Bakersfield Night Sky — July 7, 2024
Last Thursday was Earth’s aphelion day, its farthest distance from the sun at 94.51 million miles. Did you feel the difference in the middle of summer? Well, probably not since our temperatures are determined by the angle of sunlight and the length of daylight instead of our distance from the sun. Your calendar might have said that aphelion was on Friday, July 5, instead of July 4. That’s because the precise timing of aphelion was at 10:06 p.m. Pacific Time on July 4 which would be in the morning of July 5 for those in Europe. “Coordinated Universal Time” is the official time used for astronomical events and that is set to the Prime Meridian of 0 degrees longitude—seven hours ahead of us during daylight saving time and eight hours during standard time. (So, when are we going to be done with switching back-and-forth for daylight saving?)
The exact time and date for aphelion does vary by up to two days and the aphelion distance can flex a bit too as well. This is all due to gravitational influence of the planets, especially Jupiter, and the slow precession or wobbling of Earth’s orbit axis. Next year, aphelion will happen on July 3 with a distance of 94.50 million miles and in 2026, aphelion will happen on July 6 also at a distance of 94.50 million miles. In the twenty-first century, the closest approach, perihelion, occurs in the first week of January but back in 1246, the perihelion occurred on the same day as the December solstice. The precession has shifted the perihelion/aphelion dates by about one day every 58 years. By the year 6430, the perihelion will happen on the March equinox.
Tonight you might be able to spot a very thin waxing crescent moon low in the west-northwest. Less than half a fist width at arm’s length below will be Mercury. They will both fit within the same field of view of your binoculars and it will probably take binoculars to see them so close to the horizon. Two days later on July 9, a fatter waxing crescent moon will trail behind Regulus at the end of the sickle part of Leo.
On July 13, the moon will be at first quarter, so it appears half full. It will be right next to the bright star Spica. In fact there is a brief time on July 13 that the moon actually covers up (occults) Spica but for us in Bakersfield, the occultation will start when the sun is still up, so you’ll need to use binoculars to see the moon cover up Spica. Even though it will be in daylight, Spica will be right next to the moon, making it possible to pick out Spica with the skyglow. The occultation begins at 7:37 p.m. on the left (dark) side and ends at 8:53 p.m. on the right (lit) side. Sunset on July 13 will be at 8:09 p.m. with civil twilight ending at 8:41 p.m. Hopefully, our skies will be clear of smoke!
Sometime in the next few months we should see the star system called T Coronae Borealis brighten up in what’s called a “nova”. For those not using binoculars or a telescope, it will appear as a new star in the constellation Corona Borealis. What is happening is that a dying red giant star is dumping gas onto a nearby white dwarf companion star. A white dwarf is an exposed dead core of a former star that is compressed down to the size of the Earth. After years of gas building up on the white dwarf’s surface, the gas layer gets hot and dense enough for nuclear fusion to occur. Unlike the controlled fusion that happens in the cores of stars, this fusion occurs at an explosive rate, blasting the gas outward to form an expanding shell of hot gas. That shell of hot gas produces a lot of light suddenly—a “new star” appears. After the nova burst, the gas begins accumulating again for another burst years later.
In some cases, so much gas accumulates on the white dwarf’s surface to push the total mass of the white dwarf over a threshold called the Chandrasekhar limit of 1.4 times the mass of the sun and the core implodes suddenly, fusing the white dwarf’s carbon and oxygen to make silicon that then undergoes fusion to make nickel with a huge amount of energy released in the process. So much energy is released that the imploding white dwarf blows itself apart to make what is called a Type Ia supernova. These type of supernovae are even brighter than the supernovae that happen when a massive star dies, a Type II supernova.
Novae reoccur while supernovae are one-time MUCH brighter events. T Coronae Borealis’ last nova burst was in 1946 and it has a cyclic period of 80 years on average. Although that means the next burst should happen more like in 2026, T Coronae Borealis is acting like it did just before it burst in 1946, so we’re expecting it to go nova by September of this year. At about 3000 light years away, T Coronae Borealis is among the closest of the nova systems and unlike in 1946, we’ll have an armada of space telescopes and an army of amateur and professional astronomers prepared to discover the secrets of nova bursts. With a period of 80 years, this will be a once-in-a-lifetime event. Come on Blaze Star!
—
Director of the William M Thomas Planetarium at Bakersfield College
Author of the award-winning website www.astronomynotes.com
