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Stargazing Aaaannd.... here's Neptune

  1. Oct 15, 2016 #1

    Andy Resnick

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    Triton's retrograde rotation is also clear.

    Last night:
    DSC_6789_zpseuwubr9p.jpg

    Just now:
    DSC_6854_zpsrvusxdcq.jpg

    (5 seconds @ ISO 1600)
     
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  3. Oct 15, 2016 #2

    Vanadium 50

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    Um..you mean revolution, right? :wink:

    How can you tell from two pictures prograde that covers 90 degrees from retrograde that covers 270 degrees?
     
  4. Oct 16, 2016 #3

    Vanadium 50

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    And what (if anything) is the significance of the colors?
     
  5. Oct 16, 2016 #4

    Andy Resnick

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    which colors?
     
  6. Oct 16, 2016 #5

    Vanadium 50

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    Neptune (bottom right, right) is whiteish with a blue-violet halo. The stars are redder.
     
  7. Oct 17, 2016 #6

    Andy Resnick

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    Ah- that's 'longitudinal chromatic aberration' (LCA), sometimes called 'purple fringing'. You would see it on the stars as well if they were overexposed. Objects on either side of the plane of best focus will be tinged either purple or green (I forget which is which), and 'anomalous dispersion' glasses increasingly incorporated into lenses were developed to reduce LCA (flourite glass was used earlier). I believe that the 2x tele I use was designed to reduce LCA in the main lens, similar to tube lens design in microscopes.
     
  8. Oct 17, 2016 #7

    jim mcnamara

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    Great job.
    However I'm with Vanadium 50 on this - which dot is in retrograde? ...and other than that retrograde motion is known how can we see what you mean? Period of Triton's orbit is about 5.77 days - I'm looking really close to the brightest dot, Neptune. A fuzzy blob very close to Neptune moved about 70 degrees counterclockwise. Started at 9 o'clock -> went to about 7 o'clock. Wrong blob?
    360 degrees / 5.77
    62.39 degrees of arc per day ( 24 hours between images)

    300px-Voyager_2_Neptune_and_Triton.jpg

    - NASA photo on wikipedia.com
     
  9. Oct 17, 2016 #8

    Andy Resnick

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    Let's not be pedantic here- I'm not trying to re-discover something. I did not (and generally do not) intend to provide independent confirmation of a widely-known result.
     
  10. Oct 17, 2016 #9

    jim mcnamara

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    Intent: see if "dot was the right one." So I could see something I never saw before. Nothing earth shattering.... so which dot IS Triton?
     
  11. Oct 17, 2016 #10

    Vanadium 50

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    I'm genuinely curious. If you have multiple moons you can use Kepler's laws, but if you have only a few hours of good visibility per night, how can you tell the direction?
     
  12. Oct 19, 2016 #11

    Andy Resnick

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    Triton is the faint dot adjacent to the super-bright blob located at 9:00 on the top photo and 6:00 in the lower photo.

    I've also wondered how to tell the direction of motion when the moons are in-plane: Here's two shots of Jupiter from back in May, taken a few hours apart:
    upload_2016-10-19_9-13-1.png

    You can (barely) see that the great red spot has rotated, it's clear the moons have moved, but its very difficult to tell what's going on.

    Just a friendly reminder- if you want prompt responses, please uses quotes so I get a notification.
     

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  13. Oct 22, 2016 #12

    sophiecentaur

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    @Andy Resnick
    Can you give us some idea of the equipment and exposures used for this? I fear my Kodak box brownie might do as well as that. :wink:
     
  14. Oct 22, 2016 #13

    sophiecentaur

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    I am new to this game. Are you having a problem with a possible discrepancy between apparent 90° and expected 62.39°? I think you can get a whole range of apparent angles if not viewing along axis of orbit. It could be resolved with more views which could give an ellipsoidal locus - or not, depending.
     
  15. Oct 22, 2016 #14

    jim mcnamara

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    @sophiecentaur

    Several dots moved, AFAIK. I was not sure which one was Triton. Never saw the moons of Neptune like this, just NASA photos. And you are right, the edge on view Andy posted shows what you mentioned. You have to look for transits and occulations to figure out the orbit. This was mentioned in Jan Meeus book - the 1979 version of 'Astronomical Formulae for Calculators'. I also had a copy of 'Transits'.
     
  16. Oct 23, 2016 #15

    OmCheeto

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    Thanks!
    From my calculations, Triton, in your image, seemed too near to Neptune.
    It's maximum distance should be about 6.7 times the diameter of Neptune.
    distance to surface of Neptune: 330,000 km
    diameter of Neptune: 49,000 km

    But then I looked at the relative apparent magnitudes and determined that Neptune should be about 150 times brighter than Triton, so I decided that Neptune must be a bit "bloomy", and therefore too large. Is that correct?

    I noticed this effect in an image taken of Ceres last year from the Dawn spacecraft, when they wanted an image that included the background stars.

    Ceres is the bright spot in the center of the image. Because the dwarf planet is much brighter than the stars in the background, the camera team selected a long exposure time to make the stars visible. The long exposure made Ceres appear overexposed, and exaggerated its size; this was corrected by superimposing a shorter exposure of the dwarf planet in the center of the image. [ref]​

    Ah ha! After a bit of snooping, I found a "Triton Tracker".
    Another question I had was how Triton's orbit was aligned in relation to Earth.
    This kind of answers that question.

    On another page: Neptune And Its Maverick Moon Triton
    By: Bob King | August 26, 2015
    There's a panel of 6 images of Triton over 6 days that also show it: "Currently, Triton's steep tilt makes it trace out a nearly circular path, so it's visible nearly every clear night."

    Going back through the thread, to make sure I wasn't repeating anything anyone said, I noticed an anomaly in Post #7. Triton is too close to Neptune in that image. But the caption explained why; "Neptune (top) and Triton (bottom) three days after Voyager 2's flyby".
    The image was taken by Voyager 2, way back in 1989.

    Anyways, thanks Andy. I always thought Triton's were just big snails.
     
  17. Oct 23, 2016 #16

    sophiecentaur

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    I only spotted one at first but, now you mention it, there are smaller ones there too. This astronomy business seems to involve a lot of fuzzy images and (well informed) imagination / picking the most likely interpretation. I have seen a number of 'stars' that just won't focus and, when I look em up, the book tells me they're Galaxies. At least that's my story. (200p Dobs)
    Could that just be due to the spreading of the images due to the limitation of the optics?
     
  18. Oct 23, 2016 #17

    Vanadium 50

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    If something is closer than its maximum distance, where is the problem?
     
  19. Oct 24, 2016 #18

    Andy Resnick

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    My usual lens- 800/5.6 (400/2.8 + 2x tele), and a variety of exposure times: for Jupiter, the proper planet exposure is about 1/400s, ISO 100 while the moons require exposures of about 5s and ISO 400. The outer planets required about 1s ISO 200 for correct exposure, and the moons needed 8s ISO 2000.
     
  20. Oct 24, 2016 #19

    Andy Resnick

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    Lots of good discussion, let's see if I can provide some clarifications. Some of the issues appear related to the quality of my posted images- blooming and underexposure, but also the fact that I haven't posted 'final' versions.

    Blooming is a common problem- bright objects appear larger than they should.
    http://info.adimec.com/blogposts/ccd-versus-cmos-blooming-and-smear-performance

    On my images, this means the planet's bloom obscures nearby moons. The images of Jupiter + moons is a composite- the bloomed blobs of jupiter were replaced by separate images of correctly-exposed Jupiter. A source of error is placing the correct exposure image correctly- at the correct location in the overexposed image. Unfortunately, the bloom pattern is not circularly symmetric when the blob is off axis.

    For the outer planet images, the moons are barely observable- and this time of year the seeing is particularly bad. This makes it even harder to resolve the moons. Here's the result of stacking 6 images of Uranus on Saturday (10/22) night:

    10_22_930pm-1%20RGB_zpsaw7bo5ud.jpg

    Two moons are clearly visible- there may be a third, but it's partially obscured by bloom. Replacing the overexposed planet with a correct exposure yields

    10_22_930pm-2%20RGB_zpsutk84cue.jpg

    You can at least see the size of the blooming problem (puns absolutely intended).

    FWIW, here's what I have so far- 4 nights of viewing for Uranus, with the whole image scaled 50% to fit the planet's track in 800 x 600 pixels:

    uranus%2010_11%20thru%2010_22-1RGB_zpsndvozuha.jpg

    And 4 nights of Nepture, but this time the image is at 100%:

    neptune10_14%20through%2010_22%20RGB_zpsa44vfpb8.jpg

    You can kinda see the moons in the these images, but it's not great- some nights are better than others. My vision for these is that when I have a good-sized track (say over a month or two), I can go in and individually replace the bloomed planets with correct exposures, or even replace the moons if needed. And add dates, etc...
     
  21. Oct 24, 2016 #20

    sophiecentaur

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    That's a nice big piece of glass. (Did you spot the Freudian slip in my question? There's a missing "not".) I was considering getting an 80ED and launching into some astrophotography. From your comments and those of others, it's pretty clear that good results are only obtainable with skill and true grit. Astro montages are probably not as problematical as regular snaps with difficult backgrounds and moving subjects - but that's small consolation. Remember the doctored photos of Chairman Mao, bathing in the Yangtze river, published when his health was in doubt? ( Perhaps you are too young.) It's quite possible to make a similar hash of things, even with the lovely Photoshop.

    I've already seen that loads more stars emerge with stacking. Needless to say, since I took delivery of an Ioptron Tracker for my camera, I have had about 1 hour of clear sky at a suitable time but it seems to deal with star trails ok, afaics. It's going to be a long uphill struggle I think - with some significant expenses on the way. lol.
     
    Last edited: Oct 24, 2016
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