3 ms·

The thing that surprises me is how stationary everything in space seems to be, in order for this to have been possible. But everything is moving, right? So how

The thing that surprises me is how stationary everything in space seems to be, in order for this to have been possible. But everything is moving, right? So how could a series of pictures over this long of a time work out to be so clear?

simcop2387 6y ago
a combination of things, the distances you're looking at are mind-numbingly huge. you might think it's a long way to the chemist but that's just peanuts to space. This means that even though things are moving, and fast, they still look like they're in the same place from this far away. Along with that, the images aren't a single exposure over years, but days at a time at worst. that means that any minor movement can be adjusted for when combining the images for the final result.
portaljester 6y ago
The sensor gathering the light moves to compensate for Earth's rotation.
dnadler 6y ago
Because the distances involved are truly massive. 5 years is nothing at these scales
atombender 6y ago
Camera systems like these use computerized tracking to account for the rotation of the earth. The earth rotates really fast! The earth is also orbiting the sun pretty fast, but it's my understanding (I'm not an expert) that you don't need to account for error here, since the Orion nebula is so far away. Think about how the sun stays in the same place in the sky even as you're driving fast on the highway. The nebula is unimaginably far away compared to the sun, and relative movement between the earth, the solar system, and Orion are all undetectable at these scales. I've read that even the Hubble telescope doesn't need to account for parallax error for such far-away objects during long exposures, which can last up to 20 minutes. Maybe someone here on HN can do (or point to) the math for us.
_xerces_ 6y ago
The seeming lack of movement even convinced the Greeks that the Earth is stationary: https://www.lesswrong.com/posts/noBKApHwFm8aMuvnw/link-the-greek-heliocentric-theory https://www.lesswrong.com/posts/noBKApHwFm8aMuvnw/link-the-g...
- stjohnswarts 6y ago
  *some greeks. You can't fool Aristarchus though.
db48x 6y ago
It's an illusion. The Earth is rotating, but it's easy to compensate for that so that the stars don't turn into streaks. You just mount the telescope and camera on a motorized mount that turns slowly to counteract the rotation of the Earth. That's cheap and easy to do, so everyone does it unless they specifically want to show off the rotation of the Earth. Every star in that image has some proper motion, usually dozens or hundreds of km/s, and there's no way to counteract that. For any single exposure that's not large enough velocity to turn the stars into a streak, but it is enough for the stars to be in different positions relative to each other from year to year. Since different panels of the image were captured in different years, the overlaps between those panels won't match perfectly. When stitching the panels together, the photographer will probably have edited the photograph so that each star is taken from only one panel. That will prevent any stars from being cut in half or blurred together from both panels, but there could be stars that moved fast enough to have crossed the boundary between the panels and they could show up in the full image twice. Good luck spotting them though. The Earth is also moving around the Sun, so there is an additional apparent motion, but it's smaller in magnitude to than the proper motion and won't cause any extra problems. The gas clouds are also moving. Some of them are expanding, some of them are being pushed by stellar winds, etc. Stars can form in dense clouds, and then the stellar wind from the new star pushes all the remaining dust away to create a bubble. You can see these motions over the course of years, so presumably they caused some minor mismatches between panels that were photographed at different times. Since these features are fuzzy, it's not hard to blend neighboring panels together even when they're taken years apart. https://www.youtube.com/watch?v=ofCooIkIwvQ https://www.youtube.com/watch?v=ofCooIkIwvQ is a great explanation with good visuals, and it has photographs taken by the New Horizons probe that directly show stellar parallax when compared with photographs taken at the same time from Earth. Even that is only visible on the nearest stars; none of the other stars in those photographs were close enough to move at all.

simcop2387 6y ago

a combination of things, the distances you're looking at are mind-numbingly huge. you might think it's a long way to the chemist but that's just peanuts to space. This means that even though things are moving, and fast, they still look like they're in the same place from this far away. Along with that, the images aren't a single exposure over years, but days at a time at worst. that means that any minor movement can be adjusted for when combining the images for the final result.

portaljester 6y ago

The sensor gathering the light moves to compensate for Earth's rotation.

dnadler 6y ago

Because the distances involved are truly massive. 5 years is nothing at these scales

atombender 6y ago

Camera systems like these use computerized tracking to account for the rotation of the earth. The earth rotates really fast! The earth is also orbiting the sun pretty fast, but it's my understanding (I'm not an expert) that you don't need to account for error here, since the Orion nebula is so far away. Think about how the sun stays in the same place in the sky even as you're driving fast on the highway. The nebula is unimaginably far away compared to the sun, and relative movement between the earth, the solar system, and Orion are all undetectable at these scales. I've read that even the Hubble telescope doesn't need to account for parallax error for such far-away objects during long exposures, which can last up to 20 minutes. Maybe someone here on HN can do (or point to) the math for us.

_xerces_ 6y ago

The seeming lack of movement even convinced the Greeks that the Earth is stationary: https://www.lesswrong.com/posts/noBKApHwFm8aMuvnw/link-the-greek-heliocentric-theory https://www.lesswrong.com/posts/noBKApHwFm8aMuvnw/link-the-g...

stjohnswarts 6y ago
*some greeks. You can't fool Aristarchus though.

db48x 6y ago

It's an illusion. The Earth is rotating, but it's easy to compensate for that so that the stars don't turn into streaks. You just mount the telescope and camera on a motorized mount that turns slowly to counteract the rotation of the Earth. That's cheap and easy to do, so everyone does it unless they specifically want to show off the rotation of the Earth. Every star in that image has some proper motion, usually dozens or hundreds of km/s, and there's no way to counteract that. For any single exposure that's not large enough velocity to turn the stars into a streak, but it is enough for the stars to be in different positions relative to each other from year to year. Since different panels of the image were captured in different years, the overlaps between those panels won't match perfectly. When stitching the panels together, the photographer will probably have edited the photograph so that each star is taken from only one panel. That will prevent any stars from being cut in half or blurred together from both panels, but there could be stars that moved fast enough to have crossed the boundary between the panels and they could show up in the full image twice. Good luck spotting them though. The Earth is also moving around the Sun, so there is an additional apparent motion, but it's smaller in magnitude to than the proper motion and won't cause any extra problems. The gas clouds are also moving. Some of them are expanding, some of them are being pushed by stellar winds, etc. Stars can form in dense clouds, and then the stellar wind from the new star pushes all the remaining dust away to create a bubble. You can see these motions over the course of years, so presumably they caused some minor mismatches between panels that were photographed at different times. Since these features are fuzzy, it's not hard to blend neighboring panels together even when they're taken years apart. https://www.youtube.com/watch?v=ofCooIkIwvQ https://www.youtube.com/watch?v=ofCooIkIwvQ is a great explanation with good visuals, and it has photographs taken by the New Horizons probe that directly show stellar parallax when compared with photographs taken at the same time from Earth. Even that is only visible on the nearest stars; none of the other stars in those photographs were close enough to move at all.