Bakersfield Night Sky — October 4, 2025
Tickets are available for “Black Holes” showing on October 23 and for the November 6 showing of “Earthquake” at the William M Thomas Planetarium. Links to the ticket sites for the regular Planetarium shows and for Mesmerica are posted on the William M Thomas Planetarium’s Shows page at bakersfieldcollege.edu/community/planetarium/shows .
Tomorrow evening, October 5, will see Saturn and a waxing gibbous moon rising together in the southeast at sunset. Saturn will be bright enough to see it to the lower right of the nearly full moon. Although both of them are in the Pisces constellation, the stars of Pisces are too faint to see from the light-polluted skies of Bakersfield. However, you may be able to see the Great Square part of Pegasus above the moon and Saturn.
High overhead in the early evening will be the Summer Triangle stars of Deneb in Cygnus, Vega in Lyra, and Altair in Aquila. Vega is the brightest of the three stars because it is relatively nearby at 25 light years away and has a large luminosity (total power output)— it is almost twice as hot as the sun and emits about 47 times the sun’s energy. Next brightest is Altair at just 16.7 light years away and a luminosity of about 10.6 times that of the sun. Altair spins so quickly (rotational period under 8 hours) that it is significantly oblate (bulging at the equator). It bulges so much at the equator that there is a large difference in the temperatures at the poles vs. at the equator: about a thousand degrees warmer than the sun at the equator but about three thousand degrees warmer than the sun at the poles.
Deneb is the dimmest one of the three because of its great distance. However, its distance is poorly known. The most accurate way to measure the distance to stars is using the trigonometric parallax method that involves taking a picture of a nearby star from opposite sides of Earth’s or a spacecraft’s orbit around the sun. A nearby star will appear to shift position relative to the background stars due to the parallax; the closer the star is, the greater is the parallactic shift. You can see the parallax effect by looking at your thumb close to your face with just one eye and then with the other eye. As you wink back-and-forth with one and then the other, you’ll see your thumb shift position. When you hold your thumb far from your face, the parallax will be smaller as you wink back-and-forth. If you know the distance between your eyes and measure the angle of the parallactic shift, you can use trigonometry to derive how far your thumb is from your face. Now, of course, a tape measure would be easier to use for your thumb but we don’t have that luxury for measuring star distances. We have to use trig parallax for the nearby stars.
The European Space Agency’s Hipparcos mission in the 1990s measured a parallax distance for Deneb of 2600 light years. However, a reanalysis of Hipparcos’ data with improved techniques and greater computer power showed Deneb to be between 1336 and 1841 light years with a best guess of 1548 light years. That’s a large uncertainty. Unfortunately, ESA’s follow-up mission called Gaia in the late 2010s that measured the distances to about two billion objects in the Milky Way, couldn’t observe Deneb because Deneb is too bright. Bright stars would have saturated Gaia’s sensors, so Gaia stuck to the more numerous fainter stars.
You can use a star’s apparent brightness as viewed from Earth and its distance to derive its total power output (luminosity). Using either the 1548 light year or 2600 light year figure for the distance, Deneb is very luminous: 55,100 to 196,000 times that of the sun and has a temperature about three thousand degrees warmer than the sun. Deneb is a blue supergiant star. It would easily be the brightest star in the night sky if it was as close as Vega or Altair!
The usually weak Draconid meteor shower that produces a few meteors streaking out of the head of Draco, the Dragon, in early October might have a stronger shower this year because its parent comet, 21P/Giacobini-Zinner, making the dust trail we run into, had a close approach to the sun last March. We’ll run into the dust trail on October 8. However, the moon will be less than two days after full phase, so that will dampen the prospects a bit.
One interesting astronomy discovery is the five-image “Einstein Cross” lensing of the very distant galaxy “HerS-3” 11.6 billion light years away. Galaxy clusters warp the spacetime around them, so that any light coming from behind the cluster is deflected. If the alignment is just right, the warped spacetime acts as a lens creating multiple images of a distant galaxy. Usually, just four images are seen but the HerS-3 Einstein Cross has five images because of a trillion solar-mass dark matter clump in the closer galaxy cluster which is “only” 7.8 billion light years away.
The galaxy HerS-3 is a young galaxy forming lots of stars. If a supernova goes off, we’ll see it happen at different times in the five images. The time delay in those displays depends on the expansion rate of the universe, so observing a supernova in HerS-3 could give us a better handle on the value of the Hubble Constant we use in converting the easily observed speeds of distant galaxies to their distances. With the distances, we create the maps of the universe!
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Director of the William M Thomas Planetarium at Bakersfield College
Author of the award-winning website www.astronomynotes.com
