The Ellensburg, WA sky for the week of June 20, 2020

Saturday:  Early this morning, the summer solstice occurs. This is when the Sun reaches its highest declination (the official name for sky latitude) of 23.5 degrees above the celestial equator. The celestial equator is the line that divides the northern sky from the southern sky. In Ellensburg, the Sun is about seven fists held upright and at arm’s length above the south horizon at 1:00 p.m. (noon standard time). Contrary to popular belief, the Sun is never straight overhead in Ellensburg or anywhere else in the 48 contiguous states. The northernmost portion of the world where the Sun can be directly overhead is 23.5 degrees north latitude. In ancient times, the Sun was in the constellation Cancer the crab on the first day of summer. Hence, 23.5 degrees north latitude has the nickname "Tropic of Cancer". Because the Earth wobbles like a spinning top, the Sun's apparent path through the sky changes slightly over time. Now, the Sun is in the constellation Taurus the bull on the first day of summer. However, citing the high cost of revising all of the science books, geographers are not changing the name of 23.5 degrees north latitude to "Tropic of Taurus". The first day of summer is often called the summer solstice. However, astronomers refer to the summer solstice as the point in the sky in which the Sun is at its highest point above the celestial equator. Thus, summer starts when the Sun is at the summer solstice point. This year, that happens at 2:45 a.m. Pacific Daylight Time.

Sunday: Today is Father’s Day, the day to celebrate the person who made you a father. No, not her. You celebrated her last month. (You didn’t forget, did you?!) Celebrate your child by getting her/him the book “Woman in Science” by Rachel Ignotofsky (http://www.readwomeninscience.com/). This creatively drawn book highlights the contributions of 50 pioneers of science from Hypatia to Katherine Johnson, the main character in the recent movie “Hidden Figures”.

Monday: “Mom, I can’t sleep. It is too light out!” A poor excuse you say? Good astronomy skills, I say. The latest sunset of the year happens this week. Surprisingly, the earliest sunrise and the latest sunset do not both happen on the longest day of the year, the day of the summer solstice. The earliest sunrise occurs just before the longest day and the latest sunset occurs just after the longest day. This phenomenon relates to the angle of the Sun’s path near rising and setting. In Ellensburg, that angle is about 66 degrees above the southern horizon at noon near the first day of summer. Because of the Earth’s orbit, which causes the Sun’s apparent motion, the angles are not symmetric. The asymmetries in orbital angles leads to the asymmetry in rise and set times. This year, the sun sets at about 9:01 p.m. between June 21 and June 28 as viewed from Ellensburg, WA. Find sunset data for your location at https://www.timeanddate.com/. 

Tuesday: Mars is four fists held upright and at arm’s length above the southeastern horizon at 4:00 a.m. Venus is about a finger width above the east-northeastern horizon at this time.

Wednesday: The bright star Regulus is less than a fist to the left of the Moon tonight. They are low in the western sky at 11:00 p.m.

Thursday: Jupiter and Saturn are about a half a fist above the southeastern horizon at 11:00 p.m. Jupiter is the brighter of the two planets.

Friday: Don’t wait until next weekend to watch those wimpy firecracker shows. Find the hypergiant star Rho Cassiopeiae. Astronomers think that Rho Cassiopeiae will likely go supernova (explode) in the near future. Of course, for stars, “near future” might mean today. It might mean 20,000 years from now. Rho Cassiopeiae is in the constellation Cassiopeia the queen. At 11:00 tonight, Cassiopeia looks like the letter “W” about three fists held upright and at arm’s length above the northeast horizon. Rho Cassiopeiae is about a finger’s width to the right of the rightmost star in the “W”. Once you find it you’ll be thinking, “Big deal, I can hardly see it.” Although it is barely visible to the naked eye, it is actually very bright. It is the 20^th most luminous star in the sky, a whopping 550,000 times more luminous than the Sun.

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.