Saturday, March 19, 2011

March Madness

Greetings, sky-watchers! Please forgive my multi-month absence, but I had the best of reasons. I was moving to a locale with significantly darker skies--an observer's dream come true.

This year, my blogging focus will be on "current events," that is, to inform you of neat celestial events happening in the present or the very near future, as well as to recommend objects for you to look at in your current sky.

It's an eventful time in the sky right now--starting tonight!

1) Just after sunset tonight, look west. As the sunset glow recedes, the first objects you'll see pop out low in the western sky will be two planets. The brighter one is Jupiter. It will be about one fist-width above the horizon. Make a fist and hold it at arm's length against the sky. Measure across the knuckles to approximate a fist-width. About half a fist-width above Jupiter is Mercury, not nearly as bright as Jupiter and pinkish in color. NASA's Messenger spacecraft just this week entered orbit around Mercury--a first in space exploration. We can expect to learn a lot more about this sun-drenched planet in the next year.

You can see the planetary pair for the next few days, after which Jupiter will disappear below the western horizon. Mercury will be do-able for a few more nights, but as we head towards month's end, you'll probably need binoculars to pick Mercury out of the twilight.

2) Tonight about a half hour after sunset, look east to watch the Full Moon rise. This is the "super-perigee moon," the biggest Full Moon in nearly 20 years. It will be in the sky all night, so you'll have plenty of time to gaze upon it.

Why is it so big? The Moon’s orbit around Earth is oval-shaped, with one narrow part of the oval about 30,000 miles closer to Earth. At its closest to Earth, the Moon is said to be at perigee; at its farthest, at apogee. Full Moons that occur near perigee are the biggest and brightest, about 14% bigger and 30% brighter than “apogee moons.” Tonight, the Full Moon occurs a mere one hour from perigee!

Note: the Moon is not closer than it's been in 20 years. I've been hearing this a lot on TV and other media, and hearing people repeating it. The Moon draws close to Earth every perigee, and perigee occurs once every 28 days. It would, however, be correct to say that the Full Moon is closer than it's been in nearly 20 years, because normally the Full Moon does not coincide so closely with perigee.

3) Tomorrow, Sunday, March 20, at 5:21 pm Mountain Time (adjust for your time zone), we celebrate the moment of the Spring Equinox or Vernal Equinox. By convention, this event marks the beginning of the season we call "spring" in the Northern Hemisphere. The Spring Equinox is when the Sun crosses the celestial equator (where the plane of Earth’s equator would intersect the sky), heading north. On the Equinox, the Sun rises due east and sets due west, so you can use this opportunity to mark west and east at your location, using natural or man-made markers on your horizons. (Caution: To protect your eyesight, never look directly at the Sun!)

Until next time, happy star trails to you.