January 1, 2023

Early January one-half hour after sunset looking south

Sunday, January 1, 2023

Happy New Year! On Wednesday, January 4, our home planet will be at its closest distance to the sun—just 91.4 million miles, in contrast to Earth's average distance of 93.0 million miles and its farthest distance of 94.5 million miles in early July. All planets move fastest when they are closest to the sun as described by Kepler's second law of planetary orbits, where a line connecting a planet and sun sweeps out equal areas in equal intervals of time. This is one of the three laws of planetary orbits discovered by Johannes Kepler in the first part of the seventeenth century. About a century later, Isaac Newton explained why orbits behave this way due to the force of gravity which increases at smaller distances between objects.

The length of our seasons is determined by where the sun is in relation to the celestial equator—the projection of Earth's equator onto the sky. The sun's great circle path among the stars throughout the year is tipped with respect to the celestial equator because Earth's rotation axis is tilted by 23.5 degrees with respect to its orbit around the sun. At the beginning of the spring and fall seasons (March 20 and September 22, respectively for 2023), the sun is right on the celestial equator and our summer and winter seasons begin when the sun is at its farthest north or south angular distance from the celestial equator (June 21 and December 21). Because Earth moves fastest in its orbit in January, our season of winter (in the northern hemisphere) is several days shorter than our season of summer. 

Of course, these astronomical definitions of the seasons using the position of the sun with respect to the celestial equator don't have to correspond exactly to what we experience in our regional climate. Bakersfield experiences summer-like temperatures for much longer than the roughly three-month official season length! 

All of the naked eye planets are visible in our evening sky tonight. Shortly after sunset from closest to the sun to farthest on our sky (i.e., from right to left) will be Mercury, Venus, Saturn, Jupiter, and Mars. You'll probably need binoculars to pick out Mercury in the twilight glow, so close to the western horizon. Mercury will be between us and the sun on January 7. You'll have an easier time picking out bright Venus slightly farther up in the western sky. Venus will continue climbing higher up in the evening sky for the next five months. In the other end of the sky in the east, Mars will be the bright orange-red “star” about halfway up in the east among the dimmer stars of Taurus. The waxing gibbous moon will be between Jupiter and Mars. The moon will be full on January 6.

Other noteworthy sky events in 2023 will include an annular-total solar eclipse on April 20 for those in western Australia and New Guinea, two full supermoons (when the full moon is also within 24 hours of being at perigee) on August 1 and 30—the  on August 30 the full moon will also be a “blue moon” and the closest full moon of the year, and an annular solar eclipse visible in the western United States October 14. Note that another definition of the full supermoon is when the full moon's distance is equal to or greater than 0.90 (=90%) of the distance from apogee to perigee. Using that definition, then the July 3 and September 29 full moons can also qualify as supermoons, even though perigee happens almost 1.5 days from the full moon. 

In the first three months of 2023, NASA will send two Commercial Lunar Payload Services (CLPS) landers to the moon. In April and June, Japan and India will send their own lander-rovers to the moon. Russia will follow in July. On September 24, the OSIRIS-ReX capsule returns to Earth after a nearly three-year trip with its large sample from the asteroid Bennu. OSIRIS-ReX collected at least two ounces (60 grams) of dust and pebbles from Bennu. That might seem like a small amount but it is twelve times more than Japan's Hayabusa2 probe brought back from the asteroid Ryugu two years ago and the amounts from Bennu and Ryugu are much more than enough for what's needed to analyze with today's sophisticated instruments. 

In October the delayed Psyche mission will finally launch to explore the metal asteroid Psyche and arrive in 2029. The Psyche asteroid may be the exposed core of an early planetesimal whose rocky mantle and crust were blasted away by numerous violent collisions with other asteroids. 

Sometime in 2023, the European Space Agency's Jupiter Icy Moons Explorer (JUICE) launches for Jupiter. It will go into orbit around Jupiter in 2031 and fly by three of the large moons, Europa, Ganymede, and Callisto. It will later adjust its path to orbit around the largest moon, Ganymede, and spend the rest of its life, exploring Ganymede.

One mission we won't hear from anymore is the Mars InSight lander. InSight spent four years taking the measurements we needed to determine the nature and structure of Mars' interior. InSight's last transmission was December 15. NASA kept trying for the next week to contact InSight before concluding that InSight's batteries had run totally out of energy. Although the data collection is now completed, new discoveries are sure to be made in the next several years to decades from analyses of that huge data trove we now have. 

I hope that you'll be able to find a time and place sometime in 2023 to gaze up in wonder at a dark night sky filled with thousands of stars.

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