Bakersfield Night Sky — July 5, 2025
Two days ago, July 3, was aphelion day when Earth is farthest from the sun at a whopping 94,502,939 miles away. For us in the northern hemisphere, our part of Earth is tipped towards the sun, so the sunlight angle is much more direct and concentrated and that’s why we have summer in July despite being farther from the sun. The increase in temperature is also helped by the longer amount of time the sun is above our horizon to heat things up. The southern hemisphere is experiencing winter but the greater distance does not make their winters more extreme than ours because of the greater amount of ocean water to land ratio than we have in the northern hemisphere. Water takes a lot longer to cool off (and heat up) than does land.
The 94.5 million miles of aphelion is just slightly more than three percent greater than our closest distance at perihelion (in January) of 91.4 million miles. Earth’s orbit is nearly a perfect circle! The temperature change due to distance alone goes as the square root of the distance or about 1.7% for Earth. Clearly the angle of sunlight has a much bigger effect on our seasonal temperature changes than the distance (and recall that the distance effect goes opposite to what we’d expect for the northern hemisphere since we’re farther from the sun in our summer months).
Mercury is still visible low in the west shortly after sunset. It sets about 90 minutes after sunset but it’s now dropping down closer to the sun, getting fainter as it moves in between us and the sun for inferior conjunction on August 1. Mars is dimmer than Mercury but higher up below the middle of Leo, so Mars will be easier to spot than Mercury. The moon is in the waxing gibbous phase in Libra, getting more fully lit as it heads to full phase on the night of July 9 and 10. The actual full phase happens in the middle of the day of July 10, the amount lit on the evenings of July 9 and 10 will be nearly identical.
Saturn at the western end of Pisces (below the Great Square of Pegasus) becomes visible in the east at about 12:30 a.m. Saturn will be brighter than any of the stars below Pegasus. Super bright Venus becomes visible three hours later at about 3:30 a.m. among the stars of Taurus. At about 5:40 a.m., brilliant Jupiter pops up at the feet of Gemini but that’s just ten minutes before sunrise, so you’ll need to wait until later in the summer to see both Jupiter and Venus in the early pre-dawn sky.
Two new observatories released their first images a couple of weeks ago. NASA’s SPHEREx launched in March to do a near-infrared (i.e., wavelengths just slightly longer than what our eyes can see) survey of the entire sky, getting the color information for 450 million galaxies and more than 100 million stars in our home galaxy, the Milky Way. SPHEREx will determine the conditions for life outside the solar system, understand the history and evolution of galaxy formation, and investigate the earliest epochs of the universe. The first images show that SPHEREx is working very well! The data will be publicly available with images posted to the Infrared Science Archive every week or so for researchers to mine for decades to come.
The Vera C Rubin Observatory’s “First Look” images are spectacular! In just over ten hours, Rubin captured ten millions galaxies and millions of Milky Way stars and over 2000 asteroids with its 3200 megapixel camera and 8.4-meter diameter mirror. Beginning later this year, Rubin will continuously scan the sky every night for 10 years to precisely capture every visible change. It will cover all of the sky visible from its location in Chile every 3 to 4 nights, so we will create an ultra wide, ultra-high-definition time-lapse record of the universe.
With this HUGE database we hope to finally understand the nature of dark matter and dark energy that together account for 95% of the energy determining the overall geometric structure of the universe. Ordinary visible matter (subatomic particles and other particles that interact with light) makes up just 5% of the universe, so being in the dark about the other 95% of the universe is a bit humbling but it also means there is A LOT left to discover about our universe! Rubin’s ability to find millions of unseen asteroids and comets because of its unique ability to quickly find objects that move, is going to be a boon for planetary defense. It’ll be able to identify many more potentially hazardous objects that could impact Earth or the moon in the near future.
The William M Thomas Planetarium is closed for the summer break at Bakersfield College. I hope you’ll be able to enjoy a truly-dark sky filled with stars!
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Director of the William M Thomas Planetarium at Bakersfield College
Author of the award-winning website www.astronomynotes.com
