Navigation by Pulsar

On the golden record that accompanies the Voyager spacecraft, there is a map showing the location of Earth.  It’s not a road map that you might pull out when navigating a city, but a 3D map showing the location of a star, the Sun, in a populous galaxy.  But just how would this map work? And more importantly, what are the map markers? If you notice the lines at the bottom left of the golden record image, they all intersect at a common center point.  This is the Sun, and the lines extend out showing relative distances to the nearest...

Leap Second: Why June 30th, 2015 Will be a Long Day

I presume that you know what a leap year is.  A year is the amount of time the Earth takes to orbit the Sun, and is measured as 365 days, or 365 rotations of Earth.  It is, in reality, a little bit longer.  Each orbit of the Sun takes 365.25 days, or 365 days and six hours.  So what do we do with that six hours? We ignore it for 3 years.  On the fourth year we add up those extra hours and we get 24 hours, an extra day! So we add in February 29th every four years. This...