AstroCal – July 2023
The most visible planet in the western sky, Venus, will take a dramatic plunge during the month of July. It will begin July 25 degrees above the horizon and will set 2.3 hours after the Sun on that date. By August 1, Venus will only be 3 degrees above the horizon and will set a mere 19 minutes after sunset. During these 31 days, Venus’ distance from the Sun decreases from 45.6 million miles to 28.6 million miles while the disk as seen from Earth will increase from 34 arcseconds to 54 arcseconds. The fraction of the planet illuminated will be shrinking during the month from 31 percent on July 1 to 5 percent by August 1. According to the Abrams Planetarium web page, “The crescent is large enough to be resolved with common binoculars, for example, of about 8 power. To succeed, find Venus very soon after sunset. If you search for Venus in daytime, take care to avoid pointing your optics at the sun!”
As long as you have your binoculars handy, they can also be used to see a couple of close pairs and trios during the month. A July 4 patriotic display of red Mars 3.5 degrees to the upper left of white Venus and 3.5 degrees lower than blue Regulus in the heart of Leo, the Lion. Venus and Regulus will be within 5 and 3.5 degrees of each other from July 9 to July 25 with the closest approach taking place July 15-16. Mars will appear within this same 5 degree circle on July 9-10. Venus will reach its brightest magnitude (-4.7) on July 7 and though Mars will only be shining at a mag +1.7, it is relatively easy to find just above and to the left of Venus.
The early part of the month will feature a Full Moon (July 3), a Last Quarter Moon (July 9) and a New Moon (July 17). The Young Crescent Moon should be visible low in the western sky on the evenings of July 18-19 about 45 minutes after sunset. Mercury (mag. -1.0) will be very low on the western horizon and left of the young Moon on the 18th and just below the slim crescent on the 19th. As the waxing Moon (when the illuminated portion of the Moon is getting larger) will pass just below Saturn (July 7), Neptune (July 9), just right of Jupiter (July 11) and finally, just to the right of Uranus (July 12). Jupiter and Saturn will be at mag -2.2 and +0.7 so they should be easy to find. The rest +5.5 or dimmer so binoculars may be needed to see them.
July marks a couple of other notable events. July 6 sees the Earth at its farthest point from the Sun called aphelion. This puts us 94.51 million miles or 1.017 a.u. (astronomical units) from our closest celestial neighbor. The best viewing of our more distant neighbors located in the Milky Way Galaxy will be during the span covering July 7-20. Viewing our galactic neighbors will get more difficult near the end of the month with the next Full Moon occuring on August 1.
Our historical astronomical event has before and after dates and doesn’t even take place in July (it never hurts to plan ahead). On September 8, 2016, NASA’s OSIRIS-REx (Origins Spectral Interpretation Resource Identification, Security, Regolith Explorer) spacecraft was launched on a mission to visit asteroid Bennu. This mission was more than just another ‘flyby photo op’ – OSIRIS-REx was going to spend time orbiting the asteroid. After identifying four potential sampling sites (labeled Kingfisher, Nightingale, Osprey, and Sandpiper), the craft performed a ‘bump and run’ encounter with Bennu. The samples collected will be returning to the Earth in the Utah desert on September 24, 2023. I remember giving my eighth grade students a current events assignment about this mission when it was launched seven years ago – their class is already two years past graduation. A more detailed account of the Bennu mission will be forthcoming in a future From the Vaults article published in this space.
Compiled by Ken Raisanen of WOAS-FM – information provided by Abrams Planetarium Sky Calendar, Michigan State University. More information and subscription information can be found on their website at http://abramsplanetarium.org/skycalendar/ or on Twitter at http://twitter.com/AbramsSkyNotes. Yearly subscriptions cost $12 and can be started anytime.
Top Piece Video: As long as we mention Leo, the Lion, here is a pretty good cover of Deep Purple’s MAYBE I’M A LEO . . .