Only A Little Star

We start with a poem about the Sun written by my wife Sherry.
“You’re only a little star!
(The Sun, the Sun)
You’re not too close,
Not too far.
(The Sun, the Sun)
You make me warm all over,
You light up my way,
You keep everything alive
As you shine on us each day.
How can you do so much
When you are
Only a little star?”
According to the Natural Sciences 102 course website at the University of
Arizona, a planet which can support life needs to have the following
characteristics: 1. “Orbit a star that remains stable in output for billions of years;
2. Be at a distance from the star so that its surface water is liquid, not frozen; 3.
Have a circular (or nearly circular) orbit so constant conditions exist for its entire
year.
One more condition: “Large amounts of water must be available. Water is
2
essential for the chemical reactions leading to and sustaining life on Earth. Water
also appears to be important in controlling the amount of carbon dioxide, thus
avoiding run-away greenhouse effects that lead to run-away warming.” (op.cit.)
Our earth and the sun are suited to support life. What other good news can
we learn about our favorite planet?
The earth rotates like a top, but its axis of rotation is tilted 23.5 degrees. If
you take the tilt away, then we don’t have any seasons: no winter, no spring, no
summer and no fall. Some areas of the earth would always be too cold, and other
areas too hot.
The following figure is courtesy of “Windows to the Universe”,
www.windows.ucar.edu.
3
Notice that the tilt of the earth’s axis stays the same as the Earth rotates
around the Sun. But during the course of a year, there are times when the
Northern Hemisphere, where we live, is tilting away from the sun. We call that
4
winter. At other times the Northern Hemisphere is tilting toward the sun. We call
that summer.
The summer solstice occurs when the earth’s axis is most inclined toward
the sun. For us in the Northern Hemisphere it is the longest day of the year It
occurs on or about June 21.
The winter solstice occurs when the earth’s axis is most inclined away from
the sun. It is the shortest day of the year for us. It occurs on or about December
21.
Also notice from the figure there are times when the earth is tilting to the
“side.” In other words, the earth’s axis is not leaning toward the sun or away from
the sun. According to Google: “When the sun crosses the plane of the earth’s
equator, day and night is approximately the same length all over the world.” The
spring equinox just occurred on March 20. We call this date the beginning of
spring. Similarly, an autumnal equinox happens on or about September 22.
The figure below shows the path the sun takes across the sky on the
equinoxes and solstices.
5
Note that the path of the sun across the sky is longer on or about June 21
than it is at any other time. That’s why summers are warm (hopefully even here in
Rexburg ).
It is amazing when we consider the factors that make life possible here on
the earth. We’re a little like Goldilocks sampling the three bears’ porridge. One
bowl was too hot, another was too cold, but the third bowl was, according to her,
“just right.”
In terms of the earth we live on, we have a lot in common with Goldilocks.
6
If you would like to contact Weyland, his email address is
jack.weyland@gmail.com