The Moon revolves around Earth in an elliptical orbit with a mean eccentricity of 0.0549. Thus, the Moon's center-to-center distance from Earth varies with mean values of 363,396 km at perigee to 405,504 km at apogee. The lunar orbital period with respect to the stars (sidereal month) is 27.32166 days (27d 07h 43m 12s). Moon Orbit Animation:The moon is tidally locked to the earth.One side of the moon always faces the earth.
Orbit andPhases of the Moon
Introduction
'Phase' refersto the fact that the moon shows differingamounts of lighted hemispheres as viewed from the earth during itsorbit around the earth.
'Cycle' refers to the repetition of these phases, as well as cyclesof eclipses. We will investigate these here.
Understanding the observed phases of the moon, requires understandinghow light and shadowing works in relation to the sun's light and theorbit of the moon and earth around the sun.
A superstition: It is sometimes believed that when the moon is bright and full, people act crazy. In fact, there is no statistical scientific evidence to support this. It is a myth.
Also: note that there are no monsters devouring the sun, as you mighthave been told if you were listening to a professor in 2000 BC.
One thing about studying moon phases: it begins to addressspecifically how what we see observe in astronomy has a very clear scientific explanation.
Motion of the Moon
First note that if you watch the moon night after night,you will see two key features which are fundamental cluesto understanding its motion:- It moves eastward against the background stars.
- It shows same face toward Earth in all phases.
Given these facts, can you infer if the moon rotates around its own axis?(figure 3-2)
Other Key Points:
Lunar Phases, Phase Cylce
Moon does not produce its own light, and so the light that we seefrom it is that which is merely reflected from the sun.
As the moon moves around the sky sun illuminates different amountsof its surface. The phase of the moon is thus entirely determined bylooking at the Earth's location relative to the sun. The best way to see the phases is to study figure (see also(figure 3-3) of text).
The Moon appears to go through a complete set of phases as viewed from theEarth because of its motion around the Earth, as illustrated below:
| Phases of the Moon |
In this figure, the various positions of the moon on its orbit are shown(the motion of the moon on its orbit is assumed to be counter-clockwise).The outer set of figures shows the corresponding phase as viewed fromEarth, and the common names for the phases.One can see the progression of phases:New, Waxing Crescent, First quarter, waxing gibbous, full,waning gibbous, 3rd quarter, waning crescent.
Note: the use of the word 'quarter' here does not refer to howmuch of the moon is visible, but the phase in the cycle.
Cycle of lunar phases takes 29.5 days this is the SYNODIC PERIOD.
Why is this longer than the SIDERIAL PERIOD which was 27.3 days?very simple: this is because the moon returns to the sameplace on the sky once every siderial period, but the sun isalso moving on the sky. When the moon returns to the samespot on the sky the sun has moved 27 degrees. Thus the moon now hasto take some extra time to catch up. (figure 3-4). The moon takes about 2 days to catch up.
(A good way to understand moonrise and moonset from thebook is to look at the picture on page 34 of the text)Imagine standing with the human figure on the globe Now the key point is that the horizon above which the moon isvisible, is the plane perpendicular to your body. The timeof the day is given by 'sunrise, sunset, noon, midnight.'Those times of day appear to us as the Earth rotates so that the USpasses through them. While the Earth rotates, the position of the moonin its orbit doesnt change much, so we can talk about moonrise and moonset.As you imagine the Earth turning and the various times of day passing you can see how the moonrise and moonset differs for different moon phases.)
Summary of Moon Motion and Phases
The moon appears to move completely around the celestial sphere once in about27.3 days as observed from the Earth (a siderealmonth) and reflects the corresponding orbital period of 27.3 daysThe moon takes 29.5 days to return to the same point on the celestial sphereas referenced to the Sun because of the motion of the Earth around the Sun (synodicmonth)
Lunar phases as observed from the Earth are correlated with thesynodic month.
Since the Moon must move Eastward among the constellations enough togo completely around the sky (360 degrees) in 27.3 days, it must move Eastwardby 13.2 degrees each day (in contrast, remember that the Sun only appears tomove Eastward by about 1 degree per day). Thus, with respect to the backgroundconstellations the Moon will be about 13.2 degrees further East each day.Since the celestial sphere appears to turn 1 degree about every 4 minutes, theMoon crosses our celestial meridian about 13.2 x 4 = 52.8 minutes later eachday.
Perigee and Apogee
The largest separation between the Earth and Moon on its orbit is calledMoon's Orbit Path
apogee and the smallest separation is called perigee.Rotational Period and Tidal Locking
The Moon has a spin period of 27.3 days that (except for smallfluctuations) exactly coincides with its (sidereal) period for revolution about the Earth.This is equivalent to saying that we see the same faceof the moon all the time, as was mentioned above.This is no coincidence; it is a consequence of tidal coupling between the Earth and Moon. This tidal locking of the periods for revolution and rotation, the Moon alwayskeeps the same face turned toward the Earth
| Bibliographic Entry | Result (w/surrounding text) | Standardized Result | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Faugh, Jerry S. & Serway Raymond A. College Physics. Pacific Grove: CA: Thomson Brooks/Cole, 2003. | Average Earth-Moon distance: 3.84 × 108 m | 768,000 km | ||||||||||||
| The World Book Encyclopedia. Chicago: World Book Inc., 2005: 783. |
| 768,934 km | ||||||||||||
| North, Gerald. Observing the Moon. United Kingdom: Cambridge University Press, 2005: 2. | 'It orbits the Earth at a mean distance of 384,000 km' | 768,000 km | ||||||||||||
| Sagan, Carl. Murmurs of Earth. New York: Random House, 1978: 226. |
| 768,800 km | ||||||||||||
| Jones, Brain. The Practical Astronomer. New York: Simon and Schuster Inc, 1990: 16. | 'However, the distance between the Earth and Moon varies from 356,410 km (222,756 miles) at perigee, or closest approach to 406,697 km (254,186 miles) at aposee, its farthest point'. | 712,820 km to 813,394 km | ||||||||||||
Download ringcentral meetings for mac. The moon is really just a large piece of rock, which was caught in the Earth's gravitational field. Because the moon has a smaller mass than the Earth, 7.35 × 1022 kg compared to 5.98 × 1024 kg, the moon orbits around the Earth, making the moon Earth's satellite. In fact, the moon is the Earth 's one and only natural satellite.
Orbit Of Moon Sun And Earth
So how was the diameter of the moon's orbit determined? One possible way would be finding the Earth-Moon distance. To find the Earth-Moon distance, scientists could use a RADAR laser, in which they can fire electromagnetic waves or em waves at the moon and time how long it takes for the em waves to travel to the moon and back. Since em waves always travel at the speed of light (3 × 108 m/s), and the time can be measured, one can use the equation v = s/t or s = vt, but don't forget to divide the measured time or the calculated distance by 2, as the em waves traveled twice the distance. The moon's distance from the Earth varies from 360,000 km to 406,000 km, making the mean distance from the Earth 384,000 km. Since its mean distance from the Earth is 384,000 km, the average length of the moon's orbit's diameter is 768,000 km.
Moons Orbit Tonight
Is the moon really moving farther away from the Earth? Yes, it is. The moon is moving about 3.8 cm farther away from the Earth every year. This occurs because of tidal interactions. The moon's gravitational force pulls on the Earth making it bulge ar the face of the Earth the moon is facing. These are called 'tidal bulges'. The tidal bulges would affect the force of gravity on the moon, as the bulge would have a greater gravitational pull on the moon than the center of the Earth. And since the Earth rotates faster than the moon orbits, the tidal bulges would move ahead of the moon and pull the moon towards the tidal bulge causing the moon to speed up and move ahead in its orbit. Note: The moon is only moved very little by this in a day, so don't get crazy.
Moon's Orbital Period
Collin Tam -- 2005