Champaign-Urbana Astronomical Society
We have not one, not two, not three, but four oppositions this month! Recall how “opposition” occurs when an outer planet is opposite the Sun. Thus the planet is closest to us and brightest in our sky. Being opposite the Sun, the planet rises at sunset and is visible all night. We start with Jupiter which reaches opposition on the 14th. Really anytime this month would be a great time to check out Jupiter. The disk of Jupiter is 47.6” across and it’s a blistering -2.8 in magnitude. Look for Jupiter to the left of the Teapot of Sagittarius (or better yet, use Jupiter to find the Teapot).
Two days later, Pluto reaches opposition. Now even at opposition Pluto is still magnitude 14.3 and requires a pretty good telescope in order to see it, but it’s located below Jupiter in our summer sky. If you want to take a stab at it, Sky & Telescope has put a finder chart in their July issue (p.48). Given it’s near the Milky Way (and a bunch of stars), your best bet is to carefully draw the field of view and then check back in a couple of months to see if you can detect any movement.
On the 20th, Saturn has opposition, just six days after Jupiter. Saturn is also large, appearing 18.5” in angular diameter, but the rings go out to 42.” At magnitude +0.2, it’s fainter than Jupiter and about 7 degrees to the lower left of it. The rings are tilted at about 22 degrees. Get out that telescope and check out the rings! To identify the Moons, see https://is.gd/SaturnMoons. On July 5th, a nearly full Moon makes a nice triangle with Jupiter and Saturn.
The last opposition is the asteroid Pallas, which reaches magnitude 9.6 on July 12th. Pallas was the second asteroid discovered back in 1802 and the third largest at just over 300 miles in diameter. You can find Pallas in Vulpecula, near the summer triangle. Probably the best way to locate it is to find the star cluster Collinder 399 right smack-dab in the middle of the summer triangle. It appears like an upsidedown coathanger.
Mars follows our bright planets by three hours, rising at midnight in mid-July. Mars also brightens from magnitude -0.5 to -1.1 this month and it appears larger, from 11.4” to 14.5”. Though opposition for Mars is months away, you may start to see some surface features if you wait until close to dawn when it’s higher in the sky. Mars starts the month in Pisces but then clips the corner of Cetus before going back into Pisces. On the evening of the 11th, the Moon is just to the right of Mars.
While still in the evening sky, look in the “Oddz & Endz” section for news of Comet Lemmon. In the morning sky, we have Venus re-emerging in the morning sky in the constellation Taurus. At magnitude -4.7, it’s pretty darn bright! This month it goes from rising 2 hours before the Sun to 3 ¼ hours. Look due east roughly 45 minutes before sunrise. On the morning of the 11th, Venus appears to just miss (less than a degree) the star Aldebaran, and the crescent Moon joins the duo on the morning of the 17th. Two days later, the Moon is lower and just left of the planet Mercury. Greatest separation from the Sun for Mercury occurs on the 22nd. This is arguably the best morning view of Mercury of the year.
You might see a few Delta Aquarid meteors near the end of the month (morning of July 30). The Moon will allow for a pretty dark sky after midnight. The Earth is farthest from the Sun on th 4th of July at a distance of 94, 507,635 miles.