- #1
- 344
- 0
How accurate is it possible to measure the EM spectre ?
It depends on your tool...
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.
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.
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.
...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.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.