Transcript: 21 - 27 February, 2006

PAUL Welcome to Idaho Skies on Radio Boise. This is the second week of February. We’re your hosts, Paul..

RACHEL ...Rachel..

KRIS ...And Kris

PAUL This week the inner planet Mercury makes its appearance.

KRIS Last week Idaho Skies told you the path that the planets travel around the sun is low to the horizon on February mornings. Well, the opposite is true in the evening.

RACHEL The ecliptic rises steeply in the evening, which means planets in the west after sunset are much higher above the horizon.

KRIS Mercury is at its best this week. But that doesn't mean Mercury is as easy to see as Venus.

RACHEL Mercury orbits the sun at a distance of 36 million miles to the earth's distance of 93 million miles. Therefore Mercury never appears very far from the sun.

KRIS But you can find Mercury if you look low in the west at seven PM, or 30 minutes after sunset. Mercury will be the first star you can see.

PAUL And by low, we mean low. Mercury will only be nine degrees above the horizon.

RACHEL Nine degrees is about the angle your four fingers span when your arm is fully outstretched. So you'll need a clear western horizon to see Mercury.

PAUL Mercury is getting a visitor in 2011

KRIS The Messenger spacecraft is on its way to this mysterious planet.

RACHEL Mercury has only been visited by one spacecraft, the Mariner 10.

KRIS The Mariner 10 spacecraft discovered that Mercury looks a lot like the moon, with craters, impact basins, and smooth plains.

PAUL Since it's so close to the massive sun, Mercury's rotation is tidally locked to the sun.

RACHEL This means the planet rotates on its axis in sync with its revolutions around the sun.

KRIS For every orbit around the sun, Mercury only rotates one and a half times on its axis.

RACHEL If this were true on Earth, our days would last eight months. And with a day lasting eight months, a year would be a day and a half long.

KRIS The surface of Mercury is extremely hot. Day time temperatures can soar to a high of 870 degrees Fahrenheit.

PAUL That's hot enough to melt lead.

RACHEL But Mercury is not the hottest planet in the solar system. Because of its dense atmosphere, Venus has a slightly hotter surface temperature of 900 degrees.

PAUL Mariner 10 only photographed half of Mercury during its three passes of the planet in 1974 and 1975.

RACHEL To photograph Mercury, Mariner 10 was put into an orbit similar to Mercury

KRIS Since Mercury rotates in sync with its orbit, every time Mariner 10 passed Mercury, the same side of Mercury was facing the sun, so there was only one side we were able to see.

RACHEL The largest feature on Mercury recorded by Mariner 10 was the Caloris Basin. A huge impact site on the planet measuring 830 miles across. That's larger than Idaho, Washington, and Oregon combined.

KRIS In 2011 the Messenger spacecraft will go into orbit around Mercury, something Mariner 10 was unable to do. So who knows what kinds of features we'll discover on Mercury.

RACHEL That's Idaho Skies for the fourth week of February. Join us next month and hear about the astronomical events visible from Idaho. For Idaho Skies this is Rachel.

KRIS ...Kris..

PAUL ... and Paul.