TUNGSTEN VALLEY - Last month we used Mars’ currently backward (retrograde) motion, in Gemini, to pose the question of why planets sometimes go in reverse across the sky. This month, we interview our in-house astronomer, Dr. Emily Luna, for the answer.

F: If planets always revolve just one way around the sun, why do we see them sometimes moving backwards?

L: It’s an optical effect, caused by the fact that we’re standing on a moving platform, the earth. The drawing shows it for Mars, Jupiter, and Saturn. (It’s a slight variation for Venus and Mercury, but the same principle.)

F: It looks weird. Mars goes forward, then backward, then forward again as we fly along past it, on our earth.

L: It’s hard to wrap your head around. I’ll use a couple of real-world, everyday examples for better explanation.

F: Retrograde motion for things here on earth?

L: I’ll give you two easy instances. The first one is, retrograde motion happens every time you go around a bend on a road, although you’ve probably never noticed it. It’s like this: Riding in your car as you approach a sharp road curve, spot some object on the road’s outside shoulder, like maybe a tree or a road sign.

L: Entering the bend, that thing will begin to move -away- from you, pivoting in the direction of your own motion. As you approach it, it seems to swing from you! For example, if you’re in a right-hand bend, the thing will initially go rightward, as well.

L: As you progress, the object’s motion slows down. Then, at the exact spot on the bend where you are aimed directly at it, its motion will completely cease; it stops moving even though you are still flying along at 60 mph or whatever.

L: Finally, it reverses its original motion and now flies backward as you speed along past its position. In our right-hand bend, the object will drop behind you, to your left.

F: I’ve never noticed any of that.

L: That’s because you, like pretty much everybody else, haven’t bothered to really watch most of the things you see in everyday life. But things on mundane roadside curves replicate, optically, the retrograde motions of the heavens.

F: You promised another example?

L: Nederland’s Carousel of Happiness. Watch off-carousel things go by while you’re riding it. Objects initially go forward, in the carousel’s direction, then they stop, then they fly backward past you, and then finally they stop again and go forward again, as they drop far behind you. This precisely replicates Mars’ (and other planets’) retrograde motions.

L: I have to add, Frank, that for four thousand years, as people uncomprehendingly charted planets going forward, backward, and then forward again, in perfect synchronization with their oppositions from the sun, it should have always been a dead giveaway that our earth was not at the center of the Universe, but rather must have been moving in a circle around the sun. But no, it took until 1609 for Europe’s finest mathematician, Johannes Kepler, to finally nail everything down using Tycho Brahe’s decades-long observations of Mars’ retrograde motions. So much for the supposed giantism of human intelligence!

February Fun Astro-Fact: There are 254 named stars in the sky. Of those, 58 are used for navigation.

In February Skies:

Solar Max is Coming! The sun’s 11-year sunspot cycle peaks in July; it’s ramping up now. The next few months are your best opportunity to watch sunspots. See https://skyandtelescope.org/observing/observing-the-sun/ for safe-viewing instructions.

The sun begins the month in Capricornus, entering Aquarius on February 16. At mid-month, Nederland days and nights are 10.5 and 13.5 hours long, respectively.

The moon’s dates are: First Quarter February 5; Full (Snow Moon) February 12; Last Quarter February 20; New February 28.

February Meteors: None of note.

Best Sky Viewing Nights (Minimal Moon): February 1-5 and 20-28.

Sunset (Mid-Month): Capella is bright-white in the northeast. The Andromeda Galaxy is just west of overhead, with Cassiopeia (a squashed “W”) a bit northward. The Great Square of Pegasus is high in the west above Deneb.

Midnight (Mid-Month): Follow the arcing curve of the Big Dipper’s handle to red Arcturus (“Arc to Arcturus”) and then continue onward to bright-white Spica in the southeast. Leo, with burnt-orangish Regulus, is nearly overhead. The Lion’s front looks like a backward-facing question mark. Procyon is bright in the southwest, with Orion and Sirius setting below it. Cassiopeia is low in the northwest.

Sunrise (Mid-Month): Altair is rising while Scorpius’ Antares (looking like the Scorpion’s angry burnt-red eye) is low at due south. Vega is high in the northeast, with Deneb below it and to the left. The great trapezoid of Corvus is low in the southwest. Leo is low in the west while Capella sets in the northwest.

Mercury in Aquarius, is in the sun.

Venus, in Pisces, is the Evening Star, high in the southwest at sunset.

Mars, high in the sky next to the Gemini Twins Castor and Pollux at sunset, completes its retrograde motion and goes forward on the 25th. It sets at 5 a.m.

Jupiter, in Taurus, is high in the sky at sunset, setting at 2 a.m.

Saturn, in Aquarius, has lost its rings! Well, not exactly. But it is edge-on to us for most of this year, meaning you won’t see its rings as they are only a few miles thick. You will still see its main moon, Titan, through binoculars or a telescope. Very low in the west at sunset, setting at 7 p.m.

Notable Space Missions: NASA launches two notable science missions this month, SPHEREx and PUNCH. SPHEREx will map the entire sky in three dimensions, collecting data on millions of galaxies and stars and searching for signs of life in the Milky Way. PUNCH is a set of four small-sats that will explore the sun’s corona.

Frank Sanders, a spectrum scientist, takes astronomy-related inquiries at backyardastronomy1@gmail.com.