Friday, March 13, 2009

The Ellensburg sky for the week of 3/14/09

Saturday: Sirius, the brightest star in the nighttime sky, is two and a half fists held upright and at arm’s length above due south at 8 p.m.

Sunday: Ask someone on which day in March the day becomes longer than the night. Go ahead, ask someone. Why are you still reading this? I can wait. If they said the first or second day of spring, they are wrong. Today, five days before the first day of spring, is the day in which there are more minutes of daylight than night. There are two main reasons for this. First, the atmosphere acts like a lens, bending light from the Sun above the horizon when the Sun is below the horizon. Thus, the Sun appears to rise before it actually rises and it appears to set after is actually sets. Second, spring starts when the center of the Sun passes through the point called the vernal equinox. But, the Sun is not a point. The upper edge of the Sun rises about a minute before the center of the Sun and the lower edge sets a minute after the center of the Sun. Thus, even if we didn’t have an atmosphere that bent the sunlight, daytime on the first day of spring would still be longer than 12 hours.

Monday: Venus is one fist above the west horizon at 8 p.m.

Tuesday: The bright star Antares in the constellation Scorpius is less than a half a fist to the upper right of the Moon at 6 a.m. Certain regions of South America and Africa will see the Moon block, or occult, Antares. Is an occultation such as this a once in a lifetime event? Should you consider spending your retirement saving to gaze at the wonder of a lunar occultation? Hardly. The moon occulted Antares as recently as September of 2008 and January 2009. Antares is just below the ecliptic, the imaginary line in the sky that the Sun follows throughout the year. Since the moon follows that path, as well, it passes near Antares in the sky a few times a year. Oh, and, by the way, sorry to bring up your retirement savings. I know that’s a sore subject now days.

Wednesday: This morning’s last quarter moon is in the constellation Ophiuchus the serpent bearer.

Thursday: Saturn is three and a half fists above the southeast horizon at 10 p.m.

Friday: Look up in the sky. It’s a plane. It’s a bird. No, it’s the vernal equinox. The vernal equinox!? Spring starts at 4:45 a.m. Pacific Daylight Time The first day of spring is often called the vernal equinox. This label for the day is misleading. The vernal equinox is actually the point in the sky where the Sun’s apparent path with respect to the background stars (called the ecliptic) crosses the line that divides the stars into north and south (celestial equator). This point is in the constellation Pisces the fishes. At the vernal equinox, the Sun is moving from the southern region of background stars to the northern region. This marks the beginning of six months of days being longer than nights in the northern hemisphere. Since the Sun crosses the vernal equinox in the evening, tomorrow will be the first full day of spring.
You can’t see the vernal equinox. But you can see Jupiter this morning, less than a half a fist above the southeast horizon at 6:30 a.m.
Because the Earth slowly wobbles like a spinning top, the vernal equinox is slowly moving into the constellation Aquarius. By the year 2597, the vernal equinox will reach the constellation Aquarius and the “Age of Aquarius” will begin. Until then, we’ll be in “the age of Pisces”.

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

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