APOD: Andromeda on the Rocks (2016 Apr 19)

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APOD: Andromeda on the Rocks (2016 Apr 19)

Post by APOD Robot » Tue Apr 19, 2016 4:09 am

Please read first:
RJN wrote:Due to deception and subsequent non-cooperation, the APOD originally posted on this date has now been replaced. The below discussion does not apply to the current APOD on this date. We at APOD apologize the confusion and inconvenience.
Image Andromeda Rising over Colombia

Explanation: What's that rising over the hill? A galaxy. Never having seen a galaxy themselves, three friends of an industrious astrophotographer experienced an exhilarating night sky firsthand that featured not only the band of our Milky Way galaxy but also Milky Way's neighbor -- the Andromeda galaxy. Capturing the scene required careful pre-shot planning including finding a good site, waiting for good weather, balancing relative angular sizes with a zoom lens, managing ground lighting, and minimizing atmospheric light absorption. The calculated shot therefore placed the friends on a hill about 250 meters away and about 50 meters up. The featured single-exposure image was taken last July 26 at about 11:30 pm in Guatape, Colombia, about two hours from Medellin. The surrounding stars visible are all nearby in our own galaxy, while the small galaxy just above M31 is Andromeda's satellite M110.

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Re: APOD: Andromeda Rising over Colombia (2016 Apr 19)

Post by Boomer12k » Tue Apr 19, 2016 5:54 am

Interesting, but a bit disorienting with all the star trails... but admire the planning...

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Re: APOD: Andromeda Rising over Colombia (2016 Apr 19)

Post by Ann » Tue Apr 19, 2016 7:01 am

And the great-great-great-great-etc-etc-etc-etc-1010...-grandchildren of these three people, who may not look human at all, may actually be hit by Andromeda. Ouch.

Duck and cover!

Ann
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Re: APOD: Andromeda Rising over Colombia (2016 Apr 19)

Post by ACDC » Tue Apr 19, 2016 11:39 am

I'm not questioning the image but I'd like to understand how M31's core appears brighter than the lantern. If the lantern was "on" just for a moment, some movement would have been registered in the image, I'd think... How long was the shot, anyway?
Thanks,
Mel

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Re: APOD: Andromeda Rising over Colombia (2016 Apr 19)

Post by Asterhole » Tue Apr 19, 2016 11:56 am

Ann wrote:And the great-great-great-great-etc-etc-etc-etc-1010...-grandchildren of these three people, who may not look human at all, may actually be hit by Andromeda. Ouch.

Duck and cover!

Ann
Duck and cover, indeed! I like your bit of wry humor, Ann... Should there actually be sentient lifeforms in the Milky Way - or Andromeda for that matter to witness the head-on collision between the two, they would find it to be a rather mundane event, if noticeable at all.

And c'mon APOD -let's have some astronomy subjects again!
They're all wasted!

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Re: APOD: Andromeda Rising over Colombia (2016 Apr 19)

Post by jisles » Tue Apr 19, 2016 12:11 pm

Those are not star trails, because they extend approximately north-south. Near the top of the picture the star images are doubled. A double exposure? But the human figures appear sharp. Could this be another photoshopped fake?

hank

Re: APOD: Andromeda Rising over Colombia (2016 Apr 19)

Post by hank » Tue Apr 19, 2016 12:45 pm

if you zoom in a little bit you can see that the stars are double images, the camera was not steady or the Earth moved.

hank

Re: APOD: Andromeda Rising over Colombia (2016 Apr 19)

Post by hank » Tue Apr 19, 2016 12:51 pm

I took a second look at the people and it is possible the image was not a Photoshop as they are also somewhat blurred, in my opinion

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Re: APOD: Andromeda Rising over Colombia (2016 Apr 19)

Post by Cousin Ricky » Tue Apr 19, 2016 1:53 pm

I noticed right away that the stars smear north-south, meaning that they cannot be star trails, yet the figures are not similarly smeared. How is this a single exposure? Was the camera moving during the shot?

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Re: APOD: Andromeda Rising over Colombia (2016 Apr 19)

Post by Chris Peterson » Tue Apr 19, 2016 2:49 pm

Cousin Ricky wrote:I noticed right away that the stars smear north-south, meaning that they cannot be star trails, yet the figures are not similarly smeared. How is this a single exposure? Was the camera moving during the shot?
The pixel scale of this image is 14 arcsec/pixel. This star field moves across the sky at about 11 arcsec/sec. Given that we're probably looking at an exposure length of at least several seconds (and I'd think 30 seconds or more), tracking was probably required. If a tracking camera mount was used, but the polar alignment was off a bit, we'd see some declination drift (contributing to the N/S trailing). The double image effect could be noisy tracking or just mount vibration. (If there was no tracking, it could just be a very high ISO shot, short enough to produce little trailing but with a bit of wind buffeting.)

If I were setting up a shot like this, I'd be using a tracking mount, take my long exposure of the stars, and then get my foreground exposure by having my subjects light their lantern (or by using a flash). Nothing in this shot makes me think it isn't a single exposure.
Chris

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Re: APOD: Andromeda Rising over Colombia (2016 Apr 19)

Post by geckzilla » Tue Apr 19, 2016 4:25 pm

It's very easy to have some parts of an exposure blurred and others sharper if one part is only very briefly illuminated and during that illumination the camera remains still. Be it wind, quake, tracking misalignment, or some animal (human included) bumping the mount, we might never know for sure. Given the properties of the exposure we can say the people were illuminated only a fraction of the time, otherwise their light would have vastly outshone the faint Andromeda and they, too, would be blurred.
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twilight

Re: APOD: Andromeda Rising over Colombia (2016 Apr 19)

Post by twilight » Tue Apr 19, 2016 7:53 pm

Is this photo real? how is possible that andromeda more brilliant than lantern? only to take andromeda requieres at minimun 4 minutes exposition....afther that lanter and subjets will bright up to not see them......
and the size....andromeda is so tiny to the nude eye,,,how i get andromeda bigger than peple?

what do you think?
twilligt

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Re: APOD: Andromeda Rising over Colombia (2016 Apr 19)

Post by neufer » Tue Apr 19, 2016 8:10 pm

twilight wrote:
andromeda is so tiny to the nude eye,,,how i get andromeda bigger than peple?
Use a telephoto lens and put the peple on a far hill.
Art Neuendorffer

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Re: APOD: Andromeda Rising over Colombia (2016 Apr 19)

Post by BMAONE23 » Tue Apr 19, 2016 9:11 pm

Then have them stand still for the 4 minute exposure finally lighting the lamp for the last 1/2 second of light gathering

twilight

Re: APOD: Andromeda Rising over Colombia (2016 Apr 19)

Post by twilight » Tue Apr 19, 2016 9:37 pm

hi, but if you zoom andromeda, the people will zomm in equal proportion, no that bigger.

twilight

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Re: APOD: Andromeda Rising over Colombia (2016 Apr 19)

Post by geckzilla » Tue Apr 19, 2016 9:42 pm

twilight wrote:hi, but if you zoom andromeda, the people will zomm in equal proportion, no that bigger.
This isn't accomplished with simple zooming, but rather with a telephoto lens. It's a perspective trick. Here is an example which you probably wouldn't think twice about because the moon is so frequently photographed like this.
http://apod.nasa.gov/apod/ap160201.html

Here's a video using the same technique.
http://apod.nasa.gov/apod/ap140907.html
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Re: APOD: Andromeda Rising over Colombia (2016 Apr 19)

Post by Chris Peterson » Wed Apr 20, 2016 12:42 am

twilight wrote:hi, but if you zoom andromeda, the people will zomm in equal proportion, no that bigger.
The effect is unrelated to using a zoom or telephoto lens. Andromeda spans three or four degrees. Put some people between you and it, such that they also span a few degrees, and you'll get an image like this. Turns out that distance is about 250 meters.

Imagine you're looking at Andromeda. People very far in the distance will appear much smaller than the galaxy. As those people walk towards you, they'll get larger and larger compared with the galaxy (which doesn't change apparent size), until the people are right in front of you and are dozens of times larger.

The only reason you use a telephoto lens for an image like this is because the angular size of the objects is only a few degrees. To fill the frame, you need a long focal length (and therefore narrow field of view) lens. The effect would be the same with a wide angle lens, it's just that Andromeda and the people would only occupy a small area in the middle of the frame. Lousy composition.
Chris

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Re: APOD: Andromeda Rising over Colombia (2016 Apr 19)

Post by whwang » Wed Apr 20, 2016 2:33 pm

3 or 4 degrees of Andromeda only exist in rare photos or in catalogs, not in most pictures. Look at this:
http://subarutelescope.org/Topics/2013/07/30/
This camera on the 8.4-meter Subaru Telescope has a FoV of 1.5 degree, and it captures most of the M31. The size of M31 you can see in a reasonably deep amateur picture is no more than 2.5 deg, if you compare it with the M31 in the 1.5 deg Subaru image.

One thing you can do is to do a query on M31 and M110 in NED. Find their RA/Dec coordinates, and calculate the angular distance between them. The answer is 0.6 deg. If the distance between M31 and M110 is 0.6 deg, then the man in this APOD picture has an angular size of about 0.8 deg. If the true distance is 250m from the man to the camera, than how tall is the man if his angular size is 0.8 deg? This is a high-school level math problem. You can easily get the answer using a tangent function.

Let us know what you find about the height of the man, and then what you think about this APOD picture.

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Re: APOD: Andromeda Rising over Colombia (2016 Apr 19)

Post by rstevenson » Wed Apr 20, 2016 2:45 pm

Using your figures, the man is 3.49 m (or about 11.5') tall. Well, not impossible, just a tad unlikely.

Rob

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Re: APOD: Andromeda Rising over Colombia (2016 Apr 19)

Post by whwang » Wed Apr 20, 2016 3:17 pm

Looks like we have a world record. The previous record holder is this one:
http://www.guinnessworldrecords.com/wor ... man-living
and he is just 2.51m tall.

Wait, not just one, the two ladies in the APOD picture must be also taller than the previous tallest man in the world. One picture breaking the world record for three times. That's very very impressive.

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Re: APOD: Andromeda Rising over Colombia (2016 Apr 19)

Post by Chris Peterson » Wed Apr 20, 2016 3:20 pm

whwang wrote:One thing you can do is to do a query on M31 and M110 in NED. Find their RA/Dec coordinates, and calculate the angular distance between them. The answer is 0.6 deg. If the distance between M31 and M110 is 0.6 deg, then the man in this APOD picture has an angular size of about 0.8 deg. If the true distance is 250m from the man to the camera, than how tall is the man if his angular size is 0.8 deg? This is a high-school level math problem. You can easily get the answer using a tangent function.
The exact pixel scale, from an astrometric solution, is 14 arcsec/pixel. The man is ~200 pixels tall, or 2800 arcsec. Assuming a height of 1.8 m (and ignoring the small amount of foreshortening), that would place the people about 130 meters away from the camera.
Let us know what you find about the height of the man, and then what you think about this APOD picture.
I'd say that the imager reported a somewhat wrong distance between himself and the hill.
Chris

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Re: APOD: Andromeda Rising over Colombia (2016 Apr 19)

Post by whwang » Wed Apr 20, 2016 3:55 pm

An at least equally likely scenario is that the photographer combined two shots in Photoshop, misunderstood the realistic size of M31, and therefore came up with a wrong number when he tried to fake a distance.

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Re: APOD: Andromeda Rising over Colombia (2016 Apr 19)

Post by whwang » Wed Apr 20, 2016 4:05 pm

BTW, I personally don't think there is anything wrong with combining two pictures in photoshop. That should be allowed, as long as the photographer clearly states what has been done to the picture(s).

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Re: APOD: Andromeda Rising over Colombia (2016 Apr 19)

Post by geckzilla » Wed Apr 20, 2016 4:26 pm

whwang wrote:BTW, I personally don't think there is anything wrong with combining two pictures in photoshop. That should be allowed, as long as the photographer clearly states what has been done to the picture(s).
It's not a composite, though, unless there was a serious lapse in communication between the editor and Hugo. If it's written to be a single exposure in the description then it can be safely assumed that the photographer himself stated explicitly that it is a single exposure.
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Re: APOD: Andromeda Rising over Colombia (2016 Apr 19)

Post by Chris Peterson » Wed Apr 20, 2016 4:26 pm

whwang wrote:An at least equally likely scenario is that the photographer combined two shots in Photoshop, misunderstood the realistic size of M31, and therefore came up with a wrong number when he tried to fake a distance.
I don't consider that an equally likely scenario because there are no apparent artifacts suggesting this was done, and because the imager stated that it was a single image, and we're not given a good reason to doubt that claim. There's nothing particularly difficult about making an image like this in a single shot. And frankly, I think somebody faking it would have chosen a better deep-sky image.
Chris

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