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Can I see stars through the moon?

  1. Nov 4, 2012 #1
    Hey folks,

    A couple of weeks ago I took a photo of the moon, not sure if you will be able to see this in the image, but if you zoom in a bit after downloading it, you can see what I think are stars all over the background...

    ...The reason I say think is that I can see them through the shadow on the moon...Is this right? or is it something to do with the camera?

    I thought it might have something to do with gravity etc but couldn't really come up with an explanation, so thought I would ask here...

    Thanks

    http://postimage.org/image/yhcaxmi1t/
     
  2. jcsd
  3. Nov 4, 2012 #2
  4. Nov 4, 2012 #3

    phinds

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    Are you serious? The moon is solid. WHATEVER is in your pic, you are not seeing through a solid body and I find it hard to believe you could even ask.

    Probably dust on your lens.
     
  5. Nov 4, 2012 #4
    Well no offense, but I find it hard to believe that you could think that those specs were dust, they would have to be so small the sensor wouldn't even pick them up. Plus the light would be behind them so they would appear dark if anything, i thought that would be basic physics...

    Sensible answers only please, I realize it may be a stupid question, but I did highlight "think" in bold... Will accept other reasonable explanations... I figured some of you may know about optics...
     
    Last edited: Nov 4, 2012
  6. Nov 4, 2012 #5

    Pengwuino

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    In every astronomical image I've ever taken, you have to calibrate against dust (amongst other things). This is done when you take your flat images.

    My bet is probably on thermal noise, though.
     
  7. Nov 4, 2012 #6
    Yeah that makes sense, was just kind of hoping for it to be something cool, someone had mentioned to me that it might be gravity bending light...feel kind of stupid for believing them...

    I originally thought it was just noise, definitely not dust though, if you look at the meta-data it was taken at f9 so any dust on the lens or sensor would be blurry if anything...

    Yea, fairly confident it is noise now... Thanks for your response :) and your time....should have known better!
     
  8. Nov 4, 2012 #7

    russ_watters

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    Thermal noise, ie hot pixels is what those are.
     
  9. Nov 4, 2012 #8

    phinds

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    Sorry about being snippy before. Actually, the general concept of it being due to gravity is something that DOES happen and it's pretty cool, but the thing providing the gravity has to be WAY heavier than the moon. Google "gravitational lensing" to see what I mean.
     
  10. Nov 4, 2012 #9
    Yea no worries, would'nt be a forum without it :) I reacted pretty badly too...

    Thanks for the info, pretty interesting stuff, I knew I had heard something along those lines..Thats why I sort of went along with it...

    Thanks too, Russ...Its great to have an answer, Im usually photographing things a bit closer to home so never really experienced noise that looks like that..

    Cheers everyone :)
     
  11. Nov 4, 2012 #10

    davenn

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    You only need to see the noise across the lit area of the moon to realise how noisygrainy your image is. Its really no different an effect to the grainyness you would get on a film photo when you have under exposed. Lack of exposure time, incorrect f stop and ISO setting are your main culprits :)
    I would go as far as to say ALL the brightspots right across the image are probably ALL due to the noise and there are probably no stars visible there at all, anywhere in the pic

    You didnt say what focal length you were using ? I couldnt read the metadata
    but if it was a small f/l less than a few 100 mm then you image is zoomed somewhat and that will also increase the visibility of noise

    compare your pic to this one I did earlier in the year....

    attachment.php?attachmentid=52649&stc=1&d=1352085753.jpg

    thats 1000 mm f/l, f6.3 and 1 sec exposure at ISO 800

    cheers
    Dave
     

    Attached Files:

  12. Nov 5, 2012 #11
    Yes its taken with a 300mm lens @ f9, ISO800, 1/400sec that has been sharpened and cropped... im sure thats why its noisy... I really wasn't trying to win any awards though...

    Again, forgive my ignorance, my first time photographing the moon...the effect does kind of look like stars if you know virtually nothing about it.... like I said I'm used to photographing things that are right in front of me with strobes, flashes etc, so this effect the noise has produced isn't something I have really experienced before...

    All my decent glass is under 100mm, that was a very cheap 300mm lens as you can probably tell by the fringing around the moon....

    Thanks for your time though...Great photo too, I might invest in a telescope if I'm going to attempt this again, I clearly need the education lol
     
    Last edited: Nov 5, 2012
  13. Nov 5, 2012 #12
    The exposure times used for the moon are normally too short to capture stars. The moon would be completely washed out in an exposure long enough to photograph stars.

    Example image - Moon occulting the Pleiades:
    528215316_97647faa97.jpg
     
    Last edited: Nov 5, 2012
  14. Nov 5, 2012 #13

    davenn

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    Thats all cool... its always a learning experience :)

    try some more pics and drop your exp times down to ~ 1 second. with your 300mm, you could try a 2 x teleconverter, that will give you 600mm and a much larger image on the frame.

    Dont bother trying to photo a full moon, it will just be too glarey ( unless its a total eclipse)and washed out. Instead go for first 1/4 through to gibbous phase. Then you can get great crater detail along the terminator line like in my pic

    a good steady mount doesnt go amiss either ;)

    Dave
     
  15. Nov 5, 2012 #14
    Thanks Dave :smile:

    Will pick up a tele-converter and give that a go....Cheers for all the help!
     
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