WHAT'S UP: Temperatures around the solar system

Apr 22, 2011


What about the moon?  It must be cold on the moon.  It is cold on the moon, on the night side, where the sun isn’t visible.  The average temperature of the night side of the moon is about -150C, which is almost 140 degrees below zero Fahrenheit.  But on the day side of the moon, the temperature climbs over 100C, which is about 212F.

The average temperature on the moon is only slightly lower than on Earth, but since the moon lacks a blanketing atmosphere, the temperature there swings wildly between day and night.

Also, the moon spins very slowly compared to Earth.  A solar day on the moon is about a month long, so at any given mid-latitude location, the sun is above the horizon warming the environment for about two weeks, then, it is below the horizon for the next two weeks, during which everything cools down.

What about Mercury, the planet closest to the sun?  It’s got to be hot on Mercury.  It is hot on Mercury, on the day side, where the sun is above the horizon.  The average temperature of the day side of Mercury is perhaps as high as 500C, or about nearly 1,000F.  But on the night side of Mercury, the temperature sinks to -170C or so, which is about 280F below zero.

The temperature swing between day and night on Mercury is extreme because like the moon, Mercury does not have a warming, moderating atmosphere.

Venus, on the other hand, is more like Earth than the moon or Mercury.  Venus has a thick atmosphere composed mainly of carbon dioxide, one of the so-called “greenhouse gasses.”

Venus is only about 30 percent closer to the sun than is Earth.

The surface temperature on Venus is a nearly uniform 460C, or about 850F, day and night.

Venus exemplifies the important roll carbon dioxide plays in setting a planet’s overall temperature.

Other temperatures around the solar system today: the temperature on Pluto is about -233C, or almost 400 degrees below zero Fahrenheit, the temperature of the surface of the sun is about 6,000C, or nearly 11,000F.

The hot spot in the solar system is the core of the sun, where the nuclear reactions fusing hydrogen into helium take place.  Here, the temperature is a searing 15,000,000C, or 27,000,000F.  Temperatures like this lose their meaning in everyday context.

By the way, to convert between the Celsius and Fahrenheit temperature scales approximately, double the temperature in Celsius and add 30 to get the temperature in Fahrenheit.  To go the other way, subtract 30 from the temperature in Fahrenheit and divide by 2 to get the temperature in Celsius.

The Fahrenheit scale is the official temperature scale in only two countries: the United States and Belize.  Nearly everyone on Earth uses the Celsius scale to tell temperature.

On the Fahrenheit scale, water freezes at 32F and boils at 212F; on the Celsius scale, water freezes at 0C and boils at 100C.

No matter what scale you use to tell temperature, though, it has been a cold spring in West Michigan.

— By Doug Furton, a member of the physics faculty at GVSU.  Send questions and suggestions to dgf@inbox.com.  An archive of some of his “What’s up” columns is available online at http://gegenschein.wordpress.com.



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