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 define star brightness in terms of apparent magnitude (how bright the star appears from Earth) and absolute magnitude (how bright the star appears at a standard distance of 32.6 light years, or 10 parsecs). Astronomers also measure luminosity — the amount of energy (light) that a star emits from its surface.
Spectroscopy — the use of light from a distant object to work out the object is made of — could be the single-most powerful tool astronomers use, says Professor Fred Watson from the Australian Astronomical Observatory.
“You take the light from a star, planet or galaxy and pass it through a spectroscope, which is a bit like a prism letting you split the light into its component colours.
“It lets you see the chemicals being absorbed or emitted by the light source. From this you can work out all sorts of things,” says Watson.
Stars are enormous spheres of ignited gas that light the cosmos, and seed it with the materials for rocky worlds and living beings. They come in many different types and sizes, from smouldering white dwarfs to blazing red giants.
Stars are often classified according to spectral type. Although they emit all colors of light, spectral classification considers only the peak of this emission as an indicator of the star’s surface temperature. Using this system, blue stars are the hottest, and are called O-type. The coolest stars are red and are called M-type. In order of increasing temperature, the spectral classes are M (red), K (orange), G (yellow), F (yellow-white), A (white), B (blue-white), O (blue).
What Are The Different Types of Stars?
There are three main types of telescopes to choose from:
Each of these has it’s own advantages and disadvantages. I’ve explained the differences between these types of telescopes below.