- Binary Stars
- They are pairs of stars moving in orbit around their common centre of mass. They are also known as double stars. An optical pair appears to be double because two stars lie in the viewer’s line of vision. Examples of double stars are Phakt in Columba and Arcus in Crux.
- Black Dwarf
- It is the remains of a dead white dwarf star after its heat is radiated into space.
- Black Hole
- It is what remains of a super collapsed star, whose gravitational pull is so great that no light can escape.
- Brown Dwarf
- It is a star whose mass is too small to have fusion occur at its core because the temperature and pressure there are too insufficient. It is also not very luminous.
- Galaxy
- It is a system of stars, dust, and gas held together by gravity. There are three basic types: spiral, elliptical, and irregular.
- A spiral galaxy is a flattened, discus-shaped collection of stars, having a central bulge. Examples include the Milky Way and Andromeda.
- An elliptical galaxy ranges in shape from a sphere to a flattened globe. Examples include the Sagittarius Dwarf and M31.
- An irregular galaxy has no pattern of shape. Examples include the Large Magellanic Cloud and the Small Magellanic Cloud.
- Main-Sequence Stars
- It is an ordinary star, one of about 90% of the stars that can be seen from Earth. It is much smaller than a giant star. It burns hydrogen into helium through nuclear fusion within itself. An example is our Sun.
- Nebula
- It is a cloud of gas or dust, and is considered to be the birthplace of a new star. There are three basic types: emission, reflection, and dark.
- An emission nebula glows brightly because its gas is energized by the stars formed within it. An example is the Orion Nebula.
- A reflection nebula is one in which sunlight reflects off the grains of dust within it. An example is the one which surrounds stars of the Pleides cluster.
- A dark nebula is a dense cloud of molecular hydrogen which absorbs light behind it. Examples are the Horsehead Nebula in Sagittarius and the Crab Nebula in Taurus.
- Neutron Star
- It is the tiniest star, having collapsed into a superdense state. It is thought to have formed when a large star exploded as a supernova.
- Nova
- It is a star that brightens suddenly, lasts a few days, fades away, and returns to its normal state.
- Pulsar
- It is a rapidly spinning neutron star that emits pulses of energy.
- Quasar
- It is a quasistellar object, very far away and very bright. It gives off more energy than one hundred giant galaxies.
- Red Giant
- It is a large, bright star, many times larger than the Sun, but with a cool surface. It is believed to be in the end stage of its life cycle. Examples are Aldebaran in Taurus and Ras Algethi in Hercules.
- Star Colours
- They are, in descending order of temperature, greenish, blue, blue-white, yellowish-white, yellow, orange-yellow, orange-red, red, infrared.
- Supergiant
- It is the largest and most luminous type of star, being a dying star. It has used up its hydrogen fuel and has begun to expand and cool. Examples are Antares in Scorpius and Betelgeuse in Orion.
- Supernova
- It is an exploding supergiant, being the death of a star. The Crab Nebula was formed by a supernova.
- Variable Star
- It is a star whose brightness changes. This is usually caused by pulsations within it. Examples of variable stars are Polaris in Ursa Minor (Cepheid) and R Centauri in Centaurus (Mira).
- White Dwarf
- It is a very dense, small, hot star in the last stage of its life. It occurs when a red giant sheds its outer layers as a planetary nebula. The electrons and protons have been packed as closely as possible by gravity. An example of the white dwarf is the Pup, companion star of Sirius in Canis major.
- Wolf-Rayet Star
- It is a hot, luminous star that is rapidly losing mass in a wind. It represents a late stage in the life of massive stars.
For added information see Astronomy Expert, an external link.
