Friday, 27 August 2010

Discovering asteroids

Thanks to Brad for discovering this amazing video.

For full details see the description by szyzyg on youtube, but essentially asteroids are highlighted white as they are discovered. The red asteroids are earth crossers, the ones we really need to keep an eye on, because this might happen!


Keera Ann Fox said...

Oh. My. It's rather cluttered out in space, isn't it.

Question: Mercury's and Mars' orbits are shown off-center relative the sun. Is that correct? If so, why?

Tom said...

Keera - good question and in fact it is correct. I don't know how accurately they portray things but Mercury and Mars have the most eccentric orbits of planets in the Solar System (Pluto's is larger but of course isn't a planet anymore!).

I don't know how much you know about orbits, so please forgive me if this is stuff you know. Planetary orbits are elliptical rather than circular and generally follow Kepler's laws of planetary motion. What this means is the "centre" of the orbits is actually one of the two foci in an ellipse, and neither are in the middle. Eccentricity in this case means how "stretched" the ellipse is and the higher the eccentricity the farther the foci are from the geometrical centre of the ellipse. The sun is at one of the foci and is therefore offset and noticeably so with Mars and Mercury.

Mars used to have a much more circular orbit but over time gravitational interactions with other planets have made the orbit more elliptical. The same is true for Mercury although its orbit is better explained with general relativity as it's so close to a large gravitational force, i.e., the sun.

The Earth's orbit is also off-centre relative to the sun but its eccentricity is much smaller, so not really noticeable in the video.

If you want to find out more I suggest googling "planetary orbits" and "Kepler's laws" although there is quite a lot of maths involved!

Keera Ann Fox said...

Thanks for your explanation, Tom! It'll do me just fine. I knew that our orbits are actually elliptical, but still with the Sun more or less centered in the orbit. Lazily, most illustrations showing the orbits, show them as circular. What I haven't seen before are the orbits of Mars and Mercury depicted with the Sun so off-centered.

Tom said...

Another thing they may have done, and I have no idea if they did, was include the inclination of the orbits. It's a top-down view and orbital inclination would affect that if they took it into account.

Mars has a small one, Mercury is quite large. Inclination is the angle of the plane of the orbit relative to the ecliptic (there are other measures as well).

You can picture this by imaging a planet with zero inclination, so the view in that video is just what the orbits are, and then imaging an orbit with 90 degrees inclination. In the latter case the orbit would be in and out of the video (if you can picture what I'm saying) and from the video's perspective the planet's orbit would look like a yo-yo.

So, any inclination angle would stretch the ellipse and distort things making the sun look even more off-centre.

As I said, though, I don't know if they took that into account;)


Maren aka hilobeads aka Palms, Etc. said...

Amazing video, thanks Tom and thanks Brad.