The next few weeks will be an ideal time to observe Jupiter, which reaches opposition on September 26.
The Sun, the Earth and Jupiter will be lined up, meaning Jupiter is directly opposite the Sun in the sky from our Earthly viewpoint. The giant planet will be visible all night long, rising when the Sun sets and vice versa. Above all, opposition is when a planet comes closest to the Earth, making it appear larger in a telescope than at any other time of the year.
This year, Jupiter is in the constellation Pisces, a region of sky that does not have any particularly bright stars. In other words, you won’t have trouble spotting the dazzling planet above the eastern horizon, where it makes an appearance at nightfall. As night wears on, Jupiter rises in the sky and culminates 44 degrees high in the south around 1 a.m. It then sinks toward the western horizon where it vanishes just before sunrise.
So make time in September to observe Jupiter more closely. Regular binoculars are all you need to distinguish its four largest moons: Io, Europa, Ganymede and Callisto. They take only a few days to orbit the planet, making it easy to see their movement.
However, if you want to observe the outer layers of the giant planet and admire the brown cloud bands that stripe its atmosphere, you’ll need a small telescope. And if your instrument is powerful enough, you may even glimpse the famous Great Red Spot, a storm in the upper atmosphere of Jupiter where wind speeds exceed 400 km/h. This storm was first observed by the astronomer Cassini in the 17th century... and has been raging ever since!
Jupiter is the largest planet in the Solar System, located at a distance of 778 million km from the Sun, which is five times farther than the Earth. Composed primarily of hydrogen and helium gas, Jupiter is 318 times more massive and 11 times bigger than Earth—large enough to contain 1,400 planets the size of ours!
The Voyager space probes flew past Jupiter in the late 1970s, revealing a strange and wonderful world to us. Among other things, we learned that Io’s surface is covered with active volcanoes, a surprising feature for a satellite the size of our Moon. The tremendous tidal forces generated by Jupiter keep Io’s core molten, giving rise to the volcanic activity that we see.
To date, there are 79 natural satellites orbiting Jupiter, most of them only a few kilometres across. We also discovered that the Jovian planet is surrounded by thin rings.
Jupiter and Saturn in the evening sky
Considerably fainter than Jupiter, Saturn is also visible in the September sky, about 40 degrees to the right of the giant planet, in the constellation Capricornus. By mid-September, Saturn appears above the southeastern horizon at dusk and culminates in the south around 11 p.m. On the evening of the 7th, the waxing gibbous Moon will sit about 8 degrees to the right of Saturn, slightly lower in the sky. The next evening, the Moon can be found to its lower left. On the night of September 10 to 11, the waning gibbous Moon will gradually swing less than 5 degrees below Jupiter. The next evening, the Moon will glide to the left of the giant planet.
Mars and the Pleiades
Mars is currently in the constellation Taurus. In early September, the planet rises above the east-northeastern horizon just before midnight and culminates southward at dawn. Mars has earned its “Red Planet” moniker, but be careful not to confuse it with Aldebaran, the alpha star in Taurus that has a similar reddish colour and is located a few degrees away, currently shining less brightly than the planet. Mars will also lie just below the magnificent Pleiades star cluster.
By mid-month, the waning gibbous Moon will visit this part of the sky, drawing closer to Mars and serving as a guide to help you locate it. In the late evening on September 15, Mars will sit to the left of Aldebaran and the Moon will be above it, forming a triangle in the sky. The next evening, the Moon will hang to the immediate left of Mars.
Note that the autumn equinox takes place on September 22 at 9:03 p.m. EDT, marking the start of fall in the Northern Hemisphere: The season will last exactly 89 days, 20 hours and 45 minutes.