Light from a star reaches Earth through the process of electromagnetic radiation. The light energy travels through space in the form of waves, and when it reaches Earth, it can be seen by the human eye.
While brightness refers to how much light we see from a star, luminosity is the total amount of light that a star emits. Luminosity takes into account the star's size, temperature, and distance from Earth, while brightness only considers its apparent brightness from our viewpoint.
The temperature of a star is directly related to its color. The hotter the star's surface, the shorter the wavelengths of light it emits, resulting in a bluer color. Cooler stars have longer wavelengths of light and appear redder in color.
There are various methods for measuring the distance to a star, including parallax, spectroscopic parallax, and the cosmic distance ladder. Parallax involves measuring the apparent shift in a star's position as the Earth orbits the Sun. Spectroscopic parallax uses the star's spectrum to determine its distance. The cosmic distance ladder combines various techniques to estimate distances to stars and other celestial objects.
Yes, we can see light from stars that have died because it takes time for the light to travel from the star to Earth. So even though the star may have died, its light is still visible to us until it reaches Earth. This means that when we look at the night sky, we are seeing a combination of light from both living and dead stars.