AstroCal – July 2025

AstroCal – July 2025

 

     On the morning of July 1, 2025, Venus will be shining brightly in the eastern sky in the hour before sunrise.  Shining at magnitude -4-4, it will not be hard to find.  On July 4, the much dimmer object just 2.4 degrees above Venus will be Uranus.  Jupiter (mag -1.9) will emerge from behind the Sun at mid-month where it will be found to the lower left of Venus in the constellation of Gemini, the Twins.  These two bright planets will continue to move closer to each other until they are in conjunction in August.

     Saturn (mag +1.1) will be stationary in the constellation of Pisces, the Fish on July 14.  After that date, the Ringed Planet begins retrograde motion where it will appear to be moving backwards against the star field.  This is an illusion caused when the Earth, in its inner orbit closer to the Sun, passes Saturn which orbits much farther away from the inner Solar System.  Saturn will continue in retrograde motion for the next four and a half months.  Saturn’s rings are tilted 3.5 degrees from edge on and this angle will decrease to 0.4 minutes by November 2025.  Neptune will be 1 degree north of Saturn on July 6 but it will require a small telescope to see. 

     In the evening sky, Mercury will reach its greatest elongation at 26 degrees east of the Sun on July 4 before it fades from view at mid-month.  Mars will move from Leo, the Lion into Virgo, the Virgin.  Look for it in the western sky in the hour after sunset – its magnitude will be +1.5.  The Red Planet will begin the month some 180 million miles from Earth and move farther away to 197 million miles by the end of the month.  The increasing distance will cause its angular size to shrink from 4.8 to 4.4 arcseconds.

     The Moon will be at apogee (251,400 miles from Earth) on July 4 and at perigee (228,700 miles) on July 20.  The waxing phase early in the month will lead to a Full Moon on July 10, followed by the Last Quarter Moon on July17, and the New Moon on July 24.  Look for the Old Crescent Moon in the east just left of Jupiter on the morning of July 23.  The Young Crescent Moon will then appear in the west in the hour after sunset starting on July 25 and 26.  On July 20, the Moon will pass through the stars of the Pleiades Star Cluster in Taurus, the Bull.  The Pleiades cluster is three times the diameter of the Moon so it will fit in the grouping and not completely cover it.

     The ‘broad peak’ of the South Delta Aquarid Meteor Shower will occur on July 29-30.

Our observing challenge for this month is to see how many of the five planets you can see on July 31.  They will span 89 degrees of the sky and in order (from the ENE to the south) will be 

Jupiter, Venus, Uranus, Neptune, and Saturn.  The only planets not visible at this time will be Mercury (which will be at inferior conjunction) and Mars (which will still be too low to the horizon to see).  You can also look forward to seeing a close pairing of Venus and Jupiter next month on August 12 (just 0.9 degrees apart) and the re-emergence of Mercury to their lower left.

     Our historical astronomical event for this month is July 4th which marks the 157th birthday of Henrietta Swan Leavitt.  Born in Lancaster, Massachusetts in1868, she was educated in Cambridge and later enrolled in Oberlin College after her family moved to Ohio.  She later attended the Harvard-affiliated Society for the  Collegiate Instruction of Women which would later become Radcliffe College.  It was at the Society that an astronomy course got her interested in the discipline.  Edward Pickering invited Leavitt to join the permanent staff of the Harvard College Observatory in 1902.  The 80 women Pickering hired to do calculations and data analysis (they were called ‘computers’and included another soon to be famous astronomer, Annie Jump Cannon) were paid $0.25 per hour for their work.

     Leavitt’s field of expertise led her to discover 1,777 variable stars in the Magellanic Clouds.  Her work would be instrumental to Harlow Shapely’s argument that the Sun lies in the outskirts, and not in the center, of the Milky Way Galaxy.  Her discoveries also allowed Edwin Hubble to declare with certainty that our galaxy was not the only one in the universe.  I shudder to think that today, there is a movement to deny Harvard University’s pioneering inclusion of scholars of every background.  Had Henrietta Swan Leavitt been working for the military, would her legacy of achievements now be erased as if they never happened?  Happy 157th birthday, Miss Leavitt.

(Information about Henrietta Swam Leavitt provided by Teresa Wilson of the United States Naval Observatory and originally appeared in the AAS Historical Astronomy Division’s publication in July of 2018.  Wilson is a graduate of Michigan Technological University).

     Compiled by Ken Raisanen of WOAS-FM 91.5 – 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/.  Yearly subscriptions cost $12 and can be started anytime. Comments and questions can be emailed to kraisanen@oasd.k12.mi.us

Top Piece Video:  Okay, so VENUS seems to be a ‘go-to’ astronomy video – Shocking Blue was formed in the late 1960s and this clip showed they were still performing in 19998.