July marks the last month of evening visibility of two bright planets.
They are: Mars, which was so bright between Thanksgiving and Christmas of 2022 and has dropped dramatically in brightness since then; and Venus, which has graced our evening sky since late autumn. Both are currently visible low near the western horizon about an hour after sunset.
We all know that after a big stage show has wrapped up, the actors come out for their final bow. Well, in a sense, we are nearing the end of a celestial show that has been going on for many months and the two main characters will soon be out to take their final bows.
And as a bonus, located in close proximity to these two planets this month is the bright first-magnitude star Regulus in the constellation Leo, the Lion.
Related: Night sky, July 2023: what you can see tonight [maps]
Dramatic end of the evening show
By far, the brightest of these three is the beautiful Venus, now rapidly approaching the sun. Indeed, it is sinking so fast towards the sunset horizon that towards the end of this month, despite its great brilliance, it too may become considerably harder to see.
During the second weekend in July, Venus sets about two hours after sunset; just at the same time that the evening twilight is coming to an end. But by July 23, this dazzling world will set just an hour after sunset, and by the end of the month, it will set only about 20 minutes after the sun.
This is definitely the month to follow Venus, Earth’s ‘evil twin’, with a telescope! Right now, it’s swinging close to our Earth, overtaking us in the planetary race around the sun. In those moments, Venus is the closest thing to us that any major planet can ever come. It also shows an apparent disk larger than any other solid body in the universe except the moon.
July 7 marks the date of Venus’ “maximum illuminated extent”, the “compromise phase” between when Venus appears full but tiny and when it appears nearly six times larger but is only a thin crescent. The greater amount of illuminated surface combined with a moderately large angular size now makes Venus appear truly dazzling, with a staggering magnitude -4.7; shining 25 times brighter than Sirius, the brightest star in the night sky.
In fact, Venus appears so bright now that it can easily be seen with the naked eye in a deep blue, haze-free afternoon sky, if you know exactly where to look; appears as a tiny white dot against the blue sky.
As July progresses, Venus continues to get closer to Earth as it appears to curve towards the sun in our sky. It now appears as a large beautiful crescent that can be glimpsed even with well-maintained binoculars. On July 7, Venus is 37 million miles (60 million km) from Earth. Its disc appears 25% illuminated and about 35% larger than it did just a month ago.
Your best telescopic views will likely be in early twilight or even during the day when it’s most clearly seen without its overwhelming glare of light. Will you be able to distinguish the extensions of the crescent cusps towards the end of July? These are strands of light that extend beyond the crescent points. Also, examine the cusps themselves; sometimes one appears slightly brighter or sharper than the other.
Mars meets Regulus
While Venus is stepping out in a literal blaze of glory, Mars is sulking in comparison, appearing as nothing more than a nondescript speck. At magnitude +1.7, it is now only 1/27th brighter than last December. On July 7, Mars is about 4 degrees to the upper left of Venus, and over the following nights the two planets will slowly drift apart.
But when Venus and Mars separate, Mars will also come noticeably closer to Regulus. On July 10, Regulus will make close contact with Mars. Seen from 40°N latitude, the pair will set together just after the end of evening twilight.
While you may be able to glimpse both star and planet with your unaided eyes, you’ll really need binoculars to get the best views of this second-magnitude planet that passes just seven-tenths of a degree above the brighter Regulus ( magnitude +1.4). The optical aid will show the striking contrasting colors of bluish-white Regulus and orange-gold Mars, accentuated by the proximity of the objects to each other.
Telescopes, however, will barely reveal Mars’ tiny disk, now only about a fifth as wide as it appeared during the planet’s close approach last December. During August, Mars will be lost in the glare of the sun and remain out of sight for the rest of the year.
The moon has bid farewell
And finally, there’s our closest neighbor in space, the moon, which will be interacting with both planets and also Regulus on the evening of Thursday, July 20. Make sure you get out half an hour after sunset and look down on the western horizon. Look first for the thin crescent moon, only 9% illuminated in the twilight sky; it will be located 8 degrees almost directly above Venus.
This, incidentally, will mark the last gathering of these two brightest night-sky objects visible in the evening skies this year. Regulus, meanwhile, will find himself almost directly between them. And sitting about 4 degrees to the left of the moon will be Mars. Again, binoculars will come in handy to spot them all.
If you’re hoping to catch a glimpse of one of these celestial events in July, our guides to the best telescopes and best binoculars are a great place to start.
And if you’re looking to take photos of the planets or the night sky in general, check out our guide on how to photograph the moon, as well as our best cameras for astrophotography and the best lenses for astrophotography.
Joe Rao serves as an instructor and guest lecturer in New York Hayden Planetarium. He writes about astronomy for Natural History JournalTHE Farmers Almanac and other publications.
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Image Source : www.space.com