c by starlight

BillyJoe · 8th February 2003, 03:17 AM

How can the speed of light be measured using the light from a distant star?

(You could obviously use starlight like any other source of light to measure the speed of light in the ususal way but this method uses starlight specifically.)

Dub · 8th February 2003, 05:07 AM

c is only the speed of light in a vaccum. As most of space is a vaccum star light would be a good source to use. Although im not sure how its done.

BillyJoe · 8th February 2003, 06:14 PM

Quote:

Originally posted by Dub
c is only the speed of light in a vaccum.

Okay, there will be a slight error due to the Earth's atmosphere and gravity.

Quote:

Originally posted by Dub
As most of space is a vaccum star light would be a good source to use. Although im not sure how its done.

Do you want a clue?

8th February 2003, 08:12 PM

Doesn't relate to gravitational pertebution, I guess? Maybe some weird thing with pulsars, and looking at the redshift...nah. I've got no idea. I suppose just having two stations on earth with atomic clocks and lasers or photon sensors isn't right either?

BillyJoe · 9th February 2003, 01:22 AM

Quote:

Originally posted by rwald
....gravitational pertebution?.....Maybe some weird thing with pulsars, and looking at the redshift?..... two stations on earth with atomic clocks and lasers or photon sensors?

None of those, at least not the method I'm looking for.

Want a clue?

Skeptoid · 9th February 2003, 02:26 AM

Is this the method you have in mind? Lifted from discovery.com.

Quote:

[ B]ritish astronomer James Bradley ... obtained a very good estimate for the speed of light. Since the speed of light is finite, starlight falling on the Earth will exhibit a slight angular displacement depending on the direction the Earth is moving (in its orbit). Bradley knew the orbital speed of the Earth to be approximately 30 kilometers per second, roughly 1/10,000 of the known value of the speed of light. By measuring, at different points in the Earth's orbit, the angular displacement of starlight falling from a given star Bradley was able to estimate the speed of light to within 1 percent of the currently accepted value.

BillyJoe · 9th February 2003, 03:57 AM

****, Skeptoid, you weren't supposed to go googling to find the answer

.
Perhaps you can redeem yourself by explaining the "angular displacement" bit

.

BillyJoe · 9th February 2003, 03:59 AM

.....and no googling.

Skeptoid · 9th February 2003, 12:30 PM

Without googling, huh? Let's see ... The angular displacement is what astronomers call the aberration of light. It is the apparent shift in position of a star due to Earth's motion around the sun. It is roughly the ratio of the Earth's speed to c. Thus, if one knows the angular displacement and the Earth's speed, one can estimate c. An astronomer has to adjust his telescope to compensate for the angular displacement in much the same way as a person tilts his umbrella forward when walking through the rain.

Best I can do from memory. Please correct me if I'm in error.

BillyJoe · 10th February 2003, 02:04 AM

Sounds good.

Here's another analogy...
A sailboat has the wind coming in straight over the beam. The flag at the top of the mast is flying at right angles to the boat indicating the true direction of the wind. However, as the boat sails forward, the wind seems to shift towards the direction in which the boat is heading. The faster the boat travels, the greater the shift. Of course, to set his sails, the sailor uses the apparent direction of the wind not the true direction of the wind (just as the astronomer sets his telescope towards the apparent position of the star)

I'm a bit surprised this thread didn't create more interest. Oh well.

xouper · 11th February 2004, 11:47 AM

bump

Skeptical Greg · 11th February 2004, 12:11 PM

Quote:

Originally posted by BillyJoe

I'm a bit surprised this thread didn't create more interest. Oh well.

Interest?!!!

Darn, I was just preparing a paper on this ( which I thought was very original material )....

At least you have saved me a lot of trouble... Thanks..

BillyJoe · 12th February 2004, 02:10 AM

Obviously the best thread on the forum.....I'm still getting thanks for it after twelve months!

8th February 2003, 03:17 AM	#1
BillyJoe Penultimate Amazing Join Date: Aug 2001 Location: MOOROOLBARK Posts: 12,539	c by starlight How can the speed of light be measured using the light from a distant star? (You could obviously use starlight like any other source of light to measure the speed of light in the ususal way but this method uses starlight specifically.)
	__________________ A secular society is one in which no one loses any liberty as a consequence of someone else's religious beliefs. NB Allowing yourself to get led around the nose by a person like Craig is a losing strategy. SH Morality is a social coating around a Darwinian core. JC My joke about freewill: There is no basis for it.

8th February 2003, 05:07 AM	#2
Dub Thinker Join Date: Nov 2001 Posts: 247	c is only the speed of light in a vaccum. As most of space is a vaccum star light would be a good source to use. Although im not sure how its done.
Dub Thinker Join Date: Nov 2001 Posts: 247	__________________ "Men occasionally stumble over the truth, but most of them pick themselves up and hurry off as if nothing ever happened." Sir Winston Churchill "Faith is the great cop-out, the great excuse to evade the need to think and evaluate evidence. Faith is belief in spite of, even perhaps because of, the lack of evidence." Richard Dawkins "Our ignorance is God; what we know is science." Robert Ingersoll "The meme for blind faith secures its own perpetuation by the simple unconscious expedient of discouraging rational inquiry." Richard Dawkins "Paranormal phenomena have a habit of going away whenever they are tested under rigorous conditions. This is why the $1 million reward of James Randi is safe." Richard Dawkins

8th February 2003, 06:14 PM	#3
BillyJoe Penultimate Amazing Join Date: Aug 2001 Location: MOOROOLBARK Posts: 12,539	Quote: Originally posted by Dub c is only the speed of light in a vaccum. Okay, there will be a slight error due to the Earth's atmosphere and gravity. Quote: Originally posted by Dub *As most of space is a vaccum star light would be a good source to use. Although im not sure how* its done.** Do you want a clue?
	__________________ A secular society is one in which no one loses any liberty as a consequence of someone else's religious beliefs. NB Allowing yourself to get led around the nose by a person like Craig is a losing strategy. SH Morality is a social coating around a Darwinian core. JC My joke about freewill: There is no basis for it.

8th February 2003, 08:12 PM	#4
rwald Guest Posts: n/a	Doesn't relate to gravitational pertebution, I guess? Maybe some weird thing with pulsars, and looking at the redshift...nah. I've got no idea. I suppose just having two stations on earth with atomic clocks and lasers or photon sensors isn't right either?
rwald Guest Posts: n/a

9th February 2003, 01:22 AM	#5
BillyJoe Penultimate Amazing Join Date: Aug 2001 Location: MOOROOLBARK Posts: 12,539	Quote: Originally posted by rwald ....gravitational pertebution?.....Maybe some weird thing with pulsars, and looking at the redshift?..... two stations on earth with atomic clocks and lasers or photon sensors? None of those, at least not the method I'm looking for. Want a clue?
	__________________ A secular society is one in which no one loses any liberty as a consequence of someone else's religious beliefs. NB Allowing yourself to get led around the nose by a person like Craig is a losing strategy. SH Morality is a social coating around a Darwinian core. JC My joke about freewill: There is no basis for it.

9th February 2003, 02:26 AM	#6
Skeptoid Graduate Poster Join Date: Sep 2002 Posts: 1,532	Is this the method you have in mind? Lifted from discovery.com. Quote: [ B]ritish astronomer James Bradley ... obtained a very good estimate for the speed of light. Since the speed of light is finite, starlight falling on the Earth will exhibit a slight angular displacement depending on the direction the Earth is moving (in its orbit). Bradley knew the orbital speed of the Earth to be approximately 30 kilometers per second, roughly 1/10,000 of the known value of the speed of light. By measuring, at different points in the Earth's orbit, the angular displacement of starlight falling from a given star Bradley was able to estimate the speed of light to within 1 percent of the currently accepted value.

9th February 2003, 03:57 AM	#7
BillyJoe Penultimate Amazing Join Date: Aug 2001 Location: MOOROOLBARK Posts: 12,539	****, Skeptoid, you weren't supposed to go googling to find the answer . Perhaps you can redeem yourself by explaining the "angular displacement" bit .
	__________________ A secular society is one in which no one loses any liberty as a consequence of someone else's religious beliefs. NB Allowing yourself to get led around the nose by a person like Craig is a losing strategy. SH Morality is a social coating around a Darwinian core. JC My joke about freewill: There is no basis for it.

9th February 2003, 03:59 AM	#8
BillyJoe Penultimate Amazing Join Date: Aug 2001 Location: MOOROOLBARK Posts: 12,539	.....and no googling.
	__________________ A secular society is one in which no one loses any liberty as a consequence of someone else's religious beliefs. NB Allowing yourself to get led around the nose by a person like Craig is a losing strategy. SH Morality is a social coating around a Darwinian core. JC My joke about freewill: There is no basis for it.

9th February 2003, 12:30 PM	#9
Skeptoid Graduate Poster Join Date: Sep 2002 Posts: 1,532	Without googling, huh? Let's see ... The angular displacement is what astronomers call the aberration of light. It is the apparent shift in position of a star due to Earth's motion around the sun. It is roughly the ratio of the Earth's speed to c. Thus, if one knows the angular displacement and the Earth's speed, one can estimate c. An astronomer has to adjust his telescope to compensate for the angular displacement in much the same way as a person tilts his umbrella forward when walking through the rain. Best I can do from memory. Please correct me if I'm in error.

10th February 2003, 02:04 AM	#10
BillyJoe Penultimate Amazing Join Date: Aug 2001 Location: MOOROOLBARK Posts: 12,539	Sounds good. Here's another analogy... A sailboat has the wind coming in straight over the beam. The flag at the top of the mast is flying at right angles to the boat indicating the true direction of the wind. However, as the boat sails forward, the wind seems to shift towards the direction in which the boat is heading. The faster the boat travels, the greater the shift. Of course, to set his sails, the sailor uses the apparent direction of the wind not the true direction of the wind (just as the astronomer sets his telescope towards the apparent position of the star) I'm a bit surprised this thread didn't create more interest. Oh well.
	__________________ A secular society is one in which no one loses any liberty as a consequence of someone else's religious beliefs. NB Allowing yourself to get led around the nose by a person like Craig is a losing strategy. SH Morality is a social coating around a Darwinian core. JC My joke about freewill: There is no basis for it.

11th February 2004, 11:47 AM	#11
xouper Banned Join Date: Jan 2002 Posts: 2,189	bump
xouper Banned Join Date: Jan 2002 Posts: 2,189

11th February 2004, 12:11 PM	#12
Skeptical Greg Agave Wine Connoisseur Join Date: Jul 2002 Location: Just past 'Resume Speed' Posts: 12,872	Quote: Originally posted by BillyJoe I'm a bit surprised this thread didn't create more interest. Oh well. Interest?!!! Darn, I was just preparing a paper on this ( which I thought was very original material ).... At least you have saved me a lot of trouble... Thanks..
	__________________ " Somewhere between Jesus dying on the cross, and a giant bunny hiding eggs,there seems to be a gap in information. " Stan - Southpark Prove your computer is not a wimp ! Join the JREF Folders ! Team 13232

12th February 2004, 02:10 AM	#13
BillyJoe Penultimate Amazing Join Date: Aug 2001 Location: MOOROOLBARK Posts: 12,539	Obviously the best thread on the forum.....I'm still getting thanks for it after twelve months!
	__________________ A secular society is one in which no one loses any liberty as a consequence of someone else's religious beliefs. NB Allowing yourself to get led around the nose by a person like Craig is a losing strategy. SH Morality is a social coating around a Darwinian core. JC My joke about freewill: There is no basis for it.