Re: Occultation of Saturn
- From: Claudio Grondi <claudio.grondi@xxxxxxxxxx>
- Date: Sat, 03 Mar 2007 17:30:39 +0100
Pete Lawrence wrote:
On Sat, 3 Mar 2007 13:21:54 -0000, "Dave Smith"Thank you both Pete and Dave for your response.
I have compared the third pictureHi Claudio
available from the page:
with the composite one done by Pete:
You can see what I mean at:
How does it come, that the moon surface appears so different?
Am I missing something here?
That is very interesting. I strongly suspect that the difference in Moon position is due to the difference in location between Maldon, Essex where I took my picture and Selsey where Pete took his. Pete I believe, from his location did not see Saturn totally disappear whereas from Maldon it disappeared for nearly half an hour. Even though the relative position of Saturn compared with the Moon will not be great, as it is a grazing or near grazing event then the position on the Moon's surface where it appears and reappears will be quite sensitive to location. E.g. For Pete in Selsey there is only one position on the Moon's surface where Saturn will be at its closest. From Maldon the entry position and exit position were quite different.
This is what it did for me...
Now I know what I was missing and some more:
- first I haven't took the position on Earth from which the shots were made into consideration - I made a comparison between two different perspectives what was just not appropriate.
- the next problem I have run into is, that I have not looked at the time at which the pictures were made I have compared - Pete's was made at 2:52 and Dave's at 2:59 - I just assumed, that same position of Saturn in relation to the Moon means, that the pictures were taken at the same time ...
Now, after I got aware what was wrong with my comparison, I realized, that in fact I should know about such effects from what I know about solar eclipse events. I have to admit, that I am very surprised, that the effect could be so significant already for so small differences of locations within England as between Selsey (West Sussex) and Maldon (Essex), so I assume, that most of the effect was caused by the 7 minutes time difference between the shots and not by the difference in locations.
I suppose I have to dig much deeper into it in order to get a better feeling for such things, as I have to admit, that my intuition still resist to accept the given explanation.
Could it be, that the same piece of surface of the moon can look very different on different pictures depending on some other factors I am still not aware of?
What I have learned from this lesson?
Pictures of objects in relation to the Moon should contain beside the date, time also the exact location from which the picture was made in order to be useful for comparison purposes.
I expect, that this is exceptional to pictures involving the Moon, as I suppose, that the position on Earth from which a picture was made doesn't have a significant effect on pictures of solar system planets (and their moons) even if there is maybe a very slight effect on their position relative to the stars.
I have googled for 3D models of solar system helping me to adjust my intuitive expectations to the reality, but the best I came up with yet is the magnification feature in Stellarium. This helps much, but it does not show enough Moon surface details (yes, I was able to watch the occultation of Saturn in Stellarium).
Is it possible to have a much more detailed Moon surface in Stellarium and if yes how can this be achieved?
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