Thursday, September 18, 2014
The Ellensburg sky for the week of 9/20/14
Saturday: “You know Aries and Cancer and Draco and Libra. Leo and Pisces and Virgo and Hydra. But, do you recall, the pointiest asterism of all? Triangulum, the three sided asterism, had a very pointy edge….” Sorry. Some stores have started putting up their Christmas decorations and that has put me in the mood to modify some Christmas songs. Anyway, Triangulum is a small constellation between the more prominent Andromeda and Aries. Its main feature is a skinny triangle oriented parallel to and nearly four fists held upright and at arm’s length above the east horizon at 10 p.m.
Sunday: There is a rumor (started by my dog and me) that The Beach Boys are working on a new solar system-themed record. I bet the first single will be “Catch a Wave and You’re Sitting on Top of Titan.” As the seasons change on this large moon of Saturn, astronomers are looking for signs of the winds increasing. They’ll send the Cassini spacecraft on a flyover of Kraken Mare, a large liquid hydrocarbon sea, to see if there are any waves. The NASA Jet Propulsion Laboratory has made a “Titan Great Lakes” tour video that you can find at http://goo.gl/ndXDhd. Available lakefront property and the potential for large waves. Who is up for a “Surfin' Safari”? Saturn is one fist above the southwest horizon at 7:30 p.m.
Monday: At precisely 7:29 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 6:48 a.m. and sets at 7:02 p.m. Day and night are closest to equal duration on Friday.
Tuesday: To celebrate the start of school at CWU tomorrow, let’s sing a song of the season. “Oh the weather outside is grand. And the fire is rightfully banned. There is really no place to go. Let it snow, let it snow, let it snow. On Mars.” The Mars Reconnaissance Orbiter has discovered evidence of carbon dioxide snow clouds high above the surface of Mars. Carbon dioxide, also called “dry ice”, exists in Mars south polar ice cap and requires temperatures of nearly 200 degrees below zero Fahrenheit to form. Astronomers were not sure how this polar cap gets replenished but the discovery of carbon dioxide clouds may provide an answer. For more information, go to http://goo.gl/shMTf. Mars is one fist above the south-southwest horizon at 7:30 p.m., just to the upper right of Antares, which means “rival to Mars”. Or as Mars calls it, “rival to me”.
Wednesday: Are you ever thirsty at midnight? The Big Dipper is low on the northern horizon at midnight, just waiting to hold water for you.
Thursday: Jupiter is about three fists above the east horizon at 6 a.m.
Friday: Did you time the exact length of the day and night on Monday, the first day of autumn? They were not equal in duration. Many people think that the day and night are the same duration on the autumnal equinox. The day is a little longer than the night for two reasons. First, the Sun is an extended object so even when the lower half has set, the upper half is still above the horizon lighting the sky. The second, and more influential, reason is that the atmosphere acts like a lens, bending light from the Sun above the horizon when the Sun is really below the horizon. Day and night are closest in duration today.
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.