Mars in retrograde this month

The Sky Guy

Posted: Sunday, November 11, 2007

 

 

Winter has almost arrived and that means that the bounty of the beautiful winter sky charms us once more. The accompanying chart is set for 10 p.m. in late November, thus fewer stars are visible in the east during evening hours earlier in the month (but more in the West); an asterisk denotes stars marked with a letter on the chart.

Orion, Taurus, Auriga and Gemini are visible in the southeast. Inside these constellations are the bright stars of winter: red Betelgeuse* and Aldebaran*, blue Rigel*, yellow Capella* and the twins Castor* and Pollux*; the latter two make a fine triangle with Mars.

Also included is the star cluster of the Pleiades, best viewed with binoculars when up to 50 stars may be seen. Soon the bright stars Procyon and Sirius will follow.

Now near the zenith are Cassiopeia's W, the House of Cepheus, Pegasus' Great Square and the swan Cygnus' Northern Cross.

Always in the same place is the Little Dipper with Polaris*, and atop the northern horizon appears the Big Dipper. The kite-shaped Bootes with red Arcturus is now setting while the summer triangle consisting of Deneb* (the swan's tail), Vega* and Altair* is getting closer to the western horizon.

Mars rises around sunset. Planets move counterclockwise in the Solar System when viewed from North which produces their true west to east motion along the ecliptic and through the Zodiac constellations as seen from one night to the next.

But when the Earth, and we as the observers on Earth, pass a planet, that planet seems to move in the opposite direction: it retrogrades. From November through January it's really easy to see Mars retrograde which is mostly evidence for us passing Mars because there are three stars situated near that are of comparable brightness. In the process of us passing Mars, the red planet becomes also brighter to the naked eye and appreciably larger in a telescope until it reaches opposition on Dec. 19. Observe Mars weekly or even daily; it can be seen to the right (west) of Castor and Pollux in Gemini, moving east-to-west (left-to-right) toward red Aldebaran in Taurus (with the Pleiades further West).

The triangle formed by Castor, Pollux and Mars becomes ever more elongated from mid-November through December until Mars stops retrograding in late January now quite a bit closer to Aldebaran when we have passed the planet enough that we see its true motion again.

Mars is flanked by the almost-full Moon on the 25th (see chart) and 27th of November; on the 26th Mars sits right beneath it.

Jupiter would be visible very low in the southwestern sky during dusk, but only in the southern United States.

Pluto, Neptune and Uranus are too low in the sky as well to be observable from Alaska.

Saturn and Venus are visible during dawn, having developed into a line with Leo's Regulus; from midnight on throughout the rest of the night find Regulus leading Saturn in the east, then around 5 a.m. Venus rises and you can use it to find the now higher-situated star and ringed planet. And since Alaska nights get longer every day, you'll see Venus during your morning commutes, if you're heading east.

Mercury also is visible during early November in the dawn sky. Between 7 and 8 a.m. as you're enjoying dazzling Venus connect an imaginary line diagonally to the lower left from it toward the horizon; you should be able to see Mercury very low on the southeastern horizon. In fact, the similarly bright star Spica is just to the right of it, so look for "headlights" beneath Venus, though Venus is quite a beacon compared to those headlights.

Toward the middle of the month Mercury has moved along, seemingly back toward our sun, now producing a long, slightly curved line with Spica and Venus. Try finding this speedy planet as few people have consciously seen the planet as such.

The Leonid meteor shower peaks in the wee hours of Nov. 18 with an expected average of about 10 meteors per hour.

Comet 17P/Holmes came as a nice fuzz ball into view; it was the 17th periodic comet discovered and recognized as being periodic (1P/Halley was the first) by Edwin Holmes in 1892, with a seven-year orbit that brings it as close as Mars' orbit and as far as Jupiter's orbit. Use binoculars and look halfway between Auriga's pentagon and Cassiopeia's W; the comet is about as bright as the surrounding stars.

Andy Veh is a physics and astronomy instructor at Kenai Peninsula College. He can be reached at aveh@uaa.alaska.edu.



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