- NASA’s Viking 1 lander first showed humans what a sunset looked like on Mars in 1976. Several more Red Planet robots have since sent back a variety of views of Martian sunrises and sunsets.
- Real number (Wikipedia)
In mathematics, a real number is a number that can be used to measure a continuous one-dimensional quantity such as a distance, duration or temperature. Here, continuous means that pairs of values can have arbitrarily small differences. Every real number can be almost uniquely represented by an infinite decimal expansion.