Hi everyone,

I wanted to clarify a few things about looking at Neptune and its rings and satellites.

About the Neptune pictures I got just last week: here is an example of one of the challenges of using HST. I was assigned three orbits for Neptune. My plan was this: use one orbit to take a series of pictures in different filters (colors). Then wait about 6 hours. During that time, the planet would rotate about a third of the way around. Then use another orbit to take pictures through the same filters again. Then wait *another* 6 hours for the planet to rotate again, and use the final orbit to take the final series of pictures. This way, I could map out the entire atmosphere of the planet.

That was the PLAN. Here is what REALLY happened. Orbit 1 executed perfectly. Gorgeous pictures. Orbit 2 - perfect again. A whole new set of clouds! Orbit 3 - disaster. Halfway through the orbit, the guide star lock failed. This means that for some reason, the HST lost track of where it was pointing (normally it has sensors "locked" on nearby "guide stars" to know where it is pointed) . This is a potentially dangerous situation for the telescope, since without knowing where it is pointing, it could accidentally point at some bright star or even the Moon or the Sun - and that would destroy the sensitive light detectors! So to protect itself, if HST "loses lock" it automatically closes down the shutter. End of data.

So halfway through the Neptune pictures in the third orbit, the shutter closed, and I got pictures of nothing. It is not clear why the lock failed; these things just happen. So I did not get a complete map of Neptune. I may or may not be able to find a Great Dark Spot with this data. If I was unlucky, one may have been on the part of planet I was imaging during that third orbit. Maybe I was lucky, though. I don't know yet....

That is what I am working on today - looking at the new pictures from the first two orbits to see what is in there. It is very exciting to get brand new data! And that's something you will know about in the Spring, when your data is taken, no matter which planet you choose!

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