Thursday, September 20, 2012
The Ellensburg sky for the week of 9/22/12
Saturday: At precisely 7:47 a.m., 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 6:50 a.m. and sets at 6:58 p.m. Day and night are closest to equal duration on Tuesday.
Sunday: “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.
Monday: Jupiter is one fist above the east-northeast horizon at 11 p.m. By 6 a.m., it is more than six fists above due south. Venus, the brightest point of light in the sky, is nearly three fists above the east horizon at 6 a.m.
Tuesday: Did you time the exact length of the day and night on Saturday, 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 middle part 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 still below the horizon. Day and night are closest in duration today.
Wednesday: It has been dry in Ellensburg. But for a few days each month, the moon often spends time in the watery part of the sky. Tonight is one of those nights. At 10 p.m., Capricornus, the sea goat is one to two fists to the lower right of the moon. Aquarius, the water bearer, is just above and to the right of the moon. Piscis Austrinus, the southern fish, is three fists below the moon. This constellation features the bright star Fomalhaut.
Thursday: The bright bluish star Vega is nearly straight overhead at 8 p.m.
Friday: The cloudy season is coming to Ellensburg. Don’t feel bad. According to astronomers from the European Southern Observatory, it is always cloudy season on HD 85512b, a newly discovered planet orbiting the star called… wait for it… wait for it… called HD 85512. These astronomers developed a method to estimate the cloud cover on planets orbiting distant stars. They think HD 85512b may be cloudy enough to have liquid water on its surface even though it is fairly close to its host star. While the presence of surface water does not guarantee finding life, it is a critical component. For more information, go to http://goo.gl/bGxMD.
The positional information in this column about stars and planets is typically accurate for the entire week.