Idaho skies Transcript for September 30th to October 2nd

PAUL

Welcome to Idaho Skies for September 30^th and October 1^st and 2^nd. We’re your hosts, Paul…

RACHEL

…and Rachel.

PAUL

Don’t forget to look for Mercury in the morning this weekend.

RACHEL

It’s already reached its highest distance above the horizon…

PAUL

…and is rapidly approaching the horizon again.

RACHEL

To see Mercury, go outside at about 6:30 AM.

PAUL

And look for a star very low in the east.

RACHEL

The star is bright enough that you’ll have no trouble finding it.

PAUL

The only problem might be is having a horizon too high for Mercury to clear before sunrise.

RACHEL

Did you know that a year on Mercury only lasts for 88 Earth days?

PAUL

And a day last 58 Earth days?

RACHEL

Mercury also has a much more elliptically shape orbit than Earth.

PAUL

Its elliptical orbit means the orbital speed of the planet changes more dramatically than it does for Earth.

RACHEL

By traveling faster as it approaches the sun…

PAUL

…and slower as it travels away from the sun.

RACHEL

Combining its changing orbital speed and rotational rate means the sun doesn’t travel neatly from one horizon to the other as it does on Earth.

PAUL

In fact, the sun actually moves backwards across the sky for part of a Mercurian day.

RACHEL

Before 1974, astronomers thought that Mercury’s day lasted as long as its year.

PAUL

This is called being tidally locked and it happens to astronomical bodies orbiting close to their parent.

RACHEL

In the case of Mercury, its year lasts 1.5 days and perhaps in the future, the day and year will come into sync.

PAUL

That’s Idaho Skies for the 30^th, 31^st of September and the 1^st of October.

RACHEL

Be sure to follow us on Twitter at Idaho Skies for this week’s event reminders and sky maps.

For Idaho Skies this is Rachel…

PAUL

…and Paul.

RACHEL

Dark skies and bright stars.