October will be particularly active this year, with many eye-catching elements to look at, namely a “blue” Moon, a meteor shower and a planetary duo. But the focus will undeniably be on Mars.
Mars in opposition
Mars, fourth planet from the Sun, gets its red colour from the iron oxide dust on its surface. Easy to spot, it will be particularly striking this month as it’s in opposition, meaning directly opposite the Sun on the celestial dome. In other words, Earth will be directly between Mars and the Sun. In this alignment, we’re at our closest distance to the Red Planet, which appears at its largest through a telescope. But since planetary orbits are not perfectly concentric, the two phenomena (closest approach and opposition) don’t occur at exactly the same time. This year, Mars will be nearest to Earth on October 6, a mere 62,1 million kilometres (3.5 light-minutes) away. The opposition per se will actually occur one week later, on October 13.
These particularly favourable conditions mean that the Red Planet will temporarily outshine the majestic Jupiter! At our latitude, we’ll also have the chance to see Mars climb more than 50 degrees above the horizon, providing a far better view than during the last opposition in 2018. Mars continues its retrograde motion in the constellation Pisces and will be visible from dusk to dawn every night in October.
The Red Planet and the Moon will also rendez-vous twice during the month. The first of these encounters, on the evening and night of October 2-3, will be quite impressive as the Moon will appear to glide to within just 1 degree below Mars. The two celestial bodies approach each other again on the evening of the 29, but not quite as close this time around.
Let’s start by making this clear: No, the Moon will not turn blue in October. The term “blue moon” in fact refers to the second full moon in a single calendar month. Although less impressive than seeing the Moon actually turn blue, this is still a rare event. This second full moon of October, which occurs on the 31st—that’s right… a full Moon on Halloween!—will also be the smallest of the year, since our satellite will reach the point on its orbit farthest from Earth less than 24 hours earlier. The exact opposite of a supermoon!
Every October, Earth passes through a stream of dust left behind by the famous Halley’s Comet during its various passages around the Sun. When observation conditions are good (free of clouds, moonlight and man-made light pollution), up to 20 meteors per hour can be seen, all appearing to originate from the same point in the sky: the constellation Orion, from which these meteors get their name. This year, the best time to observe the Orionids will be during the night of October 21-22. The crescent Moon will set early, ensuring good viewing conditions for this meteor shower. Don’t forget your wish list!
Mars is not the only visible planet in October. Early risers will have no trouble spotting Venus, which shines like a beacon above the east-southeastern horizon at the end of the night and at dawn. The crescent Moon will hang a few degrees from the Morning Star before sunrise on October 13 and 14.
Two other attention-worthy planets this month are Jupiter and Saturn, which form a striking duo above the southern horizon at nightfall. Saturn (on the left) is the fainter of the pair, but its famous rings are well worth a look through a telescope. Jupiter (on the right) also puts on a beautiful show with its striped atmosphere of light and dark cloud bands.
But Jupiter’s moons are the real show stealers. While the largest planet in the Solar System has more than 60 known moons, four in particular are noteworthy for their size and the ease with which they can be observed using binoculars or a telescope: the famous Galilean moons Io, Europa, Ganymede and Callisto. As the moons periodically pass between the Sun and Jupiter, they cast their shadows on the gas giant, creating a sort of solar eclipse that, through a telescope, looks like a dark patch on the surface of Jupiter’s clouds. On the evening of October 17, we’ll have the chance to observe not one, but two tiny black dots simultaneously crossing the Jovian disc. This double transit will start at 5:26 p.m. and end around 7:30 p.m., and with the Sun setting at about 6 p.m. and twilight coming on shortly thereafter, we’ll have a good hour of telescope viewing in the early evening.