One light-year is the distance light travels in one year. The speed of light is about 300,000 km/s . How far is 1 light-year?
A) 1.08 billion km (1,080,000,000, or 1.08 109 km)
B) 300 thousand km (300,000, or 3 105 km)
C) 9.46 trillion km (9,460,000,000,000, or 9.46 1012 km)
D) 18 million km (18,000,000, or 1.8 107 km)
Question 2
What eventually halts the gravitational collapse of an interstellar gas cloud that forms an object that is massive enough to become a star?
A) the central object becoming hot enough to sustain nuclear fusion in its core
B) a critical fraction of the gas has been driven further into space
C) nothing; all collapsing gas clouds become black holes
D) the crowding of electrons in the core
Species richness decreases with distance from the source pool.
Muskox populations remain in the Arctic all year, though they migrate to higher elevations in the wi
The carbon cycle. Numbers are storage as 1015 g or fluxes as 1015 g per year (data from Schlesinger
Evidence that Light Travels at a Finite Speed
A light shield over an optical sensor being installed before the rotor is attached.
Events in human fertilization. The light micrograph shows a fertilized human oocyte.