Daily Extra :
Astronomy & Space Word of The Day
refractive index (index of refraction): The ratio of the velocity of light in a vacuum to the velocity of light with in a material.
Today in History:
1966: Surveyor 2 - USA Lunar Soft Lander launched. Surveyor 2 failed and impacted the moon.
1970: Luna 16 - USSR Lunar Lander landed on the moon at Mare Fecunditaits located at latitude 0°41' S and longitude 56°18' E. 100 grams of lunar samples were returned to the Earth.