Ask Me Help Desk - Flight to the moon versus Orbits & the revolving of earth and the theory of relativit

Hi there,
I am not a scientist at all but I have many questions... I wonder how does an Astronaut orbit the earth in the way to the moon? Does the aircraft simply "escape any orbit as it reaches the moon? Is it possible?Does he fly at 23000 KM/h when at a LEO orbit? Isn't it harmful to him and why?
I heard it is possible to say according to the theory of relativity that the sun revolves around the earth.Wikipedia says that: Albert Einstein was able to show that gravity is due to curvature of space-time, and that orbits lie upon geodesics and this is the current understanding. I don't know 100 % what it means but can anyone help me understanding this questions? If this is true what happens with the Astronaut at space in the way to the moon? Does he enter some sort of orbit around the earth together with the stars?
Thanks for any answer.

Hello betzaleldaniel. Wow - a lot of questions! Let me try to help with a few.

Quote:

Originally Posted by betzaleldaniel

I wonder how does an Astronaut orbit the earth in the way to the moon? Does the aircraft simply "escape any orbit as it reaches the moon? is it possible?Does he fly at 23000 KM/h when at a LEO orbit? Isnt it harmful to him and why?

When the Apollo missions went to the moon their procedure was to first enter earth orbit, and after a few revolutions they would fire the engines on the 3rd stage of the Saturn V rocket to get enough added velocity to coast up to the moon. In low earth orbit their velocity was about 17KMPH. They then fired their rockets to provide enough velocity to escape earth orbit and travel out to the moon, in a move called "translunar injection" which gave them about another 6 KMPH. That's what it takes to be able to "coast" away from earth all to a point close enough to the moon for the moon's gravity to become strong enough to outpull the earth's gravity, at which point they would start falling toward the moon. Here's some info on trans-lunar injection:

Trans Lunar Injection - Wikipedia, the free encyclopedia

Quote:

Originally Posted by betzaleldaniel

I heard it is possible to say according to the theory of relativity that the sun revolves around the earth. ....If this is true what happens with the Astronaut at space in the way to the moon? does he enter some sort of orbit around the earth together with the stars?

Not sure what "theory of relativity" you mean here. Under two-body orbital mechanics (such as the earth-sun system) both bodies orbit about a common point, which is the center of mass of the two bodies. Since the sun is so much more massive than the earth, the center of mass in the sun-earth system is close to the center of the sun itself, so for all practical purposes one can think of the sun as essentially stationary and the earth revolves around it. Also, keep in mind that the solar system is a complicated place with planets much more massive than the earth, so in fact the sun is affected much more by the gravitational effect of Jupiter than it is by earth. As for the astronaut on his way to the moon - because he his velocity is less than the escape velocity from earth, if he didn't encounter the moon on his way "up" he would eventually slow down and ultimately start falling back to earth, so in a sense yes, he is still in some sort of orbit of earth.

Quote:

Originally Posted by betzaleldaniel

Wikipedia says that: Albert Einstein was able to show that gravity is due to curvature of space-time, and that orbits lie upon geodesics and this is the current understanding. I dont know 100 % what it means but can anyone help me understanding this questions?

Einstein's model of space-time and gravity is difficult to grasp - I am not an expert on this, so I'll leave it to others to clarify - if you've read the various articles in Wikipedia already you may want to consider reading a book or two on the subject. Unfortunately most fall into two categories - either very technical and difficult to follow (like college texts) or non-technical and full of "gee whiz" facts that really can't give a full understanding.

You also have to remember that the solar system is orbiting the center of our galaxy and it's all moving through space.

Quote:

betzaleldaniel> Wikipedia says that: Albert Einstein was able to show that gravity is due to curvature of space-time, and that orbits lie upon geodesics and this is the current understanding. I don't know 100 % what it means but can anyone help me understanding this questions?

I think what you're talking about is the idea of warped space. Think of space as a rubbery plane. Mass would cause a 'dimple' in the plane and other bodies would circle the dimple like water circling a drain (tho I think it's speed that keeps them from 'falling in' - but it wouldn't be enough for a black hole which would eventually draw them in despite speed of circle. The pull of the enormous gravity would overcome it.)

Maybe instead of a book, try popular science magazines. Maybe Discover or Scientific American or New Scientist would allow you to search their online archives for related stories. They should be tech enough to clear up a few things but easy enough for a non-physicist to understand.

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Answer with the Compliments of World Book:-

MOON/How the moon moves

The orbit of the moon. The moon travels around the earth in an elliptical (oval shaped) path called an orbit. One such trip around the earth is called a revolution. The moon moves at an average speed of about 2,300 miles (3,700 kilometers) per hour along its 1.4-million-mile (2.3-million-kilometer) orbit.

The moon also travels with the earth as the earth circles the sun every 3651/4 days, an earth year. The moon actually moves from west to east in the sky. But it seems to move from east to west as it rises and sets because the earth spins much faster than the moon revolves around the earth.

Because the moon's orbit is oval, the moon is not always the same distance from the earth. The point where the moon comes closest to the earth is 221,456 miles (356,399 kilometers) away. This point is called the moon's perigee. The moon's farthest point from the earth is 252,711 miles (406,699 kilometers) away. This point is the moon's apogee.

The gravitational pull of the earth keeps the moon in its orbit. If the earth or its gravitational force were to suddenly disappear, the moon would no longer orbit the earth. But the moon would still move in orbit around the sun.

Scientists measure the moon's revolution around the earth in synodic months and sidereal months. A synodic month--which equals about 291/2 days--is the period from one new moon to the next new moon. It is the time that the moon takes to revolve around the earth in relation to the sun. If the moon started on its orbit from a spot exactly between the earth and the sun, it would return to almost the same place in about 291/2 days. A synodic month equals a full day on the moon. This lunar day is divided into about two weeks of light and about two weeks of darkness.

A sidereal month--about 271/3 days--is the time the moon takes to make one trip around the earth in relation to the stars. If the moon's revolution were to begin on a line with a certain star, it would return to the same position about 271/3 days later.

A synodic month is longer than a sidereal month because the earth travels around the sun while the moon travels around the earth. By the time the moon has made one revolution around the earth, the earth has revolved 1/13 of the way around the sun. Therefore, the moon has to travel slightly farther to be in the same position in relation to the sun.