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This is a crazy idea I had... (but not so crazy because I found some proof that it's possible with the ASI990MM and ASI991MM pro)  I mean why should it not be possible with filters, right? I think this deserves an experiment. |
11.07
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Yes, though I question why anyone would want to do it. The only use I found was polar aligning in the day. I have a Paramount MYT and it uses 8-10 stars/planets for polar alignment. I discovered that when I got to a dark site I could get the polar alignment done during the day. With my 3nm OIII filter I could make out stars down to Magnitude 2 or maybe a bit brighter. I would manually jog the mount to center the star and them enter it in the model for polar alignment. Between the bright stars and planets I could usually get the polar alignment done before sunset. This is not a accurate as plate solving for the alignment but it gets you close. |
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Kevin Morefield: That's amazing |
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The sentence in your screenshot looks wrong to me, because they are referring to three completely different attributes of the sensor (sensitivity, spectrum and definition) as one and the same. I wouldn't take it too seriously. Remember: the sun is a star. There is little qualitative difference between starlight and daylight, it is only a question of quantity. Even if a star has a different spectrum and emits say 50000% more green light than the sun, the green light that reaches us from the sun still is thousands of times stronger. So filters will *not* help much. You can capture or even see with the naked eye bright stars and planets during sunset to early dusk and late dawn to sunrise, under what technically constitutes daylight. But the result is not too good, unless you are making flat frames  .I actually do capture Polaris (which is a little brighter than 2mag) as well as 10 or 12 stars in its general viccinity while setting up the gear, minutes after sunset. I use a 533 sensor close to 0 gain and the stars show up on 1-2 second subs. The image is good enough to focus accurately but not good enough to polar align, this is only possible after "mid-dusk" if I may coin the term. Cheers, Dimitris |
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Yes, absolutely possible. Last year, on May 9, I set up my 60 mm Apo at f/8.6 with a Canon EOS 90D and photographed the lunar occultation of eta Leo (3.5 mag vis). Surprisingly, the star was visible with exposure times of only 1/320 sec @ ISO 200. The altitude of the sun was roughly 2.5° when the occultation started. Juergen |
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| When I was much younger than I am I could see Sirius in broad daylight (not sunrise or sunset) as well as Venus if conditions were right and know where to look at exactly. Alas, this is gone. Reportedly one of Japanese top aces could navigate in broad daylight using Conopus during WWII. |
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andrea tasselli: *Andrea, I found that I could see a couple bright stars during the daylight, not at dusk or dawn. The eyes (and brain) make this difficult. You have to know exactly where to look, and your eyes struggle because they tend to wander when looking at a large blue field of sky. Our eyes make many small stutters when viewing such fields. But if you are lucky to lock onto a star, yes, it can be done. When I am using my NIR camera with a 950nm edge filter, I have no problem seeing stars during the day. I suspect that this would also work well using a standard response camera and the typical NIR filters used for planetary imaging, such as done for Venus. Just getting a simple terrestrial image using my setup will show a very dark full daylight sky. Have a look at my post:  New Toy(s), "First Light", IR camera The lower left image shows such a terrestrial view with my NIR camera and the 950 edge filter. Note the image was taken through my window and I was not trying to see stars. But I have seen stars through the setup during the day. I have not tried to use this for daytime polar alignment, but I think it would work very well. If I had my guide scope well aligned to my main scope, I would then use the NIR camera and this filter to do the alignment. The NIR camera is a small format camera and works well as a guide scope. The NIR capabilities (typically in the NIR below 950 with the provided filters helps with guiding because NIR images are less affected by "seeing"). |
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Alan Brunelle: That is interesting. Looking at its response curve the ASI991MM also looks to be most sensitive up in the NIR. I've thought about trying NIR but not yet quite sure what I'd do with it and will be interested to see what uses emerge for these particular new toys. |
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| I once took some daytime pics of the Orion Nebula and its Trapezium... https://vanderbei.princeton.edu/images/NJP/m42daytime.html |
11.57
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When there are no clouds, you can see Jupiter and Venus with naked eyes in day time, if you know where to look. You can use a calibrated goto scope to point at them and then follow the pointing direction to try seeing them with naked eyes. Then you can try a few brightest stars this way. Even if you can't see them with naked eyes, you should be able to easily see them in a 7x50 finder scope. If you can see such stars in a finder scope, there is no reason you can't image them with your main scope. It should be super easy. The only potential problem is when your camera does not have a very fast shutter, the sky can saturate the sensor. If this is the case, a narrow-band filter would help. Then the question is why? Why would anyone want to image a star in day time? I guess, for fun? Of if one summer Betelgeuse explodes, I believe many people will try to image it in day time. |
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| I too have wondered this, perhaps using an H-alpha solar telescope and long exposures, it could be possible with a regular astro cam in broad daylight. Has anyone tried this? |
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11.57
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Brian Fulda: been there. done that. very easy. (open the image in a new window or tab to see the details.) asking whether this is possible is irrelevant. what's relevant is asking why you want to do this.  |
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On May 29, 1919 astronomers observed stars near the eclipsed sun in a test of the Theory of Relativity....does that count? Alex W |
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Brian Fulda: Unlikely, Ha solar scopes are made for one thing, the sun, at -26 mag and just 93 million miles away. If you can point to any bright star, you should be able to image it with just about any camera. |
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Bob Lockwood:Brian Fulda: Unfiltered, though? I'd imagine you need at least some kind of filter, Ha ideally, to separate out the star from the background daytime sky. Looks like that's the technique @Wei-Hao Wang used. I think it would be possible with a solar scope, just much longer exposures needed. I will try it soon. Side note, the SR-71 Blackbird used something called the Astroinertial Navigation System (ANS) which used stars as a navigational aid during flight, even during daytime. Granted, they were flying at 80,000 feet, so a lot closer to space, but still pretty cool they had tech that could see stars during daytime back in the 60s |
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Brian Fulda:Bob Lockwood:Brian Fulda: *If you read further up the thread I described the use of NIR filters for this purpose. While my description mostly centers on the use of a 950 edge filter used with a relatively inexpensive NIR sensitive camera (see QHY), there are other such filters with somewhat shorter wavelengths that are used routinely for planetary imaging and regular response cameras. These are a much broader filtration choice and should yield a much stronger signal than using an H Alpha filter. While I'm sure H alpha would offer a slight advantage, it's still in the visible range and extremely restricted, thereby wasting much of the longer wavelength light. And I've seen Venus and at least one star optically during full daylight There is no question that at least some stars can be seen during the day even with broadband. What I am suggesting is that using NIR filtration should bring into play many more stars during sun-up. But why? Still don't have that answer. But I may try! Just need some time! I can imagine a widefield terrestrial image of sky, sun, and the Pleiades setting over a mountain range shot in NIR! Could look otherworldly! |
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I'd imagine you need at least some kind of filter, Ha ideally, to separate out the star from the background daytime sky. Looks like that's the technique @Wei-Hao Wang used. I think it would be possible with a solar scope, just much longer exposures needed. I will try it soon. Hi, To be clear, the filter I used is just to avoid saturation of sky background during the exposure time that my camera can afford (shortest being 0.05 second), like I said in my first reply. It doesn't really help to separate star from sky. For example, if an H-alpha filter can attenuate the sky by 10 times compared to a red broad-band filter, it attenuates the star by 10 times as well. An H-alpha filter only helps to separate target from background if the target emits H-alpha line strongly. Stars are not this kind of objects. A narrow-band filter does not help to separate stars from the bright background sky. Like Alan said, the best filter will be a near-IR one. The daytime sky is the brightest in the blue (that's why the sky is blue) and less bright in the red. It's even less bright in the near-IR. So if you use a near-IR filter, you should get the best star-sky contrast. This is why I used H-alpha to avoid saturation but not OIII. If you have a camera that can do very short exposure to avoid saturation, you don't need a narrow-band filter. Just a broad-band filter will do. A near-IR one is the best, then a red one. Don't use a green or blue filter. |
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Just did some daytime "stargazing" and see what's the limit of our CDK20 at a high-mountain site. 4th mag stars are easy targets (second screenshot). Once it reaches mag 4.5 (e.g., first screenshot), it becomes challenging. 5th mag stars are possible, but the signal is weak and image would look dirty. Focusing in day time is a major challenge. Using a 3rd mag star, I found its sharpness quite indistinguishable in +/- 200 micron focus range. (In night time, we can easily narrow down the focus to well within +/- 50 micron.) This is clearly caused by turbulence in the air. In series of exposures (exp time = fractions of a second), I can never measure star FWHM better than 4". (The night time seeing of this site is often better than 1.5".) This poor day time seeing does not only prevent accurate focusing, it also decreases limiting magnitude. If we can somehow get a 2" seeing in day time, I believe our system can reach a limiting magnitude of about 6.0, just like naked eyes under a dark sky. In this test, I used an H-alpha filter. Like what I said in the earlier post, this filter is just to suppress light intensity (of both the target and the sky background) so the sky doesn't get saturated within the shortest exposure time (0.05 sec) of our camera. Because sky is blue, and H-alpha is red, so this filter has better sky-suppression (as oppose to OIII, the other NB filter that we have). I think what will be interesting is to use a broad-band I filter. It's in the near-infrared, so it has even better sky suppression than H-alpha. And if we observe red stars rather than blue stars, the star/sky contrast will be the highest in the I filter. I didn't try it because I is a broad-band filter. Although it offers the best star/sky contrast, the overall light intensity is too high and the whole CMOS will get saturated with its shortest exposure time. A firmware update of our camera may push the shortest exposure to 0.0002 sec. Once we have a chance to update the firmware, we will give the I filter a try, and see if we can detect very faint stars (like 7th mag) in day time. Why doing all these? No particular reasons. The pictures are not pretty, and the data do not have science values. It's just for fun.   |
