|
Contrary to what some people might believe, the moon does not shine by its own light. |
AS THE CLOSEST
The moon is the Earth's only natural satellite and is about one-fourth the size of our planet. It is very close to the Earth by astronomical standards--an average distance of 238,855 miles. It would take about 5 months to get to the moon if you could drive a car there at a constant speed of 60 mph. If you flew an airplane to the moon, it would take about three weeks to get there. The Apollo astronauts got there in only a few days since they were traveling at much higher speeds than commercial aircraft. At the speed of light, a trip to the moon would take only 1.2 seconds.
Regardless of how long it takes to get there, you would weigh one-sixth of your earthly weight on the moon because of its weaker gravity.
The moon and Earth are bound by gravity, and the moon's gravitational attraction is what causes the tides on the Earth. The moon also helps maintain the Earth's 23.5 degree tilt, thus stabilizing our climate.
The same side of the moon always faces the Earth because the time it takes for the moon to orbit the Earth and make one complete rotation on its axis are the same duration--27.3 days. The Earth and moon are truly synchronized in more ways than we realize!
Contrary to what some people might believe, the moon does not shine by its own light. The moonlight we see actually comes from sunlight reflected off the moon's surface. If you could see the moon and Earth from high above their orbits, you would notice they were always half-lit.
However, viewing the moon from the Earth's surface makes things more interesting as the moon's orbit around the Earth and our consequent changing viewing angle causes the moon's different phases.
A new moon phase means the moon is between the Earth and sun and consequently invisible to our sight. From new moon, it begins to grow larger (also known as waxing) through crescent, quarter and gibbous phases on its way to becoming a full moon about two weeks later. After full moon phase, the moon begins to grow smaller (also known as waning) on its way to becoming a new moon about two weeks later.
One complete cycle of phases takes about 29.5 days, and the moon appears in different parts of the sky at different times of the day and night throughout this period.
Geologically, the moon is a dead place with no appreciable atmosphere. This lack of atmosphere contributes to huge temperature swings between day and night of approximately 250 degrees and minus 250 degrees respectively. Its surface consists of extinct lava plains, heavily cratered areas from meteor impacts, and mountain ranges.
The moon is subjected to a constant hail of impacts from micrometeorites, but there is no erosion or weathering on the moon from wind or water. As a result, many lunar features have remained relatively unchanged since they were created. In this sense, the moon is like a museum in space showing us its violent, distant past.
Twelve humans, all American, were fortunate enough to walk on the moon's ancient surface during the Apollo missions. Their foot prints will remain on the moon's surface for millions of years.
As an 8-year-old child in December 1972, I watched Apollo 17 on a black and white television from my elementary school's third-grade classroom. The ghostly images of the astronauts walking and driving across the lunar surface were awe-inspiring, mysterious and inspirational.
At that time, I imagined that we were on the brink of colonizing the moon for the advancement of the entire human race, but that was not to be. More than 35 years after the Apollo 17 astronauts left the moon, no other human has set foot on its surface. NASA is planning to return humans to the moon by the year 2020, but other countries like China, Japan, and India are now aiming for it as well.
As I gaze at the moon through my telescope with the same sense of amazement I had in 1972, I wonder when we will finally reach it again with the intent to stay.
January Skies
Mars dominates the long winter nights this month. Just a month past its closest approach to Earth, it is unmistakably bright. It can be seen well up in the east as the sky darkens after sunset. The moon will be very close to it during the evening of the 19th.
Saturn is next to rise in late evening. Although it's much dimmer than Mars in our sky, Saturn is truly the showpiece of the solar system. Next month's column will feature the ringed planet, but you can find it this month when it will be near the moon during the evening of the 24th.
Early morning risers can still catch brilliant Venus in the eastern sky. As the brightest object in the sky after the sun and moon, there is no mistaking Venus. On the morning of Jan. 4, it will be near the thin crescent moon.
Jupiter reappears in the morning sky later this month although it will be very low above the southeastern horizon. Look for it close to the brighter Venus during the last week of the month. On the mornings of Jan. 31 and Feb. 1, Jupiter and Venus will form a striking pair in the southeastern sky about an hour before sunrise.
David Abbou is a resident of Stafford County. He has been an amateur astronomer for more than 30 years and is a member of the Rappahannock Astronomy Club. Send questions or suggestions for future columns to david.