APOD: Retrograde Mars (2014 Oct 28)

Comments and questions about the APOD on the main view screen.
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APOD: Retrograde Mars (2014 Oct 28)

Post by APOD Robot » Tue Oct 28, 2014 4:06 am

Image Retrograde Mars

Explanation: Why would Mars appear to move backwards? Most of the time, the apparent motion of Mars in Earth's sky is in one direction, slow but steady in front of the far distant stars. About every two years, however, the Earth passes Mars as they orbit around the Sun. During the most recent such pass starting late last year, Mars as usual, loomed large and bright. Also during this time, Mars appeared to move backwards in the sky, a phenomenon called retrograde motion. Featured here is a series of images digitally stacked so that all of the stars coincide. Here, Mars appears to trace out a narrow loop in the sky. At the center of the loop, Earth passed Mars and the retrograde motion was the highest. Retrograde motion can also be seen for other Solar System planets.

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Re: APOD: Retrograde Mars (2014 Oct 28)

Post by Nitpicker » Tue Oct 28, 2014 4:45 am

Impressive dedication to the job. Nicely presented and annotated, too. And I knew I'd seen those April 3 positions before, in http://apod.nasa.gov/apod/ap140410.html. Good times.

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Re: APOD: Retrograde Mars (2014 Oct 28)

Post by Ann » Tue Oct 28, 2014 5:20 am

Good old Tycho Brahe observed the observed the orbit of Mars with such accuracy back in the sixteenth century that it was possible for Johannes Kepler to use his observations to deduce the laws of planetary motion. Good job, Tycho Brahe and Kepler!

And good job, Tunç Tezel! That's a very fine picture!

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Re: APOD: Retrograde Mars (2014 Oct 28)

Post by Nitpicker » Tue Oct 28, 2014 6:23 am

If you look closely, you can just see the start and end dates of 1580 and 1596, for the Mars observations (including eight retrograde loops) recorded by Brahe, as published in Kepler's Astronomia nova in 1609: http://en.wikipedia.org/wiki/Johannes_K ... nomia_nova

Kepler apparently failed to match the observations with about 40 different oval-shaped orbit models, before finally succeeding with the much simpler elliptical model in 1605. Reading that just now, has made my day!

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Re: APOD: Retrograde Mars (2014 Oct 28)

Post by bovnty-hvnter » Tue Oct 28, 2014 11:13 am

what news of the kepler mission ??

the apod of march 29 2011 entitled kepler suns and planet featured a chart of over 1000 stars and exoplanets detected by the kepler space telescope. while the technology used in the kepler mission is very sensitive the accuracy of the method of exoplanet detection which is relies on chance alignment is questionable. each exoplanet object appearing on the chart requires verification by ground based telescopes as to the correctness of data portrayed in the chart - the relative sizes of exoplanet compared to the parent star.

each exoplanet entry may be the subject of a doctoral thesis in physics complete with raw data from kepler sensors, data interpretation, supporting documentation, artists rendering.

if the kepler mission conclusions are indeed correct, then additional work may be done to build up a complete map for each star system portrayed. this will involve drawing upon multiple scientific principles to interpolate the existence of possible earth-like terrestrial planets which may have been undetected in original imaging results.

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Re: APOD: Retrograde Mars (2014 Oct 28)

Post by bls0326 » Tue Oct 28, 2014 1:02 pm

Thanks Tunc Tezel and APOD. I have heard of and know what the retrograde motion is, but I have never seen an actual plot of the motion. Great plot.

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Re: APOD: Retrograde Mars (2014 Oct 28)

Post by bystander » Tue Oct 28, 2014 1:51 pm

bovnty-hvnter wrote:what news of the kepler mission ??
http://keplerscience.arc.nasa.gov/K2/
Know the quiet place within your heart and touch the rainbow of possibility; be
alive to the gentle breeze of communication, and please stop being such a jerk.
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Re: APOD: Retrograde Mars (2014 Oct 28)

Post by Psnarf » Tue Oct 28, 2014 4:02 pm

It's easy to see how the Earth-centric folks were baffled back in the good old days, when burning Galileo's books seemed like a smart idea.

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Re: APOD: Retrograde Mars (2014 Oct 28)

Post by bystander » Tue Oct 28, 2014 4:16 pm

Know the quiet place within your heart and touch the rainbow of possibility; be
alive to the gentle breeze of communication, and please stop being such a jerk.
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Re: APOD: Retrograde Mars (2014 Oct 28)

Post by Ron-Astro Pharmacist » Tue Oct 28, 2014 8:15 pm

Showing Ceres and Vesta made me think of Dawn.
http://www.nasa.gov/mission_pages/dawn/ ... index.html
Still another date looming in our near astro future? I didn't realize it's "retro" rocket had stumbled momentarily.
http://news.discovery.com/space/asteroi ... 140918.htm
Or is antegrade rocket a more appropriate term? A term at all? Looks like April 2015 is going to be the new date. I'd say we need to keep an "eye on" that date depending on Dawn's docket. My "non-sense" of humor often makes no sense so pardon me and I'll stop. Those at mission control would probably agree - it's time for me to abort. Although I am looking forward to New Horizons.
http://www.spacetoday.org/SolSys/Pluto/ ... izons.html
How convenient that it's powered by plutonium. Did they do that on purpose?
Make Mars not Wars

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Re: APOD: Retrograde Mars (2014 Oct 28)

Post by DavidGovett » Sat Nov 01, 2014 7:26 pm

For this reason, "planet" is Greek for "wanderer."