This chart illustrates the variation in available solar power for each of
NASA's twin Mars Exploration Rovers over the course of approximately two
Mars years. Two factors affect the amount of available power: the tilt of
Mars' axis and the eccentricity of the Mars' orbit about the sun.
The horizontal scale is the number of Martian days (sols) after the Jan.
4, 2004, (Universal Time) landing of Spirit at Mars' Gusev Crater. The
vertical scale on the right indicates the amount of available solar power
as a ratio of the amount available at the equator when Mars is closest to
the sun (perihelion). The red line indicates power availability at
Spirit's landing site (Gusev). The blue line indicates power availability
at Opportunity's landing site (Meridiani).
The vertical scale on the right applies to the dotted line, indicating the
latitude north or south of Mars' equator where the noon sun is overhead at
different times of the Martian year.
