Idaho Skies Transcript for February 11th and 12th

RACHEL
Welcome to Idaho Skies for February 11th and 12th. We’re your hosts, Rachel...

PAUL
...and Paul.

RACHEL
Hey, the moon reaches first quarter phase today.

PAUL
At first quarter, only the eastern half of the moon is visible. That’s because sunlight is also illuminating half of the moon’s farside. The boundary between day and night is called the moon’s terminator. It’s where sunrise is occurring on the moon. Since the sun is just rising along the terminator, shadows are especially long there. That makes it easier to see craters and mountains that reside along the terminator. 

RACHEL
The moon has a near and far side because its day lasts 29 Earth days, the same time it takes for the moon to orbit Earth. Astronomers use the term tidally locked to describe this situation. Small moons are normally tidally locked to their host planet when the moons are close to the planet. Because it’s tidally locked, the lunar farside was luna incognita until the beginning of the Space Age. 

PAUL
Once spacecraft began imaging the lunar farside, we discovered that it was very different from the near side. While the near side has lots of craters, maria, and mountain ranges, the farside is just battered with craters. The farside contains only 3% as much lunar maria as the near side. So why, astronomers have wondered, is the lunar farside so different than the near? One clue was the discovery that the crust on the farside is much thicker than the near side.

RACHEL
Perhaps a thicker crust makes it more difficult for subsurface magma to work its way to the surface and erupt as lava to create lunar maria. But why is the crust thicker here? One hypothesis is that left over material from the moon’s origin fell back on the lunar farside as a pancake of material. Another is that the still hot Earth prevented the moon’s near side from cooling down as quickly as the farside. 

PAUL
That’s Idaho Skies for the 11th and 12th of February.

RACHEL
Be sure to read our blog for additional information. It’s at idahoskies.blogspot.com

For Idaho Skies this is Rachel...

PAUL
...and Paul.

RACHEL
Dark skies and bright stars.