Stars and Galaxies

 

Star size comparison

Stars

Stars are massive, bright balls of plasma held together by gravity. Stars vary in size and color (temperature). The study of stars is far beyond the scope of this humble web site, so I would refer you to Wikipedia for further reading or a star chart or sky map. (Links)

The methods of viewing stars are with the naked eye, with binoculars, using a small telescope, using a large telescope or by viewing images from the internet.

(Image courtesy of Dave Jarvis and made available under the Creative Commons Attribution 3.0 Unported license.)

(Click on the image on the left to view a larger version.)

The constellation Orion

Constellations

A constellation is a section of the night sky defined by exact boundaries. It also refers to the prominent stars within that boundary that form a pattern, for example, the constellation Orion. These patterns formed in the sky are a product of human perception, rather than the stars having any actual astrophysical relationship to each other.

There are 88 official constellations defined by boundaries by the International Astronomical Union (IAU).

The study of constellations is far beyond the scope of this humble website, so I would refer you to Wikipedia for further reading or a star chart or sky map. (Links)

The methods of viewing constellations are with the naked eye, with binoculars or by viewing images from the internet. Using a small or large telescope narrows the view too much to see the entire constellation.

(Image courtesy of Torsten Bronger and made available under the GNU Free Documentation License.)

(Click on the image on the left to view a larger version.)

The Crab Nebula

Nebulae

Nebula are generally divided into one of four types.

H II regions include diffuse nebulae, bright nebulae and reflection nebulae. These nebulae are generally composed of hydrogen and dust with no well defined boundaries. They are usually illuminated by stars near the nebula or within it. An example of a bright nebula is the Carina Nebula which has been used as the background for this website.

Planetary nebula are the gaseous shells ejected from low-mass giant stars when they transform and become white dwarfs. An example is the Cat's Eye Nebula.

Supernova remnants result when a high-mass star reaches its life's end and collapses on itself. The expanding shell of gas forms a supernova remnant. An example is the Crab Nebula pictured to the left.

Dark nebulae are seen as dark clouds blocking the light of objects behind it. An example is the Horsehead Nebula.

The study of nebulae is far beyond the scope of this humble website, so I would refer you to Wikipedia for further reading or a star chart or sky map. (Links)

The methods of viewing nebulae are by using a large telescope or by viewing images from the internet. Nebulae generally are too distant and faint to see with the naked eye, with binoculars or a small telescope.

(Click on the image on the left to view a larger version.)

A spiral galaxy

A barred spiral galaxy

An elliptical galaxy

Galaxies

A galaxy is a massive system, gravitationally bound, consisting of stars, stellar remnants, gas, dust and "dark matter". Galaxies can contain as few as 10 million stars up to one trillion stars (a million million). It is estimated that there are at least 100 billion galaxies in the observable universe. Galaxies can range in size from 3,000 to 325,000 light years in diameter.

Our own Milky Way Galaxy is believed to be a barred spiral galaxy about 100,000 light years in diameter containing between 100 billion to 400 billion stars.

The study of galaxies is far beyond the scope of this humble website, so I would refer you to Wikipedia for further reading or a star chart or sky map. (Links)

The images at left are of a spiral galaxy, a barred spiral galaxy and an elliptical galaxy.

The methods of viewing galaxies are by using a large telescope or by viewing images from the internet. Galaxies generally are too distant to see with the naked eye, with binoculars or a small telescope.