Blue And Red Flashing Star In Sky

The stars’ temperatures make them look red or blue in the sky. A star emits energy across the electromagnetic spectrum. The spectral energy of a star is a measure of the amount of energy it emits at a wavelength. Blue stars are hotter, while red stars are cooler; this is called black-body radiation.

Black body radiation

Black body radiation is the emission of energy from a body at all wavelengths. The spectral energy distribution (SED) of a star is a plot of the spectral energy at each wavelength. Blue stars have a higher spectral energy at shorter wavelengths, while red stars have a lower spectral energy at shorter wavelengths.

This is also the concept of how blacksmiths are able to tell if a piece of metal is hot enough to shape. The metal piece glows red and then glows brighter the hotter it gets. 

Black body radiation wavelength

Stars and the Earth’s Surface

How we view a star is also determined by the earth’s surface. When a star’s light enters the atmosphere and bounces around inside, it scatters the wavelength of light throughout the earth, causing changes in color and also twinkling. This process is called scintillation. 

The earth’s atmosphere has a lot of moving gases, making it dense; light inconsistently passes through the surface, which results in stars appearing to change color. This is especially true for the sun. 

The color of the sun changes depending on the angle at which we look at it. The most common example is during sunrise and sunset. The sun’s color appears to be different at sunrise and sunset because, during those times, the sun is lower in the sky and must pass through more of Earth’s atmosphere, diffusing the radiation more.

Is the sun the hottest star?

The sun is a hot star, but not the hottest. The sun’s surface temperature (the photosphere) ranges about 4,000 – 6,000°K (6,700 – 11,000 °F). The hottest star that we know of is called WR 102, and it has a surface temperature of 210,000 °K (377,540 °F). Even though WR 102 is way hotter than the sun, it doesn’t impact the earth.

The reason why WR 102 doesn’t affect us is that it’s so far away. It’s about 9,500 light-years from Earth, which is about 55.8 quadrillion miles. Additionally, it’s also half the size of the sun. So even though it’s the hottest star, its distance and size make it harmless to us.