Monday, March 16, 2015

Astro FOTD

Velocity in km/s is numerically nearly equal to its value in parsecs/megayear. (1 km/s = 1.04 pc/Myr)

Fact is handy for navigation, as well as for things like realizing that a constant Hubble parameter of 70 km/(s Mpc) implies an age of 14 Gyears for the Cosmos. (Hubble parameter isn't really constant, but current value is close to the mean).

The fastest moving bodies in the solar system (say a long period comet at the moment of solar impact) travel at about 600 km/s, and the nearest stars are less than 2 parsecs away. At that speed, the trip would take roughly 1/300 of a Myr, or 3300 years.

Hey, it beats driving.