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View Full Version : I have a question (pulled from "If it turns out BBT is wrong...)



westernjoe
2007-Oct-20, 04:36 AM
Hope no one minds too much that I post this here, but I hated to start a new thread and waste too much time....but I'm looking for a bit of wisdom....
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Let me say up front that I know nothing about astronomy, so please excuse me if this question seems ridiculous. But I've been having an argument with a friend about something. The premise is if there is someone standing on the sun (hypothetically, of course) and there is another person on the earth with a high-powered telescope.....and if the person on the sun is doing jumping jacks -- would the person on the earth peering through the high-powered telescope be able to see the person's movements on the sun in real time...or would they be delayed.

I have gone round and round with my friend, he says there would be a delay, and although he may be right I don't understand why....and the reasoning makes no sense to me. Thanks for any explanation.

Van Rijn
2007-Oct-20, 07:51 AM
Hope no one minds too much that I post this here, but I hated to start a new thread and waste too much time....but I'm looking for a bit of wisdom....
------

Let me say up front that I know nothing about astronomy, so please excuse me if this question seems ridiculous. But I've been having an argument with a friend about something. The premise is if there is someone standing on the sun (hypothetically, of course) and there is another person on the earth with a high-powered telescope.....and if the person on the sun is doing jumping jacks -- would the person on the earth peering through the high-powered telescope be able to see the person's movements on the sun in real time...or would they be delayed.

I have gone round and round with my friend, he says there would be a delay, and although he may be right I don't understand why....and the reasoning makes no sense to me. Thanks for any explanation.

Welcome to BAUT. Don't worry about starting a new thread for a question like this - it's more likely people will see it that way, and it isn't appropriate for this thread. Anyway, I suspect a moderator will move your post to Q&A sooner or later. As for your question: The speed of light is such that we don't normally notice the delay for events on Earth, but it takes time for the light of any event to reach your eyes, even for somebody doing jumping jacks in the same room with you. "Real time" just means the time delay is too short for our slow brains to notice. At its distance, it takes a bit over eight minutes for the light from the sun to reach the Earth.

Neverfly
2007-Oct-20, 05:37 PM
So a little over an 8 minute delay.

Since the sun is 149,597,871 km from earth;

And light travels at a wee bit less than 300,000 km per second.

Meanwhile, if I was standing on the sun, I'd be hopping and jumping something fierce too!

01101001
2007-Oct-20, 05:52 PM
Even with the man hopping on the moon, just 384000 kilometers, about 1.3 lightseconds, distant, and communicating via radio, his words took over a second between starting to leave his lips and starting to arrive at our ears. If we could see him through a telescope, there would be a similar lag to his movement. It would not be an evident lag, but everything would be seen 1 second after it happened there.

Wikipedia: Speed of light (http://en.wikipedia.org/wiki/Speed_of_light):


Another consequence of the finite speed of light is that communications with spacecraft are not instantaneous, and the gap becomes more noticeable as distances increase. This delay was significant for communications between Houston ground control and Apollo 8 when it became the first spacecraft to orbit the Moon: For every question, Houston had to wait nearly 3 seconds for the answer to arrive, even when the astronauts replied immediately.