Friday, September 21, 2018
The Ellensburg WA sky for the week of 9/22/18
Saturday: At precisely 6:54 p.m. PDT, the center of the Sun crosses the celestial equator and passes into the southern sky. The celestial equator is an imaginary line that divides the sky into a northern and southern half. When the Sun is in the southern half of the sky, it appears to take a shorter path from rising to setting. It also does not get as high in the sky at noon. This leads to shorter days and longer nights. Since the Sun crosses the celestial equator today, there is an instant when it is equally in the northern and southern sky, called the north and south celestial hemispheres. This so-called “equal night” is given by the Latin word equinox. Thus, today is known as the Autumnal Equinox. However, the day and night are not of equal duration today. The sun rises at 6:49 a.m. and sets at 6:59 p.m. in the northern latitudes of the United States. Day and night are closest to equal duration on Tuesday.
Sunday: Venus is at its brightest this week. But that doesn’t mean it is easy to see because it is very close to the horizon right after sunset. Try to spot it right above the southwest horizon right after sunset. Jupiter is a little bit higher, about a fist held upright and at arms length above due southwest at 7:15 p.m.
Monday: Shine on, shine on harvest moon, up in the sky. It’s just like a full moon in January, February, June and July. The only difference is that near the Autumnal Equinox (also known as the first day of fall), the full moon rises close to sunset resulting in a full night of light for the harvest. The harvest moon looks more orange than usual when it is near the horizon because of the dust kicked up from the harvest. The dust scatters the white light reflecting off of the Moon resulting in slightly more of the red and orange components of the white light reaching your eyes. Although the Moon has a dull yellow color whenever it is near the horizon owing to light scattering off of dust and atmospheric particles, the effect is more noticeable for the harvest Moon. For more information about the harvest moon, go to http://earthsky.org/space/harvest-moon-2
Tuesday: Stuart Sutcliffe was the fifth Beatle. d’Artagnan was the fourth Musketeer. Ophiuchus is the thirteenth constellation in the Zodiac. The Zodiac consists of all the constellations that the Sun appears to line up with as the Earth’s celestial perspective changes throughout its annual orbit. You know twelve constellations in the Zodiac because they are the 12 horoscope signs. But the Sun also lines up with Ophiuchus for about two weeks every year. You can spend some time with Ophiuchus tonight. The center of the coffin shaped group of stars is three fists above due southwest at 8:30 p.m.
Wednesday: Saturn is one and a half fists above the south-southwest horizon at 8:30 p.m.
Thursday: “There’s water in them thar craters”, frozen water, that is. There has been speculation since the 1960s and indirect evidence since the 2000s of water on the Moon. Recently astronomers studied data from the Moon Minerology Mapper, the Lunar Orbiter Laser Altimeter, Lyman-Alpha Mapping Project, and Diviner Lunar Radio Experiment. The light reflecting off the bottom of craters near the lunar South Pole showed characteristics of light reflecting off pure ice in their labs. The water likely came from comet impacts or other solar system objects with trace amounts of water ice. For more information this discovery, see https://goo.gl/P4zvtU.
Friday: Mars is two fists above due south at 9 p.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.