It’s time to rise up! It’s time for opposition!
I mean, in our skies, of course – more about opposition, below, but first, here’s the lineup card for July:
The size listed in the right-hand column is in arc seconds (our moon is 1800 arc seconds wide).
||West, upper left of where the sun set. Sets 10pm
|17 arc seconds wide (“), waning gibbous
||Due south at end of twilight, up all evening.
(Brighter than any star)
||Rises before sunset, up all night.
(Brighter than most stars)
|18”, not counting rings
||Rises just after sunset, low in the southeast
(Even brighter than Jupiter! Reddish?)
||Low in the west in evening twilight. Lower right of Venus. Use binoculars first to find.
||+0.5, getting dimmer
(Hard to pick out in the twilight)
| 8” and looking half-lit. Greatest elongation on the 11th.
Yes, Mercury is the ‘first’ planet of the night, then Venus to its upper left, then make a left turn and there will be Jupiter.
As far as opposition is concerned, it’s when an outer planet is opposite of the sun in our sky. It’s also when we are closest to an outer planet. We make a close pass at Mars at month’s end, which follows the oppositions of Jupiter in early May and Saturn at the end of June. With Venus and Mercury findable in the west after sunset, July is not only a month of opposition but a full house, a planetary straight, or five-of-a-kind, as we can see the five classical planets in one night. Okay, this was also true in June.
Some friends in Elmsford saw four of the five with me on June 25th. I wasn’t up for being up at Mars’ rising at 11pm EDT, so we didn’t complete the royal flush.
These are in order from west to east, right to left in the northern hemisphere, except for Mercury, which we can’t see until the sky gets darker, so we have to come back for Mercury. While you are using the bincoulars on Merucry, can you see the Beehive Cluster next to it on the 4th? A thin moon makes a close pass on the 14th.
One more opposition! We come to opposition with magnitude +15 Pluto on the 12th, just southeast of Sagittarius’ teaspoon. It’s right next to a magnitude +5.5 star, 50 Sagittarii that night. The New Horizons spacecraft, on its way to a Kuiper Belt object they’ve nicknamed “Ultima Thule” is in the teaspoon, beyond our sight.
It’s possible to see all five classical planets at once, in mid-July, but Mars will be just rising and Mercury just setting, as shown below.
The color of Mars, as seen by the unaided eye, may vary from orange to salmon to pale pink as the dust storm intensity changes. Mars’ south polar cap is rapidly shrinking as southern hemisphere summer approaches, but clouds over the polar cap may make it look larger. This is the best time for small scopes as the remaining polar cloud hood has high contrast with the orange-yellow dust storm covering the much of Mars now. The storm may leave behind enough dust to make much of Mars salmon-hued until local winds blow away the accumulated dust and the gray areas appear again.
Mars is closest to the sun in September 2018 and earth’s aphelion is on July 5th, so that makes the two planets closer than usual at this opposition. There will be a similar circumstance at the October 2020 opposition, with Mars’ perihelion in our month of August, but earth being closer to the sun and a bit further from Mars. After that, Mars’ oppositions with earth will be when it is nearer to its aphelion and earth’s perihelion and we won’t get as close. The September perihelion also causes Mars to be closest to earth on July 30th, when opposition is on the 27th.
Jupiter’s Great Red Spot is back to being two out of three. It’s a spot looking like a red bump on the southern equatorial belt, but still noticeably smaller than in previous centuries and redder (through my telescope) than earlier this century.
Saturn stays bigger and brighter in July, taking the breath away of observers with a 30-power or more scope. The rings continue to tilt well toward earth, giving the planet a hat-like appearance. A plus 10th magnitude star will pass behind Saturn from midnight to 3am on the 4th-5th. Saturn appears so much brighter than the star, it will be hard to see except in telescopes of perhaps 8-inches or more.
Venus gets brighter, even as we start to notice its thinning phase in binoculars or a telescope. By the end of July, Venus will be still a bit more than half-lit but decreasing. It will also be lower in the sky, despite not reaching greatest elongation until August. Its phase is easier to see in daytime or bright twilight. Regulus tries to hide in Venus’ brightness on the 9th and the crescent moon gets close for a great photo-op with Venus on the 15th.
We don’t get to see the partial solar eclipse over the waters between Australia and Antarctica on the 13th. Neither do we see the deep total lunar eclipse most of the rest of the world sees on the 27th.
We do get to experience larger-than-normal tides around and after the new moon on the 12th-13th. Lunar perigee is five hours after new moon. The full moon on the 27th will be a ‘mini-moon’ as it is the furthest away of any full moon of this year.
The International Space Station is visible from our area after midnight through the 22nd. Visible overflights in the evening start around the 18th. From the 18th-19th through the 21st-22nd the ISS makes five visible passes a night. For some of these passes, the ISS is almost as bright as Venus.
Sunspots are a rarity as the sun continues toward solar minimum.