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General Astronomy >> General Observing and Astronomy

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Daniel Skinner
journeyman


Reged: 01/15/12

mirror projecting against full moon? new
      #5596098 - 12/30/12 12:45 PM

Hi All,

Quick facts:
* Explore scientific comet hunter
* 30mm eyepiece with 2x barlow

The other night I was out doing some viewing and pointed the telescope towards the moon to snap some pictures from my phone. This usually involves some slow adjustments with the phone camera pressed against the eyepiece where the moon will suddenly pop up if done just right.

What I noticed at some point was a partial moon and what seemed like a star field where the rest of the moon should have been. So I (painfully) looked through the eyepiece towards the moon and started rocking my eye left and right until I could see the circular moon disappear and be replaced with what appeared to be way more stars packed into the region of the moon then I've ever seen before.

As I thought about it, it seemed like the light being received was some how being projected against the moon and somehow rocking my eye the right direction allowed me to see everything.

So I held my head at that position and started moving the telescope (keeping the moon within view) and it looked like i was zipping across the sky.

So I tried snapping some pictures from my phone but they came out different than I was seeing them, but still telling.

https://plus.google.com/u/0/photos/101577546303489444718/albums/posts/5827792...

The stars aren't quite as prominent in the above picture but at the bottom, to the right of the "slideshow" button, there's an "options" button to download full size (still downscaled a little from original) and you can zoom in to see the somewhat blurry image of stars with lots of lens flare from the flash (couldn't get it any other way from phone).

When the flash goes off, it seems that the star field isn't just within the moon anymore but encompasses the entire view for some reason.

What I was hoping to get a picture of, and was quite the interesting site, was half the moon visible, and the other half replaced by quite a few stars packed in such a small area.

My question though is .. well .. what the hell? I'm not overly familiar with optics but would like to get the exact details of why this is happening. Even a brief explanation would be enough to point me in the general direction of reading material.

Thanks!


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Mark9473
Postmaster
*****

Reged: 07/21/05

Loc: 51N 4E
Re: mirror projecting against full moon? new [Re: Daniel Skinner]
      #5596144 - 12/30/12 01:09 PM

You seem to have drifted off focus so that instead you had the dust particles on one of the optical surfaces in focus.

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Daniel Skinner
journeyman


Reged: 01/15/12

Re: mirror projecting against full moon? new [Re: Mark9473]
      #5596154 - 12/30/12 01:16 PM

I thought it was dust too (and indeed need to clean the optics). But, when viewing directly, it was easy to identify dust b/c it was visually sitting on top of the optics.

And moving the telescope showed the stars actually moving, dust wouldn't have moved like that. Also unlike the picture, the points were small but very bright (very white).

I just can't believe it's dust (my first hypothesis) due to the various measures I took to confirm.

I feel like what I need now are better pictures.


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Daniel Skinner
journeyman


Reged: 01/15/12

Re: mirror projecting against full moon? new [Re: Daniel Skinner]
      #5596162 - 12/30/12 01:19 PM

And just to add (in case you were only saying that the dust was in focus and nothing more), the part I'm really interested in was when viewing directly, it was like a big circle in the sky, pitch black but packed tight with stars. No dust or anything else for that matter was visible to my own eye (except what looks like a strand of cotton in the middle of the eye piece).

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Dennis_S253
Pooh-Bah


Reged: 11/22/11

Loc: West Central Florida
Re: mirror projecting against full moon? new [Re: Daniel Skinner]
      #5597557 - 12/31/12 09:08 AM

Now this is wierd. Last night wasn't very good viewing, so I decided not to set up. I took a peek outside around 11:30 and it looked like there was a moon, and a 1/2 moon under it. Like a mirror shadow. It had something to do with my glasses because if I moved my head just right the mirror would disappear. It was like using a bad pair of bino's. The wierd part is I've never seen this before with my glasses on.

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GlennLeDrew
Postmaster
*****

Reged: 06/18/08

Loc: Ottawa, Ontario, Canada
Re: mirror projecting against full moon? new [Re: Dennis_S253]
      #5597716 - 12/31/12 10:48 AM

Your glasses would seem to be causing a ghost reflection. Even your corneas can cause ghosts. The size/intensity depend on such variables as eyepiece eye lens curvature and the separation between this lens and your eyeball.

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Daniel Skinner
journeyman


Reged: 01/15/12

Re: mirror projecting against full moon? new [Re: GlennLeDrew]
      #5597732 - 12/31/12 11:03 AM

One possibility I hadn't personally considered regarding my observation is that maybe it was dust and that the light of the moon was somehow being reflected by the dust to appear as stars by being so bright.

Panning the telescope produced a parallax effect reversed of what one might normally be presented with in media where the circular area of the moon moved slowly across the sky while the contents of the moon, which appeared as a field of deeply clustered stars, was zipping by.

I could imagine how maybe the moon's light was coming in and hitting only a particular point of the lens and then panning the telescope would adjust which dust particles were reflecting light, but my gut here says i wouldn't have seen the parallax as I did if its dust on the eyepeice, and the contents of the moon would have moved slower.

If i'm seeing dust on the front of the telescope, then I'd imagine the parallax effect i saw would have been at the same speed, moon panning versus moon contents shifting.

Hopefully I can get out there this week and figure out what's going on.


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GlennLeDrew
Postmaster
*****

Reged: 06/18/08

Loc: Ottawa, Ontario, Canada
Re: mirror projecting against full moon? new [Re: Daniel Skinner]
      #5598442 - 12/31/12 05:43 PM

I'm leaning more and more heavily toward the solution being: to clean your eyepiece. It sure looked like a veritable universe of dust bits was polluting at least one lens surface.

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SteveNH
professor emeritus
*****

Reged: 07/10/11

Loc: Millbrae, CA
Re: mirror projecting against full moon? new [Re: Daniel Skinner]
      #5598796 - 12/31/12 09:46 PM

Quote:

I just can't believe it's dust (my first hypothesis) due to the various measures I took to confirm.



Have you tried rotating just the eyepiece and then just the Barlow inside the eyepiece holder at the time these starry specks were visible? Bright objects like the moon, when slightly off axis and not necessarily visible in the field of view, can brightly illuminate fine dust that resides on any of the eyepiece's optical surfaces, as well as the internally and externally exposed surfaces of the Barlow's optics.


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Daniel Skinner
journeyman


Reged: 01/15/12

Re: mirror projecting against full moon? [Re: SteveNH]
      #5599181 - 01/01/13 08:12 AM

No, I didn't do that. I bet that would show it was dust on the barlow lens as I must have mislead myself by seeing dust on the eye piece sitting on top of the visuals.

I'll give this a shot tonight if clouds permit. Thanks for the tip.


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