Go Stargazing! May Edition

Saturn
Creative Commons License photo credit: Elsie esq.

Saturn is now in the south southeast at dusk.  We are seeing its rings a little more edge on than earlier in the year.  In fact, Saturn’s rings won’t be this edge-on to us for another 15 years.  Saturn, like Earth, is tilted on its axis (at 26.7 degrees, Saturn’s tilt is a little greater than Earth’s).  Twice per Saturn orbit, then, about every 15 years, Saturn has equinoxes where the sun is aligned with Saturn’s equator.  Since the rings orbit the equator, this puts the sun (and the Earth) in Saturn’s ring plane.  Earth was exactly in Saturn’s ring plane on September 3, 2009 when Saturn was also on the far side of the sun and hard for us to see.  This month, Earth again approaches (but will not cross) Saturn’s ring plane.  That’s why the rings appear so thin in telescopes now. Learn more about the rings of Saturn in my latest blog post.

Venus keeps getting higher in the evening sky during May.  Face west at dusk and look for a point of light that outshines everything in the sky but the sun and the moon.

Mars is very high in the evening sky, although not as bright as it was in winter.  Since January 29, Earth has been pulling ahead of Mars on its faster orbit.  As a result, Mars gets slightly dimmer each night for the rest of 2010.  However, during May, Mars remains brighter than average, and thus remains easy to see.  Look high in the west at dusk for a reddish point of light.

Jupiter is low in the southeast at dawn this month.  Look for it low in twilight as day begins to break.  It will be higher in the southeast by the end of the month.

In May, you can watch as the Dog Days begin!  We are in the Dog Days when the Dogs have vanished from the sky.  As May begins, Orion, the Hunter is clearly visible due west right after sunset.  To his left, aligned with Orion’s belt, is Sirius, the Dog Star, the brightest star we see at night.  Forming a triangle with Sirius and Orion’s brightest star Betelgeuse is Procyon, the Little Dog Star.  Throughout May, watch as Sirius appears slightly lower and lower to the horizon each night, until it is gone by May 31.  By mid-June, Procyon is gone as well.  When the Dogs are up only in the day, we’re in the Dog Days.

Meanwhile, spring stars are high in the south and east.  A distinct backwards question mark shape outlines the mane and forepaws of Leo, the Lion.  Three stars forming a right triangle rise underneath; they mark Leo’s hindquarters.  The Big Dipper is as high as it ever gets in the north at dusk. You can extend the curve of its handle to ‘arc to Arcturus’ and then ‘speed on to Spica’.  These stars high in the east and southeast, respectively, by dusk tonight.

星空下的汗腾格里峰 / Mt. Khan Tengri under Galaxy
Creative Commons License photo credit: livepine

As Orion and Sirius set, the plane of the Milky Way largely coincides with the horizon.  (At Houston’s latitude, the two planes are off by less than three degrees).  We are therefore looking straight out of the Milky Way plane when we look up early on a May evening.  Thus May evenings have fewer bright stars, as most of the brightest stars in the Milky Way plane are ringing the horizon.

Moon Phases in May 2010:

Last Quarter                 May 5, 11:15 pm

New                                  May 13, 8:05 am

First Quarter                May 20, 6:43 pm

Full                                    May 27, 6:07 pm

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