4 ms·
This is a whole lotta words and graphics to explain something that literally takes two sentences: Phobos orbits Mars faster than Mars rotates itself, while Dei
by mk_stjames 4y ago
This is a whole lotta words and graphics to explain something that literally takes two sentences:
Phobos orbits Mars faster than Mars rotates itself, while Deimos rotates slower than Mars. Thus from the ground their apparent motion is opposing in the sky; Deimos rises in the east and sets in the west, while Phobos does the opposite.
Done.
- ali7388 4y agoThis Earth has many artificial satellites that do that.
- addaon 4y agoThere's not that many satellites outside of GEO, and even those that go beyond are usually not circularized (e.g. Molniya orbits), so tend to have shorter periods. Unless you count things in GEO graveyard orbits (which rise very, very slowly in the west -- their orbit is just slightly less than synchronous), I can't think of a significant population of artificial satellites that orbit slower than earth rotates.
- jakelazaroff 4y agoI thought it was an interesting article. Also, your comment breaks the guidelines: > Please don't post shallow dismissals, especially of other people's work. A good critical comment teaches us something. https://news.ycombinator.com/newsguidelines.html https://news.ycombinator.com/newsguidelines.html
- cjbgkagh 4y agoI think that’s shallow dismissal as in disagreement without substance, I.e. not adding much to an argument. Not dismissal as in a brief summary so you don’t need to read the rest.
- hooverd 4y agoIt's dismissive, but I wouldn't call it shallow...
- RedNifre 4y agoIt's a good comment because it summarizes the article better than the title does. Every article with a misleading title should have a top comment like that.
- dang 4y agoOk, we've replaced the title with a substring of the subtitle that is presumably less misleading. (in keeping with "Please use the original title, unless it is misleading or linkbait" - https://news.ycombinator.com/newsguidelines.html https://news.ycombinator.com/newsguidelines.html)
- RedNifre 4y agoThank you.
- Kranar 4y agoAre you claiming that OP, who posted a fantastic summary of the article, is being shallow? The guidelines are good for people to take into account on an individual basis, but they should not be used to police comments made by others.
- dehrmann 4y agoReminds me of a flight I had from the Nordics to California in winter. Because of the latitude, the plane was flying faster than the rotation of the earth. The flight left in the morning, so I got to watch the sun set in the east.
- hn_throwaway_99 4y agoTotally agree. I read through it and thought "this is not a hard concept". That said, I did think the last graphic in the article was really interesting, showing that with a highly elliptical orbit it's possible for a moon to both rise and set on the same side. The article could have been greatly improved by just showing those three planet/moon graphics and explaining the 3 possible states for each.
- kurthr 4y agoThere are satellites that use this (highly elliptical orbits) to spend most of their time (near perihelion) over a target area. One useful tool for thinking about orbits is that the swept area per time is constant so the farther out in orbit you are the lower the proportional angular velocity.
- mc32 4y agoThis can happen at a train station with multiple tracks or stationary car in a lot or multilane roadway. You're in the stationary one and the other train or cars move and if you're not thinking it can feel like you're going backwards.