Remote moon

Another day another letter… We’re up to R folks and it’s time for a response from my richly-educated, respectful cousin; a re-formulated vegetarian-of-sorts, here known as Renaissance Kid. And he has requested:

Retrograde

Generally retrograde refers to motion that is counter to the normative flow. So you might think of a satellite orbiting earth against the earth’s rotation as retrograde. Most man-made satellites would take an orbit more polar-oriented than equatorial though, so that it’s orbit would compliment the rotation like a sort of x-y axis and would potentially cover most of the planet’s surface over time instead of just a strip.

My understanding is that most are launched somewhat prograde and fewer somewhat retrograde in order to lessen fuel-costly resistance. But sometimes the geography around a launch site will inflict limitations on available direction.

Most satellites would orbit far enough from our atmosphere that resistance and fuel would cease to be of relevance once the orbit is established.

As for natural satellites: Saturn has 82 known moons of unique orbit (not embedded in its primary ring system) of which Phoebe is the only in retrograde (to Saturn’s rotation). It’s a more distant orbit which normally dictates smaller sizes but while a fraction of the size of our own moon it ranks probably in Saturn’s top dozen.

Phoebe, originally designated Saturn IX, was the first ever moon discovered photographically, but only as a dot. The Voyager explorations of the late eighties missed out on a close-up due to her remote position at the time, but this millennium’s Cassini mission was timed with Phoebe in mind. Cassini snapped this photo:

Her orbit and black surface tricked scientists for a long time into believing it a captured asteroid but now we know it possesses some carbon dioxide, and once held heat and water, all of which no proper asteroid can boast, so now we believe it’s a captured “centaur” meaning a Kuiper belt object (from between Jupiter and Neptune)

You may have heard of planets being in retrograde but this is a loose usage of the term. Taking Mercury for example, its orbit is continuous of course but because we sit on relatively the same plane as that orbit, the planet appears to change direction at times in accordance to the complex relationship of our two orbits. When it appears to move opposite the apparent flow of background stars (which is really just our rotation) some folks, such as astrologists, use the word retrograde to describe the unusual juxtaposition.

The last period of Mercury’s apparent retrograde was February 17 to March 10 and the next will be June 18 to July 12, 2020. Astrologers’ advice for these chaotic periods is this:

…remain flexible, allow extra time for travel, and avoid signing contracts. Double check your email responses, check in with reservations before you take that trip.

Review projects and plans at these times, but wait until Mercury is direct again to make any final decisions. You can’t stop your life, but plan ahead, have back-up plans, and be prepared for angrier people and miscommunication. Also, pull your head out of your ass because this is the least defendable baloneypoop ever.

I may have added an extra sentence somewhere in there but you’ll never guess which one.