Driftless Dark Skies: Occultation and Conjunction

November 3rd, 2017 by John Heasley

Two special events this month let us experience the Moon and planets moving across the sky.  We are familiar with the daily motion of Sun and Moon and stars and planets rising in the east and setting in the west as our planet rotates about its axis. But we can also see the motion of the Moon as it orbits the Earth and the motion of the planets as they orbit the Sun.

As the spinning of the Earth makes the Moon move from left to right across the sky, its own orbit makes it move from right to left across the stars at 1/30 the speed. This motion is why the Moon rises about 50 minutes later every night. Earth has to rotate a little extra to catch up with the Moon. It takes about an hour for the Moon to move its own width. The movement is so slow that we seldom notice it. But we will on the evening of November 5 when the Moon covers up (occults) the bright star Aldebaran.

Watch for the waning gibbous Moon rising in the ENE around 6:24. Remember that this is the first day of standard time.  Just to the left of the Moon, you will see a bright orange star. That’s Aldebaran. Binoculars may help you to spot it. As Earth’s rotation carries the Moon and Aldebaran higher and to the west, the Moon’s orbit takes it more slowly lower and to the east.  Watch as the Moon gets closer and closer to Aldebaran. Around 7:05 Aldebaran is occulted by the Moon and disappears behind it. Enjoy the sights of the autumn sky, but slew your binoculars back to the Moon by 7:57 to watch Aldebaran emerging from the right side of the Moon around the 2 o’clock position. You’ll notice that the Moon is about 95% full with the right side a bit in shadow. It took the Moon just about an hour to move its own width across the starry sky!

Early risers can see the planets orbiting the Sun as Jupiter and Venus put on their best show of the year. Early in November, look to the ESE around 6am. You’ll spot two bright objects low to the horizon. The brighter and higher of the two is Venus with Jupiter lower and to the left.  Watch as their orbits around the Sun bring them closer together. By November 13, they are side by side in an event called a conjunction. You can easily cover both with just your pinkie. Continue to enjoy the show the rest of the month as Venus’ orbit takes it closer to the Sun and Jupiter’s orbit takes it further away. Don’t miss November 16 when the Moon’s orbit brings it just above the two planets. If you happen to be stargazing on November 22, 2065, you can see an even cooler event when Venus passes directly in front of Jupiter and a conjunction becomes an occultation!

You can join Starsplitters on November 18 at Wyalusing State Park for their club meeting.  Kickapoo Valley Reserve offers Trails by Light of the Frosty Moon on November 4.

John Heasley is an astronomy educator and stargazer who enjoys connecting people with the cosmos. He volunteers with NASA/JPL as a Solar System Ambassador. For more information about stargazing in southwest WI, like Driftless Stargazing LLC on Facebook and find out whenever there’s something awesome happening in the skies. Driftless Dark Skies appears monthly in the Voice of the River Valley.