-A collection of stars and dust held togegther by gravity
-Found throughout the universe
-Vary greatly in size and shape
Groups of stars that are held together by gravity and travel together, they range from 10 stars to 1 million.
-A collection of 50 to 1000 stars
-Appear along the main band of the Milky Way
-A collection of 100 000 to 1 million stars arranged in a distinctive spherical shape
-Appear around the centre of the Milky Way
-A group of 40 galaxies including the Milky Way
-The diameter is about 10 million light-years
-Andromeda and the Milky Way are the largest galaxies in the local group
A supercluster is a gigantic cluster of 4-25 clusters of galaxies which are hundreds of millions of light-years away
Shapes of galaxies
There are 3 different types of galaxies, elliptical (long, football shaped, largest type of galaxy), spiral (pin-wheel or whirlpool shaped, has arms with central bulge), irregular shaped galaxy (oddly shaped)
Cosmology is the study of the universe. Cosmologists try to answer questions such as; how did the universe begin? Is it changing? Using technology cosmologists have been able top see backwards in time to almost the very beginning of the universe.
Hubble noticed when looking at the spectra of galaxies the spectral lines were slightly displaced, known as the Doppler effect. This phenomenon occurs in the pitch of an ambulance as it approaches or moves away. As the ambulance moves toward you the sound waves are compressed resulting in a higher frequency. Light waves behave in a similar way.
Longer wavelengths are associated with the red end of the spectrum. Since the wavelength of light from an object moving away from an observer is lengthened toward the red end of the visible spectrum it is said that the spectrum is redshifted
The wavelength of light from an object moving toward an observer is shortened toward the blue end it is said that the spectrum of the object is blueshifted.
Some time in the distant past, the universe was very compact, small, and dense. The universe began expansion about 14 billion years ago.
Cosmic Microwave Background (CMB) Radiation
Wilson and Penzias from Bell telephone labs were looking for some source of "noise" that could interfere with satellite communications. They accidentally discovered the microwave noise that was produced by radiation left over from the big bang. The temperature of the CMB radiation was about -270oC
-The missing mass of galaxies
-The most abundant form of matter in the universe
-Invisible to telescopes
-It is only detectable by the effect it causes
-It makes up 23% of the universe
-Scientists predict that after the big bang the expansion of the universe should be slowing down due to gravity
-But dark energy overcame gravity and is accelerating the expansion of the universe