Stars are classified into groups based on their apparent color.  The color tells us informaiton about the surface temperature of the star.

The standard classes are (temperatures are in Kelvin):

• O – Blue Stars: > 30,000 K
• B – Blue-White Stars: 10,000 – 30,000 K
• A – White Stars: 7,500 – 10,000 K
• F – Yellow-White Stars: 6,000 – 7,500 K
• G – Yellow Stars: 5,200-6,000 K
• K – Orange Stars: 3,700 – 5,200 K
• M – Red Stars: 2,400 – 3,700 K

Additional Classes:

• L – Sub-Red Dwarf Stars:  1,300 – 2,400 K
• T – Brown Dwarf Stars: 700 – 1,300 K
• Y – Sub-Brown Dwarf Stars: < 700 K

The Sun is a G2V star.  The class is G – a Yellow Dwarf Star.  2 is its Subclass (they range from 0 to 9 with 0 being the hottest.  The V i the sun’s Spectral Type and it tells us that the sun in on the Main Sequence.