Expert: Tom Whiting - 2/22/2008

Question
1. how does an atom produce a photon of light and what causes these photons to vary for any particular single element of the Periodic Chart?

2.  What happens when the diameter of the telescope "objective" is changed?

3. What are the advantages to orbital telescopes?

I have been struggling to find the answers to these questions.  If you can help me out, it would really be appreciated.  

Answer
Hi Jonesha,
 The easiest explanation...all atoms, the electrons going around
them, the electrons' orbit have different "energy levels" in the
different 'shells' around the nucleus.  So when an electron, generally the outermost electron,  is 'excited' by say, an incoming packet of energy (say a UV or gamma ray photon), it absorbs that energy by being bumped up into a higher orbit....read that, a higher energy level, then it almost immediately decays (read that-- drops back down into a lower energy level), and in the process, emits a photon of light with a specific wavelength of that energy drop.
And each electron orbit and each element, has it's own specific
energy drop.  (It HAS to lose that energy to drop back down into a lower energy state or lower orbit) and in the process, we see it losing that energy as a photon of light that it emits, which our spectroscopes detect. And each element gives off a different wavelength of colored photon, because there are thousands of different energy level differences. Just like there are thousands of specific colors in the spectrum of light.  (If there wasn't, then our system here wouldn't work)!

So that's why an excited hydrogen atom gives off a specific red light photon, sodium a specific yellow light photon, copper green, cobalt blue, and so on. It's simply the electrons 'jumping around'
their orbits, and each element, AND each isotope of each element,
gives off a different wavelength (color) of photon.
And of course, millions of atoms of that particular element are doing this all at the same time, and continuously as long as the incoming energy is available.
That's basically how it works, and how we can identify which element,
and even how much of each element, is present.

2.  By increasing the aperture...read that, double the size of a
mirror, since mirror area goes up by the square as Area = pi radius- squared for area, you bring in 4 times more light, thus you can
see dimmer and dimmer objects.  If you upgrade from a 3 inch mirror
to a 6 inch mirror telescope, then your area has gone from 3 squared
to 6 squared, or from 9 to 36 - a 4 times increase. (We can avoid
including the value of Pi (3.1416) because we are simply making
a comparison here, an so we can disregard Pi as it's in each comparison if you want to compute the actual area). To double again
from a 6" mirror, and you go to a 12" mirror, then 12 squared is
144, which again is four times more area than a 6" mirror at 36.
So you can observe even dimmer objects.
So that's why a 3 inch telescope is good down to about 11.8 magnitude stars, a 6 inch is good down to 13.6 magnitude, and a 12
inch is good down to about 14.6 magnitude stars. (It's a reverse
scale, that magnitude....the higher the number, the dimmer the object. And it's a logarithmic scale, not linear.  
So by increasing the area of the mirror, you get to see dimmer and
dimmer (read that- more distant, in most cases) objects. That's why
astronomers always want BIGGER and BIGGER telescopes! To see dimmer
and dimmer (read that- even more distant) objects in the night sky.

3. We on the surface live at the bottom of a 'swimming pool' our
atmosphere.  If someone is swimming at the top, like high altitude
winds or the Jet Stream, OR there is dust and water vapor blocking
our view, then our view of the night sky is not the best. Things like
that interfere with our views.  By placing telescopes in orbit, in
space above our atmosphere, then they avoid all those problems.
It's called 'resolution'...or sharpness of the object being viewed.
All Earthbound telescopes are limited in resolution by our atmosphere, but an orbiting telescope in space, is not limited in
resolution. (sharpness).  So that's the big advantage there. And,
obviously, it's well worth it...that's why we put them there.

Another factor, for UV, X-ray, and Gamma ray scopes, those wavelengths of light don't make it down to the Earth's surface. (Some
Ultraviolet makes it thru, for sunburns, but it's not very much
compared to the total incoming UV radiation). So all those types of scopes HAVE to be up in orbit, because they just wouldn't work on the surface of the Earth due to our atmosphere interfering...stopping
that light from reaching the surface.

Hope all this helps,
Clear Skies,
Tom Whiting
Erie, PA