This is planetary radio. The student astronauts are coming from all over Earth to explore Mars.

Hi everyone, I'm Matt Kaplan.

This week on planetary radio, we'll visit with the Los Angeles couple that opened the door

for a young South African girl to join this very select group. We'll also hear the words of that 15-year-old student.

Bruce Betts has news of a Lunar Eclipse along with a new trivia contest, and Emily has

the low-down on longitude and latitude all around the solar system.

Here's the first half of her report.

Hi, I'm Emily Loch Duwala with questions and answers.

A listener asked, what are the criteria for assigning the locations of longitudes and latitudes on bodies other than Earth.

The definition of latitude on other planetary bodies is pretty simple.

Due to the process by which the solar system formed,

every single body in the solar system rotates about a spin axis.

A plane perpendicular to the spin axis that passes through the body's center of mass

defines the equator, or zero degrees latitude.

So even potato-shaped bodies like asteroids and the smallest moons have an equator and therefore latitude.

The end of the spin axis that points to the north of the plane of the solar system

is the north pole of the body or 90

degrees positive latitude and the end of the spin axis that points to the south

is the south pole or 90 degrees negative latitude.

Londitude is much more arbitrary.

There are 360 degrees of longitude and longitude has to be measured from some reference point on the rotating body.

On Earth, of course, longitude is defined with reference to the Prime Meridian, which passes through a point at the Royal Observatory in Greenwich, England.

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