What's up in the Ellensburg, WA sky for the week of June 3, 2023

Saturday: You know Metis and Thebe and Adrastea and Amalthea. Io and Ganymede and Callisto and Europa. But do you recall? There are 95 Jovian moons in all. Just 60 years ago, Jupiter was thought to have only 12 moons. But astronomers are red nosed with delight that the advent of supersensitive electronic cameras has caused the number of discovered moons to rapidly increase. Jupiter’s 79 moons range in size from Ganymede, the largest in the Solar System with a diameter of 5,262 kilometers, to numerous moons with diameters of only one kilometer. Recently, Saturn moved into first in the moon race with the discovery of 62 new moons to bring the total to 146. Uranus is next with 27. Then comes Neptune with 14, Mars with 2, and Earth with 1. Our moon is the fifth largest in the Solar System, with a diameter of 3,475 kilometers. (One kilometer is 0.62 miles.) Even dwarf planets have moons. Pluto has 5, Eris has 1, Haumea has 2, and Makemake has 1. Eris is an outer solar system object that was discovered in 2005 and named in September of 2006. Because astronomers thought it was larger than Pluto, people called it the tenth planet for a while. (More recent measurements show Eris to be a little smaller in diameter than Pluto.) Haumea, the newest dwarf planet with a moon, was discovered in 2004 and officially named a dwarf planet on September 17, 2008. Go to https://solarsystem.nasa.gov/moons/ for more information about Solar System moons.

Sunday: Tonight, Venus is as far away from the Sun in the sky as it will get this orbital cycle. Since Venus is in the evening sky, it is east of the Sun so this occurrence is called the greatest eastern elongation. This evening will be the best evening to observe Venus for the next few weeks. Venus is two fists above the west-northwestern horizon at 10:00 p.m. By early September, Venus will be visible in the morning sky. The stars Pollux and Castor are to the right of Venus. The planet Mars is about a fist to the upper left of Venus.

Monday: Summer is nearly here. How do I know? Because the days are very long. Because the temperature is rising. Because the school year is ending. Also, because the Summer Triangle is fairly high in the eastern sky at 11:00 p.m. Vega, the third brightest star visible from Ellensburg, is about five fists above the east horizon. Deneb, at the tail of Cygnus the swan is about three and a half fists above the east-northeast horizon. The third star in the triangle, Altair in Aquila the eagle, is nearly two fists above the east horizon.

If you want to put somebody off, tell her to wait until Deneb sets. At Ellensburg’s latitude of 47 degrees, Deneb is a circumpolar star meaning it never goes below the horizon.

Tuesday: The questions who, what, where, and when can only be asked with a “W”. At 9:30 p.m., the W-shaped constellation Cassiopeia is nearly two fists above due north. The middle star in the W was used as a navigation reference point during the early space missions. The American astronaut Gus Grissom nicknamed the star Navi, his middle name Ivan spelled backwards. After he died in the Apollo 1 fire, the star name was kept as a memorial.

Wednesday: Antares is one and a half fists above the south-southeastern horizon at 11:30 p.m.

Thursday: The bright star Capella is a half a fist above the north-northwestern horizon at 11:30 p.m. Interestingly enough, it is only about two fists from the Sun. If you viewed Capella from Ketchikan, the southernmost city in Alaska, Capella would be one and a half fists above the horizon. The Sun would be close enough to the horizon that there would be a twilight glow.

Friday: It looks so peaceful up there. But life is not peaceful for Jupiter. According to a recent study by astronomers, Jupiter gets hit by a 5-20 meter diameter asteroid 10 to 65 times a year. For comparison, the object that exploded over the Russian city of Chelyabinsk in 2013 was 20 meters in diameter. Earth gets hit by a 20-meter asteroid about once every 50 years. For more information, go to https://goo.gl/RxPc5G. Jupiter is one fist above the eastern horizon at 4:15 a.m.

The positional information in this column about stars and planets is typically accurate for the entire week. For up-to-date information about the night sky, go to https://nightsky.jpl.nasa.gov/planner.cfm.