Western Slope Skies: Pre-Dawn Planet Congregation

Oct 9, 2015

If you rise early on these crisp October mornings, you may see an eye-catching planetary sight in our pre-dawn sky. 

Eastern sky at 6:15 a.m. Saturday, Oct. 10th

Find a spot with an unobstructed eastern horizon.  If skies are clear at about 6 a.m. on October 10, you’ll see brilliant Venus, our nearest planetary neighbor, shining just below and to the right of the star, Regulus.  Below and slightly left of Venus shines the giant planet, Jupiter.  While Jupiter is currently brighter than any star in our sky except Sirius, Venus appears 14 times brighter yet.  If you look closely just above Jupiter, you may see reddish Mars, now shining rather feebly, about 20 times fainter than Jupiter.   If these 3 planets aren’t enough to brighten your morning on October 10th, there’s also a thin crescent moon directly below Jupiter.  By October 15, the planet, Mercury, will join the group, but it will be hard to see, shining low on the eastern horizon in the glare of twilight.  

Venus is nearly the same size as Earth, and it’s now fairly close to us, which explains its brilliance.  Jupiter, while much larger than Venus, is now 10 times more distant, so it’s less bright.  Mars is smaller than Venus, and it’s currently on the opposite side of the sun from Earth, so Mars is now about as faint as it ever appears to us.  Mercury is the smallest planet, orbiting so close to the sun that it’s usually difficult to see.  While these planets now seem to be close together from our perspective, they’re really far apart in space.  On October 10th, distances from the Earth to Venus, Mercury, Mars, and Jupiter are 52, 76, 215, and 572 million miles, respectively.  But the moon is relatively nearby, only 250,000 miles away.  

Between October 10 and 26, Venus, Jupiter, and Mars will appear to converge.  On the morning of October 26, they’ll form a tight triangle that you can almost cover with your thumb when held at arm’s length. While planetary conjunctions occur often, it’s rare when 3 planets form such a tight grouping in our skies!  That’s going to be an amazing sight!  

Western Slope Skies is produced by members of the Black Canyon Astronomical Society.  This episode was written and recorded by Art Trevena.