There is already enough material in our ancient solar system to invite many generations of people to study all of the objects in it; but recently, objects from far interstellar space have been known to visit us and have found a brief welcome.
In October 2017, an asteroid known as Oumuamua (Hawaiian for “Scout”), or 1I/2017 U1 to give it a dry technical term, was discovered about (33,000,000 km) from Earth (about 85 times as far away as the Moon), and already heading away from the Sun. Oumuamua is a small object, estimated to be between 100 and 1,000 meters long. It flew through the solar system at speeds of greater than 60km per second, making it very difficult to study, and it is not expected to return to the Sun’s vicinity ever again.
Now astronomers have confirmed that a second interstellar object is currently entering the Solar System, and unlike Oumuamua, it will be studied in great detail.
The object is known as C/2019 and is a comet about 10km across with a visible tail, and is about six times brighter and much slower, travelling at 30km per second, giving astronomers about six months or more to study it. It is also expected to get fairly close to Earth on December 10th, reaching 1.8 times the distance of Earth from the Sun, roughly 167 million miles from us.
Mercury passed behind the Sun (Superior Conjunction) on the night of September 04 so will not be visible this month, but will appear during early October in the evening sky right after sundown.
Venus, our nearest planetary neighbor, will set at the end of September in the WSW 30 minutes after sunset, but will be very difficult to see due to the fact it will be at a very low elevation. Binoculars and a low horizon will be needed, but please do not use them until after the Sun has set.
The Moon will next be Full on October 13; this full Moon is known as the Hunter’s Moon as it comes during a traditional month known since antiquity for hunting game at night. It will also come just three days after apogee (furthest distance for Moon from Earth in its eliptical orbit) so is not expected to raise exceptionally high tides as can occur when the Moon is closest to Earth during perigee.
The red planet Mars passed behind the Sun (superior conjunction) on September 02 and thus still lies too close to the Sun to be visible to us. We will have to wait until the end of October to spot it in the pre-dawn sky at the start of its next apparition.
Jupiter is still very prominent in the Southern sky as darkness falls, showing as a bright -2.0 object during the month, As the month progresses, its angular size drops from 39 to 36 arc seconds. Jupiter, in the southern part of constellation Ophiuchus, is now moving away from bright star Antares in Scorpius, initially lying some 7 degrees up and to its left.
Held very steadily in a dark sky, strong binoculars should enable you to see Saturn’s brightest moon, Titan, at magnitude 8.2.
Saturn is now low (at an elevation of roughly 14 degrees) in the south as darkness falls lying above the ‘teapot’ of Sagittarius, east of brighter Jupiter. The ringed planet is a somewhat dim 2.1 magnitude. Held steady, a strong pair of binoculars should enable you to see Saturn’s brightest moon, Titan, at magnitude 8.2.
As Saturn rotates quickly with a day of just 10 and a half hours, its equator bulges slightly and so it appears a little ‘squashed”’ or oblate around the equator. Like Jupiter, it does show horizontal belts but their colours are muted in comparison.
The thing that makes Saturn stand out is, of course, its ring system. The two outermost rings, A and B, are separated by a gap called Cassini’s Division which should be visible in a telescope of 4 or more inches aperture if seeing conditions are good. Lying within the B ring, but far less bright and difficult to spot, is the C or Crepe Ring.