Hello,
I want to know how they measured the distance between the Earth and the moon. I'v done some search work, they used a laser beam and a mirror. But my question is, did they used the Doppler effect or not? And maybe someone can lead me to a site where they explain the Doppler effect, Like the know the distance between Earth and Exoplanets.
Thanks in advance,
The distance between the Earth and the Moon was measured by Dr. Bay Zoltán in 6 February, 1946. He was a Hungarian scientist, by the way. They used a radar beam, not a laser, but the concept is the same. And no, it didn't involve the Doppler-effect. They shot the beam and waited for it to return... measuring the time meanwhile. And given the speed of the beam (c, the speed of light), a simple multiplication gave them the result. A very nice experiment.
Here is his brief cv:
http://en.wikipedia.org/wiki/Doppler_effect
And here is an article about the Doppler-effect:
http://en.wikipedia.org/wiki/Zoltan_Bay ^ Are you sure? That seems like a highly improbably way to conduct such an experiment.
Okay, but i wanted to know about the laser not the first 1 who did it, It was something with mirrors set by Apollo. But they didn't used Doppler then?
The laser target was one of the experiments taken to the moon by Armstrong + Aldrin (Apollo 11).
The distance has been monitored at Jodrell Bank Cheshire since then.
| Teezgaff wrote: |
The laser target was one of the experiments taken to the moon by Armstrong + Aldrin (Apollo 11).
The distance has been monitored at Jodrell Bank Cheshire since then. |
Correct.
Basically the put a "mirror" on the moon and shoot it with a laser.
Side note, the moon is moving away from us.The Doppler effect would not be used to measure distance; it is used to measure relative speed. (Such as in a police officer's radar gun.)
All the details you might want can be found here.[url]
http://science.nasa.gov/headlines/y2004/21jul_llr.htm[/url]
| Quote: |
Here's how it works: A laser pulse shoots out of a telescope on Earth, crosses the Earth-moon divide, and hits the array. Because the mirrors are "corner-cube reflectors," they send the pulse straight back where it came from. "It's like hitting a ball into the corner of a squash court," explains Alley. Back on Earth, telescopes intercept the returning pulse--"usually just a single photon," he marvels.
The round-trip travel time pinpoints the moon's distance with staggering precision: better than a few centimeters out of 385,000 km, typically. |
| HoboPelican wrote: |
All the details you might want can be found here.[url]
http://science.nasa.gov/headlines/y2004/21jul_llr.htm[/url]
| Quote: | Here's how it works: A laser pulse shoots out of a telescope on Earth, crosses the Earth-moon divide, and hits the array. Because the mirrors are "corner-cube reflectors," they send the pulse straight back where it came from. "It's like hitting a ball into the corner of a squash court," explains Alley. Back on Earth, telescopes intercept the returning pulse--"usually just a single photon," he marvels.
The round-trip travel time pinpoints the moon's distance with staggering precision: better than a few centimeters out of 385,000 km, typically. |
|
Okay, i've already used that site, thanks anyway, it is like someone said here, Doppler is for speed. But I once read an article they used Doppler for finding exoplanets, however i lost that article. :s | Marston wrote: |
| ^ Are you sure? That seems like a highly improbably way to conduct such an experiment. |
Yes, I am quite sure; I am a Hungarian engineer also. I have learned of his experiment. And if you look around, you will find more improbable stuff being done. So, don't underestimate Hungarian scientists!
| Jurado wrote: |
| Okay, but i wanted to know about the laser not the first 1 who did it, It was something with mirrors set by Apollo. But they didn't used Doppler then? |
-->
| ocalhoun wrote: |
| The Doppler effect would not be used to measure distance; it is used to measure relative speed. (Such as in a police officer's radar gun.) |
Exactly; thank you.
| Jurado wrote: |
| HoboPelican wrote: | All the details you might want can be found here.[url]
http://science.nasa.gov/headlines/y2004/21jul_llr.htm[/url]
| Quote: | Here's how it works: A laser pulse shoots out of a telescope on Earth, crosses the Earth-moon divide, and hits the array. Because the mirrors are "corner-cube reflectors," they send the pulse straight back where it came from. "It's like hitting a ball into the corner of a squash court," explains Alley. Back on Earth, telescopes intercept the returning pulse--"usually just a single photon," he marvels.
The round-trip travel time pinpoints the moon's distance with staggering precision: better than a few centimeters out of 385,000 km, typically. |
|
Okay, i've already used that site, thanks anyway, it is like someone said here, Doppler is for speed. But I once read an article they used Doppler for finding exoplanets, however i lost that article. :s |
Exoplanets have a very slow movement compared to Earth; still, it can be detected by the Dopler effect. (Their radial movement at least.) But this is not the case with the Moon; it has too much radial movement to measure the distance. But, on a rough approximate, it worked then. | Jurado wrote: |
Okay, i've already used that site, thanks anyway, it is like someone said here, Doppler is for speed. But I once read an article they used Doppler for finding exoplanets, however i lost that article. :s |
Yes, doppler can be used in that application - basically the doppler shift is used to detect a periodic shift in the spectrum of a star which indicates a large planet orbiting the star. As far as I remember the technique is only good for detecting very large planets.
Regards
Chris
