From the series of avi’s covering the recent occultation of Uranus by the Moon, I plotted, as faithfully as I could, the positions of Uranus against the lunar limb, to show the “path” of Uranus as it approached the limb.
Image inventory:
The disc of Uranus processed in Registax from an avi leading up to the occultation.
The normally exposed lunar limb from an avi immediately after the disc of Uranus disappeared behind the lunar limb.
A series of frames from several avi’s leading up to the occultation. These showed the position of Uranus relative to the grossly over exposed lunar limb.
The ‘scope was tracking on Uranus and the lunar limb crept up on the planet’s disc in each successive avi.
When I plot the disc of Uranus against the correctly exposed lunar limb, by overlaying frames from the approach avi’s, to match the lunar limb profile features, the resultant path of Uranus appears curved, getting steeper towards the point of contact.
I wasn’t expecting this?
EDIT: Added an image showing how I performed the registration.
I think what you are seeing is the result of the differences in proper motion between the two objects. It looks like Uranus is curving, but that is an optical illusion. I believe it due to the fact that the moons orbital radius is so much smaller than Uranus and it's obit is tilted differently to Uranus in respect to our viewpoint, that the moon is "dropping away" from the orbit of Uranus. Try overlaying you images with Uranus going straight, and moon will drop away.
Fantastic images Dennis, I love the education I'm getting (for free).
I was wondering what the event looked like as from here I had a good cover of Clouds!
I wanted to look with Bino's, would I have seen Uranus?
Rgds J
And an excellent explanation of the curved locus of Uranus, Paul! I noticed that from Dennis's other post. Like Dennis I didn't expect that, so I had it on my list of things to ponder when I finished browsing posts... then I found this .
It seems surprising to me though that the rate of curvature of the locus should appear to change so much so quickly as the conjunction approaches... I'm sure you're on the right track, it's just that the movement of the moon between the first and last images is not large (a few degrees only?)... hmm, just thinking out loud here really!
I think you will find that if you were to accurately measure the change in position for each image the drift/time will be linear (or as close as over the imaging time to make little difference). It only looks curved due to the the change of frame time. ie time from frame 1 to 2 - 5 min, 2 to 3 - 2 min, 3 to 4 - 30 sec etc (these are only demonstration times to give you the picture/idea)
Well I just did that little line drawing exercise and I was way off beam. There is a continual change of angle. I still think I'm on the right path, I'll just have to think about it a bit more.
There is another factor in this that I hadn't considered either. The "apparent" rotation of the moon. I have just run that morning through Starry Night and it is quite easy to see the effect with the moon moving at a different angle to Uranus (use the RA and DEC grid as a reference) and the "apparent" rotation of the moon as it moves from east to west. Due to this rotation the "top" reference mountain will be moving away from Uranus adding to the "dropping away" effect . Make sure you use the moon as your "center" point and not Uranus. If you use Uranus as the "center" point you get the "dropping away" effect.
Last edited by [1ponders]; 10-09-2006 at 12:31 PM.
Well I just did that little line drawing exercise and I was way off beam. There is a continual change of angle. I still think I'm on the right path, I'll just have to think about it a bit more.
Atmospheric refraction in the Earth's atmosphere, could be something to consider if the moon was closer to the horizon jacob, and their positions were right, but this image was taken around 00:45 in the morning so the moon and Uranus would have been about 12 degrees to the west of a line drawn north and south (meridian) so it's not likely.
No atmospheric refraction for the moon as it has no atmosphere to speak of.
I've attached a screen dump of the relative angles of the Moon's and Uranus' orbits so you can see where part of the effect comes from. Another aspect of this, of course, is Dennis' alignment on the features of the moon. Because the moon is dropping away and "rotating" visually, then aligning features on the moon will have an additional effect of "pushing" Uranus higher (I'd be lost without " " , will someone please make me an " " smilie )
Gee Paul - you missed your calling.....you should have been a planetary scientist. I've just returned from an outing so I'll dig up the avi's and post a composite image with the times on it.
Thanks to all the people who lent their brains to solving this "mystery" - a hard ask for a Sunday morning!
Doesn't matter Dennis. I've just checked out your other post and it appears that features on the moon move in a downward direction as Uranus moves closer to the moon.
![[1ponders]'s Avatar](../vbiis/customavatars/avatar45_9.gif){kind=avatar}
.....top work Dennis matching a fine image with an astronomical event is just great 
.
, will someone please make me an " " smilie 
