- #1
- 344
- 0
How accurate is it possible to measure the EM spectre ?
FrankPlanck said:It depends on your tool...
russ_watters said:You're asking about the red and blue shift of stars and galaxies? Very accurately, since you have spectral absorption lines to compare with a reference.
Bjarne said:What about absorbed photons, is it only these that has very certain frequencies that are absorbed?
For example here http://www.astro.ucla.edu/~wright/doppler.htm is mentioned that those at 393 nm are absorbed.
My question is; - how accurate is that?
Is it only these that have the exact wavelength 393nm that are absorbed
What when one is 394 nm or 392nm , - will noting happen ?
If so it must be possible to measure much more accurate as 0.1% to 1%.
I mean the difference between 393nm and 392 nm is not much.
Bjarne said:What about absorbed photons, is it only these that has very certain frequencies that are absorbed?
For example here http://www.astro.ucla.edu/~wright/doppler.htm is mentioned that those at 393 nm are absorbed.
My question is; - how accurate is that?
Is it only these that have the exact wavelength 393nm that are absorbed
What when one is 394 nm or 392nm , - will noting happen ?
If so it must be possible to measure much more accurate as 0.1% to 1%.
I mean the difference between 393nm and 392 nm is not much.
Drakkith said:...spectrographs are looking at light that was emitted from an object. The spectral lines are absorbed at the SOURCE, not the instrument.
This would imply a velocity of ~1/400c or about 1000km/s, which is equivalent to a rotational period of about an hour for a sun-sized star. As comparison: The sun's surface needs 25-30 days for a rotation (depends on the latitude), and 1/400c is much more than the escape velocity of stars.Drakkith said:The light that is at 392 nm is NOT being absorbed by calcium, the line is wider than 1 nm because of several different effects, such as the rotation of the star.