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Hawk xSx
2010-Dec-13, 10:09 PM
I know that the images taken are extremely high quality and the effort would be enormous.

But maybe my understanding of Speed of Light and photography of deep sky objects are incorrect. Why is it that when we see a Collapsing Star, we only see a "snapshot" or a moment in time. How is not happening in real-time by the time it gets to us?

Hornblower
2010-Dec-13, 11:30 PM
I know that the images taken are extremely high quality and the effort would be enormous.

But maybe my understanding of Speed of Light and photography of deep sky objects are incorrect. Why is it that when we see a Collapsing Star, we only see a "snapshot" or a moment in time. How is not happening in real-time by the time it gets to us?

A "collapsing star" could be:

1. A supernova, which will run its course in a short time, which we can observe in its entirety. If we could observe one up close, we could make a movie of it.

2. A beginning protostar, which could take thousands or millions of years to run its course. Anything we could observe in a human lifetime would be a snapshot by comparison.

Are you referring to one of these examples, or something else entirely?

How does the speed of light figure in this?

slang
2010-Dec-13, 11:48 PM
Welcome to BAUT, Hawk xSx


I know that the images taken are extremely high quality and the effort would be enormous.

But maybe my understanding of Speed of Light and photography of deep sky objects are incorrect. Why is it that when we see a Collapsing Star, we only see a "snapshot" or a moment in time. How is not happening in real-time by the time it gets to us?

Exposure time. It's the same with a normal photocamera. If you leave it on automatic settings, it will open the shutter longer, the darker it gets. Objects in "deep space" are very faint, you can't see them with the naked eye. To take an image with a telescope, the camera behind it needs a lot of time to capture enough light to show the very far objects. Much more than say the 1/25th of a second that a movie frame takes. For example, the famous Hubble Ultra Deep Field (http://hubblesite.org/newscenter/archive/releases/2004/07/) took 11.3 days of exposure... Have a look through the Astrophotography section of this forum, most people posting images there also say how long it took to take that picture.

Hawk xSx
2010-Dec-13, 11:54 PM
It was a generalized example of something that would have a lot of motion with it's distance from us. I just wonder why "movies" or "slideshows" aren't put together for us to see celestial moments as we get them?

Disregard the speed of light mention, I had it wrong and can't explain it. I am also having a hard time explaining myself. It's just hard finding the terminology to express what I'm asking.

WayneFrancis
2010-Dec-14, 06:58 AM
To expand on the great explanation slang gave. Even though a picture might take 11.3 days to take that is just a blip in cosmic time scales. Very distant objects are also VERY BIG objects. IE The amount of stuff that happens in 11 days or even a few years is nothing. What would a super nova event look like in another near by galaxy? Just a bright pin point light. We wouldn't see a cloud or anything. The resolution is just to small.

Lets put this into perspective with something many people have seen. The crab nebula. While the initial super nova happened very quickly and a bright spot appeared in the sky telescopes wouldn't have seen much more then a bright spot for a long time. It happened almost 1,000 years ago is about 11 light years in diameter. So to a movie of the super nova, which would just look like a bright point of light pretty much, to what we see now would take 1,000 years.

Even now it is still expanding at 1,500km/sec but if we took a picture every day for a year and made a 24 frame/sec 15 second movie you wouldn't notice any real change to it.

Jeff Root
2010-Dec-14, 12:46 PM
Whenever there is something moving or changing in the sky,
and NASA or anyone else is able get pictures of it, those pictures
are sequenced into movies, and put on the Internet by whoever
made them. I've seen movies of comets, asteroids, Jupiter's
rotation, the stars moving across the sky in a single night, and
several others. But there are very, very few things outside the
Solar System that change rapidly enough to be easily visible
over a period of less than centuries, that also make interesting
movies.

You can find animations online made from eight HST images
of the variable star V838 Monocerotis, showing an intense
pulse of light from the star reflecting from successive shells
of dust that the star gave off thousands of years earlier.

-- Jeff, in Minneapolis

Peter B
2010-Dec-14, 01:36 PM
There's another issue which might be relevant, depending on exactly what your concerns are: viewing time is valuable, and there's a lot to look at. It's rarely possible for a given telescope to keep pointing at an object of interest often enough to get images you could put together into a movie. It's different for spacecraft, though. It can be very interesting, for example, to put together a sequence of images from, say, Cassini making a close approach to a moon of Saturn. But that's something happening over the course of a few hours at most.

JustAFriend
2010-Dec-14, 10:16 PM
You could certainly spend a couple of thousand years (OK, maybe at the very least a few hundred) taking photos of the same object and building it into an animation.

Remember that photography has only been around for 150years and there's a LOT of stuff we just haven't been around long enough to see yet.

Even for the short-lived stuff remember that its only been the last few decades that we've had orbiting observatories and before that you could only take a few hours exposure each night IF the weather and the atmosphere cooperated. It ain't easy to get those pretty pictures.

eburacum45
2010-Dec-15, 12:02 AM
Here's the V838 Monocerotis animation Jeff Root mentioned
http://observatory.open.ac.uk/data_store/fun_stuff/v838_monocerotis.html
here's one of Hubble's Variable Nebula
http://www.umanitoba.ca/science/astronomy/cbrown/imaging/hvn/hvnanimation.html
Here's one of the phases of Venus
http://apod.nasa.gov/apod/ap060110.html
and one of Jupiter
http://www.flickr.com/photos/brownpau/2531256238/
and one of the Moon
http://apod.nasa.gov/apod/ap010218.html

most astronomical phenomena aren't fast enough to make good movies, but there are quite a few that are.

slang
2010-Dec-15, 12:44 AM
Just to avoid possible misunderstandings: the movies and animations in the last posts, although beautiful, are not real-time movies, as I think Hawk xSx meant. They are still long(ish) exposures, with varying amounts of time between them, stitched together to make a sped up movie. Real-time video only works with closer subjects, such as the Moon, from orbit. The Japanese moon orbiter Kaguya (AKA SELENE) (http://en.wikipedia.org/wiki/SELENE) carried two HDTV cameras.

Hawk xSx
2010-Dec-16, 11:33 PM
Right. I was asking specifically for real-time movies. But now I understand it much better. It's been something lingering and finally have a good grasp on it now. Thank you.

Jeff Root
2010-Dec-17, 09:23 AM
For objects which are far away from Earth but close to the
camera, such as Mars, Jupiter, and Saturn, the limiting factor
is usually the speed at which the images can be transmitted.
That in turn is limited by the amount of power available for
the transmitter and the size of the reflector dishes (if any) on
the transmitting and receiving antennae. A really powerful
transmitter on Mars, sending through an antenna able to
concentrate the signal into a narrow beam, could send real-
time video to Earth delayed only by the light travel time.

-- Jeff, in Minneapolis