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Anyone know about taking astronomical photographs? There's one such photo at the top of this article. 1. The night's sky never actually looks like that. Is

Anyone know about taking astronomical photographs? There's one such photo at the top of this article. 1. The night's sky never actually looks like that. Is it simply that the exposure was long so that the brightness of each object is enhanced? How long would the exposure have to be? 2. What is that pinkish nebula-like band/arc that the photo is centered around?

pvg 9y ago
That is a long-exposure shot although the sky does really look like that if it's dark enough - just not quite that colourful. Here's an attempt by a photographer to recreate the effect: https://vimeo.com/113287920 https://vimeo.com/113287920 The band in the photo is the milky way.
- PetitPrince 9y ago
  > although the sky does really look like that if it's dark enough I agree. Additionally, I assume most people here on HN live on a place that is heavily light-polluted, see https://www.lightpollutionmap.info https://www.lightpollutionmap.info . If OP happen to pass by a place with low light pollution, I encourage him/her to stay and watch the sky for a while (30 minutes ?) so that the eyes can adapt to darkness. It's really a neat experience.
  - jakeogh 9y ago
    Mt. Graham, east of Tucson. Worth it. http://www.darksky.org/ http://www.darksky.org/
Sharlin 9y ago
It is a real shame that so many people don't recognize the Milky Way, by having lived their whole lives under light-polluted skies. But yes, even an optimally dark sky isn't that colorful to a human eye. That's because human low-light vision, provided by rod cells, is almost entirely monochromatic. A camera sensor doesn't have such limitations. You do need an exposure time of several seconds at least, but first and foremost you need to get away from light pollution. No amount of exposure time is going to help you inside a large city; the sky just comes up ugly orange-gray. To a totally dark-adapted human eye in an optimally dark location the night sky is a sight to behold.
Spellchamp 9y ago
Hello, not a direct reply to your questions but you'd be right to say that most photos you see of space are inaccurate for colour. We call them "false colour" images. Typically what you'll do is take images of the same object with a telescope at a variety of different wavelengths. The basic pattern is to use 3 images, and then use each one to represent a different colour from red, green and blue. Then layering one on top of another you can create an image that looks like the bright and colourful ones you typically see of nebula/pulsars etc. This way you get lots of detail, since different parts of the celestial bodies are only visible at certain wavelengths. So a single wavelength image would be over saturated with certain effects. So even though these are technically "false" colour images of space. There is a scientific reason for doing it. Not saying that the photo in the article is false, I think it's just had a long exposure time. Anyway, hope this helps understanding of astrophotography in general.
Angostura 9y ago
That's the milky way, though I'm sure that's not visible from anywhere in earth like that. Whenever I've seen it, it has been a band across the sky, not an arc. Perhaps a composite using a wide-angle lens? One of the other replies to your comments talks about false colour photography, however this one, I think is probably true colour with long exposure. The problem you have is that for very dim objects the colour-sensing 'cone' cells in your retina pretty bad. In low light conditions you're much more reliant on the rod cells, which are monochrome only (and more abundant in the periphery - if you are ever looking at a dim object, try looking at it from the corner of your eye).
- eric_h 9y ago
  > Whenever I've seen it, it has been a band across the sky, not an arc That photo is most certainly a composite of some sort. It was also taken in the Southern Hemisphere (Australia).

pvg 9y ago

That is a long-exposure shot although the sky does really look like that if it's dark enough - just not quite that colourful. Here's an attempt by a photographer to recreate the effect: https://vimeo.com/113287920 https://vimeo.com/113287920 The band in the photo is the milky way.

PetitPrince 9y ago
> although the sky does really look like that if it's dark enough I agree. Additionally, I assume most people here on HN live on a place that is heavily light-polluted, see https://www.lightpollutionmap.info https://www.lightpollutionmap.info . If OP happen to pass by a place with low light pollution, I encourage him/her to stay and watch the sky for a while (30 minutes ?) so that the eyes can adapt to darkness. It's really a neat experience.
- jakeogh 9y ago
  Mt. Graham, east of Tucson. Worth it. http://www.darksky.org/ http://www.darksky.org/

Sharlin 9y ago

It is a real shame that so many people don't recognize the Milky Way, by having lived their whole lives under light-polluted skies. But yes, even an optimally dark sky isn't that colorful to a human eye. That's because human low-light vision, provided by rod cells, is almost entirely monochromatic. A camera sensor doesn't have such limitations. You do need an exposure time of several seconds at least, but first and foremost you need to get away from light pollution. No amount of exposure time is going to help you inside a large city; the sky just comes up ugly orange-gray. To a totally dark-adapted human eye in an optimally dark location the night sky is a sight to behold.

Spellchamp 9y ago

Hello, not a direct reply to your questions but you'd be right to say that most photos you see of space are inaccurate for colour. We call them "false colour" images. Typically what you'll do is take images of the same object with a telescope at a variety of different wavelengths. The basic pattern is to use 3 images, and then use each one to represent a different colour from red, green and blue. Then layering one on top of another you can create an image that looks like the bright and colourful ones you typically see of nebula/pulsars etc. This way you get lots of detail, since different parts of the celestial bodies are only visible at certain wavelengths. So a single wavelength image would be over saturated with certain effects. So even though these are technically "false" colour images of space. There is a scientific reason for doing it. Not saying that the photo in the article is false, I think it's just had a long exposure time. Anyway, hope this helps understanding of astrophotography in general.

Angostura 9y ago

That's the milky way, though I'm sure that's not visible from anywhere in earth like that. Whenever I've seen it, it has been a band across the sky, not an arc. Perhaps a composite using a wide-angle lens? One of the other replies to your comments talks about false colour photography, however this one, I think is probably true colour with long exposure. The problem you have is that for very dim objects the colour-sensing 'cone' cells in your retina pretty bad. In low light conditions you're much more reliant on the rod cells, which are monochrome only (and more abundant in the periphery - if you are ever looking at a dim object, try looking at it from the corner of your eye).

eric_h 9y ago
> Whenever I've seen it, it has been a band across the sky, not an arc That photo is most certainly a composite of some sort. It was also taken in the Southern Hemisphere (Australia).