Saturday: “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 over the next two weeks. 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. (The earliest sunrise happened last week.) This phenomenon relates to the angle of the Sun’s path near rising and setting. In Ellensburg, that angle is about 66 degrees 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 asymmetry in orbital angles leads to the asymmetry in rise and set times. By the way, the “can’t sleep because it is too light out” line may just be an excuse because the sunset times change by only a few seconds each day this time of year. The sun sets between 9:01 and 9:02 p.m. between June 21 and July 3 2011.
Sunday: Summer is nearly here. How do I know? Because my kids are home from school. Also, because the Summer Triangle is fairly high in the eastern sky at 10 p.m. Vega, the third brightest star visible from Ellensburg, is about five fists held upright and at arm’s length above the east horizon. Deneb, at the tail of Cygnus the swan is about three and a half fists above the northeast horizon. The third star in the triangle, Altair, in Aquila the eagle is two fists above the east horizon.
If you want to put somebody off, tell her or him to wait until Deneb sets. At Ellensburg’s latitude of 47 degrees, Deneb is a circumpolar star meaning it never goes below the horizon.
Monday: Saturn is three fists above the southwest horizon at 10 p.m.
Tuesday: Today is the first day of summer, the day that 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 10:17 a.m.
Wednesday: Jupiter is two fists above the east horizon and Mars is one fist above the east-northeast horizon at 4:30 a.m.
Thursday: This morning’s last quarter Moon is in the constellation Pisces the fish.
Friday: The early summer days are long so take some time to safely observe the Sun. The best way to do that is to go to http://sdo.gsfc.nasa.gov/ and watch the great images and videos that come from the Solar Dynamics Observer, or SDO for short. We are approaching a sunspot maximum scheduled to peak 2013. So what, you say? Sunspots and associated phenomena greatly influence the strength of solar flares. The strongest flares can affect satellites orbiting the Earth and even electronics on the Earth’s surface.
The positional information in this column about stars and planets is typically accurate for the entire week.
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