Question about stars????????

Question

Why are red giants so bright even thought they are cool stars?

Why are white dwarfs so dim even though the have high temperatures?

Answer 1

To answer your first question here, a red giant star is relatively cool, around 2,500 to 3500 degrees F, but very luminous because of its great size! All normal stars are expected to pass eventually through a red-giant phase as a consequence of their stellar evolution.
As a star, like our Sun lets say, uses up its hydrogen by converting it to helium, its central core contracts while the outer layers expand and cool. This process produces the low temperature and large size (from 10 to 1,500 times that of the sun) that is typical of the red giant stars.
Although most giant stars are red in color, some prominent giant stars are colors near the red end of the spectrum.
For example, there is Arcturus which is (orange); Aldebaran which is (orange), and Capella which is a (yellow) color.
And to answer your last question, as to why white dwarf stars are so dim, even though they have high temperatures(around 10,000K), the answer has to do with mass and the size(diameter) of the star!
Now since hot things like stars are usually quite bright, we can ask just how white dwarfs would be any different? The answer is because they are also very small and therefore very dense as well!!!
As a matter of fact, they are so dense, that they are made up mainly of electron-degenerate matter, which means that the pressure inside the white dwarf does not respond to an increase in temperature in the usual way.
This causes white dwarfs to have the odd property that if their mass increases their radius decreases! And it is this tremendously 'squeezed' matter that helps give the white dwarf star its extremely high temperature, and small diameter!!!

Answer 2

Red giant stars have an immense surface area from which their light comes while white dwarf stars have a surface area only about as large as Earth.

If you want to see some cool graphics showing the size difference between different kinds of stars check out this website ==>http://www.co-intelligence.org/newsletter/comparisons.html

Answer 3

Are they? That's a good question. Size would be my guess. Not only size, but mass. Red giants are fairly young stars, so they've got more burning, only not quite as intensely. White dwarfs have lost quite a bit of mass going through the various stages, and so they're not burning as much. And of course, bigger things are easier to see.

Answer 4

The surface area of a star is what's important here; a Giant star has far more surface from which photons can be released, versus a dwarf star, with as little as 1/10,000,000th the area.

Answer 5

The answer is right there in your question. We're talking about red *giants* and white *dwarfs*.

Answer 6

Red Giants are....Giants...they are huge and give off a lot of energy. A white dwarf may be hot but it is a...Dwarf...meaning it is small.

Answer 7

To make it clearer, red giants are really big, which makes them brighter (luminosity is partly a function of size). And white dwarfs are obviously relatively small, which makes them dimmer.