You can tell the temperature of the star. Red stars are the coolest. Yellow stars are hotter than red stars. White stars are hotter than red and yellow.

A glance at the night sky above Earth shows that some stars are much brighter than others. However, the brightness of a star depends on its composition and how far it is from the planet. Astronomers also measure luminosity — the amount of energy (light) that a star emits from its surface.

The Luminosity of a star depends on BOTH its temperature and its radius (surface area): L is proportional to R2 T4. A hotter star is more luminous than a cooler one of the same radius. A bigger star is more luminous than a smaller one of the same temperature.

We measure the brightness of these stars using the magnitude scale. The magnitude scale seems a little backwards. The lower the number, the brighter the object is; and the higher the number, the dimmer it is. This scale is logarithmic and set so that every 5 steps up equals a 100 times decrease in brightness.

As the size of a star increases, luminosity increases. If you think about it, a larger star has more surface area. That increased surface area allows more light and energy to be given off. Temperature also affects a star’s luminosity.

Stars emit colors of many different wavelengths, but the wavelength of light where a star’s emission is concentrated is related to the star’s temperature – the hotter the star, the more blue it is; the cooler the star, the more red it is.

Blue stars tend to be the brightest, and red stars the dimmest. Apart from the temperature and brightness, the colour also usually —with the same qualification— indicates the size of a star: the hottest and most energetic blue stars are usually bigger and the red ones smaller.

Spica

Stars have different colors, which are indicators of temperature. The hottest stars tend to appear blue or blue-white, whereas the coolest stars are red.

All stars are white because they emit all wavelengths. Having said that their temperatures mean that they will have a bluer or redder tint, so their spectral class will be red, orange, yellow, yellow-white, white blue-white and blue (Classes M (orC&S), K, G, F, A, B & O).

The dead star, called a white dwarf, can be seen at the center of the image as a white dot….

As stars age, they run out of hydrogen to burn, decreasing the amount of energy they emit. Thus, younger stars can appear bluer while older ones appear more red, and in this way, a star’s color can tell us something about that star’s age.

The stars with the longest lifetimes are red dwarfs; some may be nearly as old as the universe itself.

1) The bigger a star is, the longer it will live. 2) The smaller a star is, the longer it will live. A smaller star has less fuel, but its rate of fusion is not as fast. Therefore, smaller stars live longer than larger stars because their rate of fuel consumption is not as rapid.

Stars live different lengths of time, depending on how big they are. A star like our sun lives for about 10 billion years, while a star which weighs 20 times as much lives only 10 million years, about a thousandth as long. Stars begin their lives as dense clouds of gas and dust.

White dwarfs are the hot, dense remnants of long-dead stars. They are the stellar cores left behind after a star has exhausted its fuel supply and blown its bulk of gas and dust into space.

After a star dies, there is still some residual heat left over. That heat makes the star (white dwarf or neutron star) glow, even though it is not producing any energy. Eventually, the star cools off and does indeed simply become a hunk of ash, which we call a “black dwarf.”

A: It’s rare, but stars do collide in the densest parts of our galaxy: near the center and in massive globular star clusters. In star clusters, the stars are moving relatively slowly, and so the “fender bender” results in the two stars merging into one new, more massive star that we call a blue straggler.

Most stars take millions of years to die. When a star like the Sun has burned all of its hydrogen fuel, it expands to become a red giant. After puffing off its outer layers, the star collapses to form a very dense white dwarf. …