tens to thousands of young stars                   individual stars                   easily seen or verified that they exist (resolved)                  Pleiades in the constellation Taurus

        Globular Clusters
 

Old stars               contain 100,000 to 1,000,000 stars,               High density in the center               individual stars from earth-based telescopes difficult to see               appear as a "glob" of light               Globular Cluster M15 see from Earth

 

    Binary Stars
        Double stars
 

Kepler's laws                       elliptical orbit                       are on opposite sides of the center of mass.

 
        The Sirius Binary System
 

Main sequence(Sirius A) and a white dwarf companion (Sirius B).                           orbits are drawn to scale, but not the sizes                           Sirius A is considerably larger than the Sun                           white dwarf Sirius B is about the size of the Earth    animation (scroll down)

 

Galaxies
        Spiral Galaxies

presence of gas in the disk                   stars still forming                   low density galactic field                   labeled Sa-d,m

        Barred Spiral

developed bar in the interior region of the spiral arms                SBa-d,m

 
        Elliptical

categories E0-7               depending on their degree of ellipticity               uniform luminosity               similar to the bulge in a spiral galaxy, with no disk               stars -old and - no gas             in the high density field,               at the centre of clusters.

 

    Irregular

small galaxies          labeled Irr          no bulge          an ill-defined shape.          The Magellenic clouds