Tuesday, April 7, 2009

The Ellensburg Sky for the week of 4/11/09

Saturday: You know Metis and Thebe and Adrastea and Amalthea. Io and Ganymede and Callisto and Europa. But do you recall? There are 63 Jovian moons in all. Less than 50 years ago, Jupiter was thought to have only 12 moons. But, astronomers are red-nosed with delight that the advent of supersensitive electronic cameras has caused the number of discovered moons to rapidly increase. Jupiter’s 63 moons range in size from Ganymede, with a diameter of 5,262 kilometers, to S/2002 J12 and S/2003 J9, with a diameter of only one kilometer. Our moon has a diameter of 3,475 kilometers. (One kilometer is 0.62 miles.) Saturn is second place in the moon race with 61 (up from 60 last year at this time). Uranus is next with 27. Then comes Neptune with 13, Mars with 2, and Earth with 1. Even dwarf planets have moons. Pluto has 3, Eris has 1, and Haumea has 2. Eris is an outer solar system object that was discovered in 2005 and named in September of 2006. Because it is larger than Pluto, people called it the tenth planet for a while. Haumea, the newest dwarf planet, was discovered in 2004 and officially named a dwarf planet on September 17, 2008. Saturn, the planet with the greatest increase in known moons over the past year, is four fists held upright and at arm’s length above the southeast horizon at 9 p.m. Go to http://www.skyandtelescope.com/observing/objects/planets/A_Guide_to_Planetary_Satellites.html for more information about moons.

Sunday: Today is Easter. How did I know? I looked at my calendar. According to my calendar, this Sunday is the first Sunday after the first full moon after the Vernal Equinox. With rare exceptions, this is how the date for Easter is set on any given year.

Monday: Antares is less than one pinky width to the upper left of the Moon at 5 a.m.

Tuesday: Start saying “Good bye” to the brightest star in the nighttime sky. Sirius, in the constellation Canis Major, is one and a half fists above the southwest horizon at 9 p.m.

Wednesday: Jupiter is one fist above the southeast horizon at 5:30 a.m.

Thursday: Remember the old saying: April showers bring… meteors. The Lyrid meteor shower is typically active from tonight to April 27. The meteors appear to come from a point to the right of the bright bluish star Vega in the constellation Lyra the lyre. This point is about three fists above the east-northeast horizon at midnight tonight and close to straight over head near dawn. The best time to look is just before dawn since that is when the radiant, or point from which the meteors appear to come, is high in the sky. As your Mother might say, dress warm and sit in a comfortable chair for maximum enjoyment. Meteors are tiny rocks that hit the Earth and burn up in the atmosphere. This is typically one of the least interesting major meteor showers of the year with about 10-20 meteors per hour. However, it is also one of the most unpredictable. As recently as 1982, there were 90 meteors visible during a single hour. In addition, the Lyrid meteor shower has historical interest because it was one of the first ones observed. Chinese records say “stars fell like rain” in the shower of 687 B.C.

Friday: This morning’s last quarter moon is in the constellation Sagittarius the archer.

The positional information in this column about stars and planets is typically accurate for the entire week.

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