RACHEL
Welcome to Idaho Skies for December 5th and 6th. We’re your hosts, Rachel...
PAUL
...and Paul.
RACHEL
We mentioned last time that Mercury and Venus are visible together in the morning sky.
PAUL
Both Venus and Mercury are what astronomers call inferior planets. This means both orbit the sun in paths that are wholly inside Earth’s orbit. This means they experience a greater gravitational attraction to the sun than Earth. Therefore, they orbit the sun more quickly than Earth does. Since one orbit of the sun is a year, the length of the year for Mercury and Venus is shorter than Earth’s.
RACHEL
The length of a year on Mercury is 88 days. In other words, an Earth year lasts just over four Mercurian years and Mercury will celebrate the passing of another year on March 3rd. The length of a year for Venus is longer at 225 days. That makes a Venusian year only 62% as long as a terrestrial year. Venus will celebrate the passing of another year on July 18th.
PAUL
Mercury is a world that looks much like our moon. The planet’s diameter is 3,032 miles, or 38% the diameter of Earth and 142% the diameter of the moon. What atmosphere Mercury has is called an exosphere. Exospheres consist of molecules that are gravitational bound to a planet but so thinly spread out that they seldom ever collide with one another. The result is that the air pressure in an exosphere is essentially unmeasureably low.
RACHEL
Spacecraft and Earth-based telescopes have detected hydrogen, helium, oxygen, sodium, and potassium in Mercury’s exosphere. The hydrogen and helium almost certainly originate with the sun’s solar wind. The oxygen, sodium and potassium likely originate in the planet’s crust. They are released from Mercury the action of solar heat and wind.
PAUL
That’s Idaho Skies for the 5th and 6th of December.
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.
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