- 3788 - FULL MOON - some things you should know? The moon’s orbit around the Earth is tilted 5 degrees compared to the plane of Earth’s travels around the Sun. The Earth itself is tilted 23.5 degrees causing our four seasons. All of these add up to make the Moon’s path through our sky higher or lower depending on the angles on any given night.
--------------------- 3788 - FULL MOON - some things you should know?
- The full Moon is very beautiful in the night sky. It looks like a perfectly round disk. However, you are probably more a romantic and less a nerd like most astronomers. The Moon is not perfectly round. It has a bulge around its waistline.
-
- The Moon’s girth is 2,159 miles but its height pole-to-pole is only 2,156.5 miles. It is two and one half miles shorter. The Moon is also elongated along the Earth-Moon axis. The cross-section is not a perfect circle. It is oblong shape with one of the ends pointing toward the Earth.
-
- Astronomers use these deformations from a perfect circle to explain the Moon’s history. Astronomers believe that a Mars-sized object hit the Earth 4,500,000,000 years ago. The oldest moon rock found is 4,300,000,000 years old. Debris from the collision splashed into orbit and the mass’ gravity pulled it together into a sphere.
-
- At that time the Moon was only 16,000 miles high in its orbit. Today it is 236,000 miles high in its orbit. The tidal forces of Earth-Moon gravity are slowly slowing it down and today the Moon is moving away from us at 3.8 centimeters per year (That is 1 and ½ inches for you Hoosiers).
-
- The Moon has a rotation. Its rotation on its axis is the same period as its rotation in orbit around the Earth. The current rotation period is 27 days, 7 hours, 43 minutes and 11.5 seconds. (That is 1 month for you Hoosiers).
-
- Astronomers call the Moon’s orbit to be in 1:1 resonance with Earth. But, it was not always like that. In its early history the Moon was in an elliptical orbit rather than a circular orbit and it was in 3:2 resonance with Earth. The Moon rotated 3 times for every 2 times it went around the Earth. The Moon’s spin was the outward centrifugal force that generated the bulge in the middle as the molten magma of a young Moon cooled to rock solid eons ago.
-
- Because both the Earth and the Moon are rotating in their individual orbit’s the time between two full Moons is different than the time of Moon’s rotation. The Moon’s phases repeat themselves every 29.53 days, called the “synodic month“.
-
- The Moon’s orbit is not a perfect circle either. Its distance from Earth varies from 221,460 miles to 252,700 miles. The Earth-Moon-Sun are in exactly the same positions every 6,585 days (18 years). If you observe a lunar eclipse, wait another 6,585 days and it will happen again.
-
- The sky on the Moon is always black because there is no atmosphere. On Earth the atmosphere scatters blue light to make the sky blue. It turns out that the molecules in the atmosphere are the same size as the wavelength of blue light. So, the blue light gets scattered the most making the sky blue.
-
- In addition to the black sky on the Moon, there is no sound. The Moon is a silent place. The Moon and the Earth got hit with about the same number of showers of asteroids. Some asteroids hit the surface of Earth but most burned up in Earth’s atmosphere. They all hit the surface of the Moon. Millions of asteroid craters on the Moon vary from 1,600 miles in diameter to the size of a toothpick’s diameter. With no atmosphere, no wind or rain, no erosion, these cosmic footprints are left intact.
-
- Most people are surprised with the fact that the Moon is ¼ the size of the Earth. Actually it is 27% the size, but only 1.2% the mass of the Earth (1/81st). The escape velocity to leave the Moon’s gravity is 5,200 miles/hour. The escape velocity for Earth is 25,000 miles/hour.
-
- The density of the Moon is 3,340 kg/m^3 which is 60% that of Earth. The force of gravity is 17% that of Earth. If you weigh 200 pounds on Earth, you would only weigh 34 pounds on the Moon. Yet, the gravitational tidal forces of the Moon are twice as strong as the gravitational forces of the Sun. The gravity of the Earth and the Moon exactly balance at 40,000 miles above the Moon.
-
- From the Moon the Earth always appears at the same place in the black sky. As you watch the continents spin around every 24 hours on Earth, the temperature on the Moon changes from 225 F on its day side to -243 F on its night side, a 468 degree F change in temperature. Makes for a cold night of sky watching.
-
- The full Moon is a beautiful sight. When astronauts visit again, the full Earth will be a beautiful sight as well.
-
- When the moon is low on the horizon it appears larger than when it is higher in the sky. It is an illusion. The idea that the curved atmosphere is magnifying the Moon is a myth. The illusion is really all in your head.
-
- To prove it to yourself make a tube from a rolled-up paper so the opening is just slightly larger than the moon when it rises. Tape the tube so the size stays fixed, then check later to see if the moon has changed sizes. The size is constant.
-
- Here is how the illusion works. The brain thinks things on the horizon are farther away that stuff overhead. Our brain interprets things as being bigger if it thinks they are farther away. Because we are used to seeing overhead clouds that are close compared to those on the horizon. Overhead they are 2 miles high, on the horizon they are 100 miles away. In the mind’s eye the sky is a flattened dome, or an inverted bowl. With this dome as our reference we expect something on the horizon to be father, and because it is actually no farther that when overhead our brains goof and imagine it to be larger.
-
- Better look tonight because the Moon is moving away from us by about 1.5 inches every year. You wait too long and you will loose your chance.
-
December 15, 2022 FULL MOON - things you know? 721 795 3787
----------------------------------------------------------------------------------------
----- Comments appreciated and Pass it on to whomever is interested. ---
--- Some reviews are at: -------------- http://jdetrick.blogspot.com -----
-- email feedback, corrections, request for copies or Index of all reviews
--- to: ------ jamesdetrick@comcast.net ------ “Jim Detrick” -----------
--------------------- --- Thursday, December 15, 2022 ---------------------------
No comments:
Post a Comment