Expert: Tom Whiting - 12/16/2007

Question
hi,
  how are auroras formed? , what is a solar spectrum? why do stars twinkle? and why does some stars have more brightness than other stars?
thanks for the help


Answer
Hi Monisha,
Aurora, or northern lights, are created when high energy
charged particles come in from the sun, then our magnetosphere surrounding the earth directs these particles to the magnetic poles where they stike our atmosphere very high up, like 60-100 miles high...causing the very thin air up there to fluoresce, or glow, like a neon light bulb. So they are mostly visible from the far northern latitudes.
The solar spectrum...astronomers take the light of the sun
and pass it through a prism (like a raindrop does to form
a rainbow), or a specific lined grating (does the same thing) to produce the color spectrum from red to violet.
Since the white light of the sun is composed of all colors,
astronomers are speading the light out into it's individual
colors according to wavelength.  If highly magnified, you
can see lines in this spectrum, and those lines represent
the individual elements present in the light (sun) so astronomers can determine not only what elements are present but also the relative amounts of each element, since each element has it's own "fingerprint" on the spectrum.  Each element emits it's own wavelength of light,
and we can determine this wavelength using the solar spectrum.

Stars twinkle simply because we have an atmosphere.  If we
had no atmosphere, stars would always remain steady, unchanging pinpoints of light.  IN FACT, anytime you see
something out of the ordinary...haloes around the sun or moon, orange red sunsets, orange yellow moonrises, flattened suns at the horizon, sun pillars, mock suns,
twinkling stars, blobby stars, wavering moonlight or sunlight, anything different in the sky from "normal"....
that's all our atmosphere doing it, including twinkling of
the stars.  We live at the bottom of a "swimming pool" called our atmosphere; anyone swimming on top, like the jet stream or high thin clouds, disturbs the air, so we see
this disturbance as the effects mentioned above.

Stars are like light bulbs...we have bright mercury vapor
lights, we have little Christmas tree bulbs...some are close to us, some are far away. Stars are exactly the same
way....some are huge giants, some are little dwarf stars;
some are very close (relatively speaking) and some are very
far away.  So each star has it's individual brightness depending on both it's size (internal brightness) and distance...it's a combination of both factors, just like different light bulbs seen at....different distances.
Hope all this helps,
Clear Skies,
Tom Whiting
Erie, PA