APOD: Milky Way in Moonlight (2016 Apr 23)

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APOD: Milky Way in Moonlight (2016 Apr 23)

Post by APOD Robot » Sat Apr 23, 2016 4:11 am

Image Milky Way in Moonlight

Explanation: A waning crescent moon, early morning twilight, and Al Hamra's city lights on the horizon can't hide the central Milky Way in this skyscape from planet Earth. Captured in a single exposure, the dreamlike scene looks southward across the region's grand canyon from Jabal Shams (Sun Mountain), near the highest peak in Oman, on the Arabian Peninsula. Mist, moonlight, and shadows still play along the steep canyon walls. Dark rifts along the luminous band of the Milky Way are the galaxy's cosmic dust clouds. Typically hundreds of light-years distant, they obscure starlight along the galactic plane, viewed edge-on from the Solar System's perspective.

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Boomer12k
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Re: APOD: Milky Way in Moonlight (2016 Apr 23)

Post by Boomer12k » Sat Apr 23, 2016 6:05 am

Moonlight, and YOU, baby....

Great Pic...
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Joules
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Re: APOD: Milky Way in Moonlight (2016 Apr 23)

Post by Joules » Sat Apr 23, 2016 1:54 pm

Nice shot. Tafreshi must have a big lens and a high megapixel camera to keep the moon overexposure from making a big nasty blob.

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Re: APOD: Milky Way in Moonlight (2016 Apr 23)

Post by Joe Stieber » Sat Apr 23, 2016 6:04 pm

Joules wrote:Nice shot. Tafreshi must have a big lens and a high megapixel camera to keep the moon overexposure from making a big nasty blob.
I would submit the moon actually is quite a blob in this picture. It's impossible to tell from the picture itself that it was a crescent, let alone which way the crescent is facing. The number of pixels in the camera has little to do with it. It's just a simple fact that the dynamic range here is way too great to capture a well-exposed crescent and the background starry sky at the same time with a single exposure, so you let the moon go and expose for the sky (and this case, the foreground too).

BTW, the EXIF data from the picture indicates it was taken with a Canon EOS 6D digital SLR camera (nominally 20 megapixels) and was exposed 15 seconds at ISO 3200. No lens information was provided (focal length or f/stop), but based on spacing of the Moon, Saturn, Mars and Antares, I'm guessing it was in the neighborhood of 20 mm focal length, i.e., a very wide angle lens for the "full frame" sensor in the 6D.

The EXIF data also indicates it was taken on 3/3/2016 at 5:56 pm. The afternoon time is clearly wrong. Comparing the picture to a SkyTools chart, the position of the moon with respect to the handle of the Teapot asterism in Sagittarius as well as the moon with respect to Saturn and Mars, I think it was taken sometime around 5 am on March 4, 2016 (the approximate start of astronomical twilight since sunrise was around 6:30 am for this location). Perhaps it was taken even later into twilight to illuminate the foreground, possibly 5:56 am if the camera's clock was exactly 12 hours off (due to an am/pm mix-up). In any case, the moon was about 30% illuminated at the time.

heehaw

Re: APOD: Milky Way in Moonlight (2016 Apr 23)

Post by heehaw » Sat Apr 23, 2016 11:54 pm

It is truly awesome that if you can get to a dark enough location, you can clearly see our Galaxy laid out before you. Parts are blocked by clouds of interstellar dust, but the main features of the Galaxy are clearly visible to the unaided human eye. And in the southern hemisphere, what appear to be two detached fragments of the Milky Way appear, and they are the Magellanic Clouds, small galaxies spiraling around our Galaxy. And in the northern hemisphere, you can see, if you have a dark enough sky, a patch that you know is the great Andromeda nebula, a galaxy that long after you and I are gone, will collide and merge with our own Galaxy. Isn't it lovely that we know these things? And think of your ancestors, and mine, say 10,000 years ago, looking at these same things with wonder of what mysteries they were manifestations. OK! What new insights will your descendants and mine have, 10,000 years from now? What will they think of US? At least we went to the Moon, and we found the Higgs, and we found gravitational waves: not too shabby, I think!

JoeTourist

Re: APOD: Milky Way in Moonlight (2016 Apr 23)

Post by JoeTourist » Sun Apr 24, 2016 5:04 am

Babak nailed this night sky shot of the Milky Way over Wadi Ghul, aka the Grand Canyon of Arabia at Jebel Shams in Oman, but I think my shot from the exact same spot taken in the early morning light is pretty good too! 8-)
Image
http://photos.joetourist.ca/jebelshams/e484aeab

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Re: APOD: Milky Way in Moonlight (2016 Apr 23)

Post by DavidLeodis » Sun Apr 24, 2016 12:23 pm

Joe Stieber wrote:
Joules wrote:Nice shot. Tafreshi must have a big lens and a high megapixel camera to keep the moon overexposure from making a big nasty blob.
I would submit the moon actually is quite a blob in this picture. It's impossible to tell from the picture itself that it was a crescent, let alone which way the crescent is facing. The number of pixels in the camera has little to do with it. It's just a simple fact that the dynamic range here is way too great to capture a well-exposed crescent and the background starry sky at the same time with a single exposure, so you let the moon go and expose for the sky (and this case, the foreground too).

BTW, the EXIF data from the picture indicates it was taken with a Canon EOS 6D digital SLR camera (nominally 20 megapixels) and was exposed 15 seconds at ISO 3200. No lens information was provided (focal length or f/stop), but based on spacing of the Moon, Saturn, Mars and Antares, I'm guessing it was in the neighborhood of 20 mm focal length, i.e., a very wide angle lens for the "full frame" sensor in the 6D.

The EXIF data also indicates it was taken on 3/3/2016 at 5:56 pm. The afternoon time is clearly wrong. Comparing the picture to a SkyTools chart, the position of the moon with respect to the handle of the Teapot asterism in Sagittarius as well as the moon with respect to Saturn and Mars, I think it was taken sometime around 5 am on March 4, 2016 (the approximate start of astronomical twilight since sunrise was around 6:30 am for this location). Perhaps it was taken even later into twilight to illuminate the foreground, possibly 5:56 am if the camera's clock was exactly 12 hours off (due to an am/pm mix-up). In any case, the moon was about 30% illuminated at the time.
The time given in the Exif data also confused me as the explanation (and in the caption to the image brought up through the 'the dreamlike scene' link) it states "A waning crescent moon, the emerging morning twilight" so thus not p.m. I find it adds interest to know at least the local date/time when an image was taken so I wonder what was the definite date/time?

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Re: APOD: Milky Way in Moonlight (2016 Apr 23)

Post by Joe Stieber » Sun Apr 24, 2016 7:00 pm

DavidLeodis wrote:The time given in the Exif data also confused me as the explanation (and in the caption to the image brought up through the 'the dreamlike scene' link) it states "A waning crescent moon, the emerging morning twilight" so thus not p.m. I find it adds interest to know at least the local date/time when an image was taken so I wonder what was the definite date/time?
Based on the moon's position, I'm still pretty sure it was taken on the morning of March 4, 2016, but the more I think about it, the more I suspect it was closer to 6 am local time. That would put it near the start of civil twilight. The brighter twilight then would provide the illumination needed to show the foreground canyon. I suppose the trick is to find the balance between enough twilight for the foreground, but not so much as to wipe out the background sky, which is already compromised a bit by the moon. Most likely, a number of exposures were taken starting before the onset of twilight. Then it's a matter of going through dozens of pictures to find the best one.

I have a Canon 6D too, and it has a built-in GPS which can update the camera's clock, if the GPS is activated and it's set to do the update. This, of course, would provide an accurate time stamp. However, I have found (as have others) that when the internal GPS is activated, even if the camera is switched off, the battery runs down in a few days (a quirk of the 6D, which is otherwise a fine camera). Therefore, one normally turns the GPS off when not using it, and back on when using it -- but of course, we all forget sometimes. However, even allowing that camera clocks (without GPS assist) are not all that precise, being 12 hours off would be an unusually large error for simple clock drift. Since Tafreshi apparently travels a lot, perhaps it was inadvertently still set to some distant time zone. I know a guy who travels a lot, so he sets his camera clock to UT to avoid the problem of constantly re-setting it for different local times, or having the wrong local time. It would indeed be interesting to learn what happened with the camera's time, as well as what the actual local time was for this picture.

BTW, some of my astronomy associates probably get tired of hearing me say it, but I'm always exhorting them to make sure their camera clocks are set correctly, especially at daylight time changes. In particular, even if they recently set it, I suggest they take a picture of a good clock page, such as the Official NIST Time or the USNO Master Clock, so they can go back and establish any offset between the EXIF time and what the reference clock shows in the image.