Celestia Forums

Ever since I implemented eclipse shadows in Celestia, I'd wondered if anyone had actually observed in eclipse shadow on Uranus. Apparently this new image from Hubble is the first ever picture of such an event:

http://www.spaceref.com/news/viewsr.html?pid=21908

Eclipse seasons on Uranus only occur twice during it's 84 year orbit around the sun, but there are a lot of eclipses during each of those periods--I think the article is mistaken to call them rare.

--Chris

chris wrote:Ever since I implemented eclipse shadows in Celestia, I'd wondered if anyone had actually observed in eclipse shadow on Uranus. Apparently this new image from Hubble is the first ever picture of such an event:

http://www.spaceref.com/news/viewsr.html?pid=21908

Eclipse seasons on Uranus only occur twice during it's 84 year orbit around the sun, but there are a lot of eclipses during each of those periods--I think the article is mistaken to call them rare.

--Chris

Here it is, just in time on July 26!

Bye Fridger

chris wrote:Eclipse seasons on Uranus only occur twice during it's 84 year orbit around the sun, but there are a lot of eclipses during each of those periods--I think the article is mistaken to call them rare.

I agree. I was quite suprised when I saw the list for 2 yrs of eclipses pop up in Celestia.

What's weird is that (at least up to Jan 2010) Ariel, Titania, Oberon, Umbriel are all listed as doing solar eclipses on Uranus in Celestia's eclipse finder, but Miranda isn't. I'd have thought Miranda would be just as able to block out the sun as the other four moons, is there any particular reason why it shouldn't?

Malenfant wrote:What's weird is that (at least up to Jan 2010) Ariel, Titania, Oberon, Umbriel are all listed as doing solar eclipses on Uranus in Celestia's eclipse finder, but Miranda isn't. I'd have thought Miranda would be just as able to block out the sun as the other four moons, is there any particular reason why it shouldn't?

In order to avoid some calculation, Celestia doesn't consider eclipses for very small objects. The occluding object must be at least 1/100 the size of the shadowed object. Miranda is just under this cutoff. I'll change the cutoff point, or perhaps make it configurable.

--Chris

chris wrote:

Malenfant wrote:What's weird is that (at least up to Jan 2010) Ariel, Titania, Oberon, Umbriel are all listed as doing solar eclipses on Uranus in Celestia's eclipse finder, but Miranda isn't. I'd have thought Miranda would be just as able to block out the sun as the other four moons, is there any particular reason why it shouldn't?

In order to avoid some calculation, Celestia doesn't consider eclipses for very small objects. The occluding object must be at least 1/100 the size of the shadowed object. Miranda is just under this cutoff. I'll change the cutoff point, or perhaps make it configurable.

--Chris

Ah, OK. I thought something weird was going on .

I forget, does Celestia differentiate between major moons (ie the named ones discovered from Earth) and minor moons (ie the tiny shepherd satellites etc)? Maybe you could use that to determine which ones are shown.

chris wrote:Ever since I implemented eclipse shadows in Celestia, I'd wondered if anyone had actually observed in eclipse shadow on Uranus. Apparently this new image from Hubble is the first ever picture of such an event:

http://www.spaceref.com/news/viewsr.html?pid=21908

When the last eclipse events took place about 40 years ago, the state of the art for astrophotography was poor. There was no way to compensate for the blurry atmosphere. Pluto's biggest moon wasn't discovered until 1978, and that discovery image was a blurry pear-shaped blob. So it was probably not possible to take a photograph of Uranus with sufficient clarity to resolve the shadow of a satellite.

chris wrote:Eclipse seasons on Uranus only occur twice during it's 84 year orbit around the sun, but there are a lot of eclipses during each of those periods--I think the article is mistaken to call them rare.

--Chris

I suppose they are considered rare because the eclipse seasons occur infrequently. Another factor that makes them rarer is the tilt of the orbit. Close to the equinox, the sun over Uranus' equator is moving rapidly and thus the eclipse seasons last for a relatively small time compared to the length of the orbit. By contrast, Jupiter spends a lot more time in eclipse seasons because its axis is almost perpendicular to the plane of its orbit.

The real fun with eclipse seasons is when the moons of Uranus start to eclipse and occult each other.

Hi !
Searching with Google, I found this site

http://lnfm1.sai.msu.ru/neb/nss/EveUra/EveUra.htm

where you can find dates and timings of all the relevant phenomena about Uranus Satellites.

Ciao
Pierluigi

I found a triple:



I had to modify minimum radius threshold so that Miranda would actually cast a shadow, however. Three shadows was the most I observed. Good thing too, since that's the max that Celestia will render for a single light source If someone can find a quadruple eclipse in our solar system, I'll up that number.

--Chris

celestia 1.5.0 beta 1 :p

chris wrote:I found a triple:



--Chris

Are those two shadows on Uranus from the two moons in front of it? It looks like the sun is way below the bottom of the image, I'd have thought the shadows would be more directly behind the moons given that Uranus looks full...