September 18, 2022

Late September at 10 PM looking East - Southeast

Sunday, September 18, 2022

Next Saturday, September 24, is the Dark Sky Festival at Sequoia and Kings National Parks. There will be events happening during the day starting at 10 AM, including a keynote presentation by Kate Gunderson, a mechanical and aerospace engineer now in training to be an astronaut. At night will be star parties in two locations. The Kern Astronomical Society is hosting the more popular one at the Wuksachi Lodge back parking lot and another group will host a smaller one at the Grant Grove Visitor Center. Both take place from 9 to 11 PM Another star party site at Cedar Grove Roads End was just added to the schedule. It'll be from 10 to 11 pm. New Moon will be on Sunday, so the sky is going to be filled with stars, nebulae, clusters, and galaxies on a very dark sky. See for the schedule.

At 10 PM on the night of the 24th, Saturn will be nearly due south at the tail end of the Capricornus. Jupiter will be dazzling bright in the southeast below the Great Square of Pegasus. Jupiter is just two days shy of being at opposition—directly opposite the sun. This particular opposition will be the closest Jupiter gets to Earth since October 1963. It will be a mere 367 million miles from Earth. Back to the night of the 24th: low in the east the beautiful cluster of the Pleiades will be just becoming visible—a gorgeous sight in a telescope. Also visible will be the double cluster at the head of Perseus. One cluster is much farther away from us than the other but nearly in the same direction, so they appear side-by-side on our sky. Mars won't rise until shortly before 10:40 PM if you had a nice flat horizon but it'll be about 11:15 when it becomes easily visible. 

Before you head out to Sequoia, come to the evening public show at the Planetarium on Thursday, September 22. The William M Thomas Planetarium will show “Destination Mars: The New Frontier” that describes the work being done to make the dream of getting humans to Mars a reality. Two Thursdays later, we'll be showing “Dynamic Earth” on October 6 that describes the various parts of Earth's climate system. Tickets for both shows are still on sale through Vallitix.

September 22 is also the date of the autumnal equinox for this year. That date marks the time when the sun crosses the projection of Earth's equator on the sky—the celestial equator—heading southward toward winter. The day lengths are getting shorter and the sun is taking an ever lower path across the sky. Eventually, that will lead to cooler conditions but there is some lag because land and water don't heat up or cool off instantaneously. 

The oceans move a lot of heat energy, many terawatts of it, around the globe as does our atmosphere. The atmosphere acts as a blanket to hold heat in as well as shield us from the energy from the sun. The Moon and the Earth are at the same distance from the Sun but the Moon has a very large change in temperature from day to night due to the Moon's lack of an atmosphere. The Moon's surface temperature at its equator ranges from about -280 deg F (—173 deg C) at night to +242 deg F (117 deg C) during the day!

On September 26 at 4:14 PM, the Double Asteroid Redirection Test (DART) will collide with the  small asteroid Dimorphos which is orbiting the larger asteroid Didymos. Dimorphos is just 530 feet (160 meters) across while Didymos is 2,560 feet (780 meters) in diameter. Neither asteroid is ever going to hit Earth and the impact of DART into Dimorphos is not going to change that fact. However, the change of Dimorphos' orbit around Didymos will be much easier to measure than if we tried the redirection of a single asteroid's orbit around the sun. All sorts of computer simulations have been done to predict what will happen when DART rams Dimorphos but we need to test the computer models with an actual experiment. DART is the first Planetary Defense test mission and it's a simple test—how well can we nudge an asteroid?

At the end of the month, a waxing crescent moon will be just above the red heart of Scorpius, the supergiant star Antares. Look to the southwest about 45 minutes after sunset to see them. Also at the end of the month on September 29, I will be giving the inaugural talk for the Jack Hernandez Phronesis Award + Lecture. It will be broadcast using BC's livestream.

Nick Strobel
Director of the William M Thomas Planetarium at Bakersfield College
Author of the award-winning website