Scale of Distance to Closest Stars

4.2 Light Years away

Voyager with the speed 60,000 km/hour (17km/s) will take 80000 years to get there

http://www.khanacademy.org/video/scale-of-distance-to-closest-stars?playlist=Cosmology+and+Astronomy

Solar "wind": electrons and protons (400km/s)

Black Holes

http://www.khanacademy.org/video/black-holes?playlist=Cosmology+and+Astronomy

white dwarf
neutron star
singularities (infinite mass density)
event horizon

Scale of Earth and Sun

http://www.khanacademy.org/video/scale-of-earth-and--sun?playlist=Cosmology+and+Astronomy

Speed of a bullet : 280 m/s (1000 km/hour, ~speed of jet) will take 40 hours to go around the earth
Sun 109x circumference of earth (half a year to go around the Sun)
AU - Astronomical Unit = 150,000,000 km away from the earth (take 17 years to get to the sun from the earth)

Scale of Solar System

http://www.khanacademy.org/video/scale-of-solar-system?playlist=Cosmology+and+Astronomy

Scale of Small

From honey bees to cells, virus, and atoms -- understanding the scale of the very small

http://www.khanacademy.org/video/scale-of-the-small?playlist=Cosmology+and+Astronomy