End of a loop

Mars becomes stationary on June 30.  It has fallen back, as far as it will go, to the end of that Scorpius-Saturn-Mars array in which it has been a performer for the last several months.

Evening horizon 2016 Jun 30

(Don’t forget “right click – view image” to see these illustrations better.)

It ceases moving retrograde (westward, rightward) against the background of the stars; slowly resumes eastward movement.  This is as good a way as any of marking the end of the planet’s time of glory, which began at the other moment when it hesitated (became stationary), nearly 40 degrees to the left.  That was on April 17, so the prominent time for Mars has been 74 days.

What is really happening is that it has seemed, from April 17 till now, to be moving backward because we on our inside track were overtaking it–

3-D view of Earth overtaking Mars

–so that, in a geocentric framework, it has made a loop inward toward us.

Its behavior in the sky is shown in this detail from Astronomical Calendar 2016.

Mars chart, detail

But look back at the first illustration – what’s that block on the horizon?

Well, it’s a house, or maybe a large first brick.  Back when I had to draw these horizon scenes by hand, I used to add some scenery along the horizon; programming hasn’t allowed that, but I thought of a way to start doing it and may build it up.


5 thoughts on “End of a loop”

  1. According to the Sky & Telescope weekly column (I’m consulting that only because I don’t have the AC2016 with me here at work!), Mars shrinks to 16 arcseconds this week, which means that for almost the entire duration of its 74 day “retrograde operation” (a euphemism employed by contemporary military planners to mean “retreat”), it has been larger than at the last two or three oppositions, even at the moments of closest approach in 2012 or 2014. Hope everyone has gotten a chance to take a look! In the last week and half, Syrtis Major has been well placed for evening observing here in Virginia.

  2. Thanks Guy. For what it’s worth, I prefer an unobstructed ideal horizon along which I can mentally project my local horizontal scenery. Illustrations, usually of idyllic farmland, don’t conform to my hilly urban terrain.

    1. I fantasize features variable for distance, direction, region – nevadas, mosques, tornadoes… Even weather. Probably won’t ever do it.

      1. And all displayed via a virtual-reality headset?

        Virtual reality tangent: A member of my astronomy club made a virtual reality headset displaying the stars in the direction you are looking, but with the virtual distance between the two eyepieces set at one light year. As you moved around you could see which stars are closer to us and which farther away very vividly.

Write a comment