objects side by side. Their colour, though the same, has a very different origin. The Martian surface is covered in a fine dust, rich in iron oxide — in other words, rust. Antares, on the other hand, is a supergiant star located 600 light-years from Earth: The temperature of its distended atmosphere is such that Antares emits light, mostly in the reddish-orange part of the visible spectrum, like a hot element on a stove.
In passing, look for the crescent Moon to appear above Mars and Antares on October 18, about 45 minutes after sunset: a splendid sight against the background colours of twilight.
In the middle of the night
A few hours after Mars sets in the southwest, the brilliant planet Jupiter finally emerges above the east-northeast horizon. It first appears around 10 P.M. at the beginning of the month, and progressively earlier as the weeks pass; by the end of October, Jupiter rises at 8 P.M. Later in the evening, toward midnight, the giant planet gains altitude and becomes an interesting target for telescopes: Its parallel cloud bands reveal themselves, and its four largest moons can be seen changing position in just a few hours. Jupiter culminates high in the south before dawn.
With the naked eye or binoculars, notice how Jupiter gradually approaches the Hyades and Pleiades from week to week — these are the two famous star clusters in Taurus: By January of next year, the giant planet will appear between them. The gibbous Moon will be near Jupiter on the nights of October 4 to 5, and October 5 to 6.
In the morning sky
Early in the morning, three hours before sunrise, its Venus’s turn to appear above the eastern horizon. On the morning of October 3, the dazzling planet passes less than 10 arc minutes (one third the apparent diameter of the Moon) below Regulus, the brightest star in Leo. Over the following days, notice the rate at which Venus moves away from the star. Then, on October 12, its Venus’s turn to receive a visit... from the crescent Moon.
The Orionid meteor shower reaches its peak on the night of October 20 to 21. But with a maximum of only 10 meteors an hour, under dark skies, this shower is somewhat obscure, especially when compared to the famous Perseids of August. The interesting thing about the Orionids is: The interplanetary dust particles that cause these meteors come from the wake of Halley’s comet — the most celebrated comet of all. The shower’s radiant (situated in the constellation of Orion) reaches its optimum height during the second half of the night, a bit before dawn. This augurs well, since this year the crescent Moon will set around 10:30 P.M. — well before the shower’s peak — leaving a dark sky in which to observe the meteors.