Looking Up column: Riding the planetary race track
Bundle up for colder nights as we head through late fall. Winter’s ahead for us northern hemisphere folk, but the trade-off is longer nights to see more stars, and more bright stars for the evening than any other time of year. Meanwhile, keep an eye on the planets.
Notice how Mars, Saturn and Jupiter, still showing well in the evening sky, are a lot dimmer than they were a couple of months ago. Mars is the reddish one, up high in the southeast after dinner. Look after darkness falls in the southwest for Saturn and Jupiter (which is lower down on the right and brighter).
If you’ve been keeping track of these worlds this year you’ve seen how they have been slipping further west when seen at the same time each night, and dimmer and dimmer. They put on such a good show and we are sorry to see them slip away - but they’ll be back!
What you are really witnessing is the dynamics of the solar system, as the planets move along on their basically concentric orbits around the sun. Worlds closer to the sun move the quickest. As the Earth takes us on a ride (and we’re glad it does), we pass by the outer worlds. They are all circling the sun in the same direction but they can’t keep up with speedy Earth, like horses or race cars on a track.
You’re the jockey and, as you look behind you, the other horses recede from view, getting smaller, and in the case of the planets, dimmer to our eyes.
As we overtake an outer planet, you can observe an even odder motion, known as “retrograde.” At first, we are swiftly catching up and although the outer planet moves west to east like we do, our motion makes it come toward us, east to west. Then as we pass and leave it in our cosmic dust, the outer world appears to make a retrograde loop and resumes going west to east.
You would have to look carefully over several nights and weeks to notice this, taking note of the planet’s location in reference to background stars. The planets are far enough away that this effect isn’t obvious to the casual looker.
Jupiter and Saturn also appear to be getting closer and closer. Keep note of this over the next month. As of the third weekend of November, they are only three and one-quarter degrees apart. (The apparent width of the full moon is only about one-half degree.)
On Dec. 21, Jupiter and Saturn will be astonishingly close, at the moment called conjunction. They will be 0.1 degree apart - one-tenth of a degree or about one-fifth the apparent width of the moon. That’s so close these planets will look almost like they are one and will both fit in a small telescope’s eyepiece at moderate magnification. This is very rare indeed; more later!
Speedy Earth, however, is outmatched by Venus and Mercury, the latter always taking first place trophy because it orbits closest to the sun.
See these two overachievers the next clear morning, about a half-hour before sunrise. Look low in the east-southeast. Venus is higher up and to the right, and is the brighter. The planets will be about 13 degrees apart.
The dawn sky will be fairly bright, so binoculars may help you to see Mercury. As the sky brightens, Mercury and then Venus will be increasingly harder to see.
While the brighter stars are still visible, look to the upper right of Venus for a bright star known as Spica.
Soon, the nearest and brightest star to the Earth - our sun, will break the horizon. See how long you can still catch the brilliant planet Venus with eyes alone; by careful watching, you might still see it after sunrise. Binoculars will help. If you keep it in your view, a small telescope will let you track Venus all day if you want!
How fast do the planets move around the sun? Here’s a handy reference in case someone asks you on the street.
Mercury - 107,083 mph; 87.87 days
Venus - 78,337 mph, 224.7 days
Earth - 66,615 mph, 365.25 days
Mars - 58,853 mph, 686.93 days
Jupiter - 29,236 mph, 11.86 years
Saturn - 21,675 mph, 29.42 years
Uranus - 15,223 mph, 85.75 years
Neptune - 12,146 mph, 163.72 years
Pluto (dwarf planet) - 10,603 mph, 247.92 years.
P.S. the sun - with all its planets - moves around the galaxy at approximately 483,000 mph. It takes about 225-230 million years to go once around the Milky Way!
Hang on to your hats.
Following the moon in its phases and motions are even easier. First-quarter moon is on Sunday, Nov. 22; it’s full on Nov. 30.
Keep looking up at the sky!
Peter Becker is managing editor at The News Eagle in Hawley, Pennsylvania. Notes are welcome at email@example.com. Please mention in what newspaper or website you read this column.