قصة خرافية في الفضاء انجليزية

قصة خرافية في الفضاء انجليزية

Myth 1. The moon raises significant tides in people:

 There is no question that the moon, or rather its gravity, is the major cause of oceans tides on Earth. The sun’s gravity raises tides, too, by the way, but its effect is smaller. Some folks use the indisputable fact of the moon’s effect on the tides to argue that the moon raises tides in the human body. However, to believe that ocean tides and human tides both are caused by the moon betrays a major misunderstanding about how gravity works to produce ocean tides.

In short, gravity depends on two things: mass and distance. Tides are produced only when the two objects involved (say, the Earth and the moon) are both of astronomical size (far larger than a human!), and also close (astronomically) in distance. The moon is roughly 30 Earth diameters away from our planet, and roughly 1/80th of the Earth’s mass. Given that, the moon helps raise tides, which on average, are a couple of meters high in the fluid oceans.

If tidal effects were even measurable in the human body, which they aren’t, they would be on the order of a ten-millionth of a meter, or about one-thousandth the thickness of a piece of paper. Those are still tides, you say? Perhaps. But they are far, far smaller tides than are raised within your body when a truck passes you on the highway … or even when another person walks past you on the street.

So while the moon’s gravity can power the tides on Earth, its effect on a human body is utterly inconsequential.

Bottom line: Moon myths, take that! The moon doesn’t have a permanent dark side. The moon isn’t perfectly round. The moon is gray, like asphalt, not bright white. There is gravity on the moon. The moon may raise tides in people, but the tidal pull of the person sitting next to you is greater than that of the moon

Myth 2. There is no gravity on the moon :

 But of course the moon does have gravity. The idea that the moon has no gravity is frankly so ludicrous that I would not even mention it were it not so prevalent. Shown an image of one of the Apollo astronauts jumping high or seemingly floating across the lunar surface, some of my college students will reply that it is because there is no gravity on the moon. In reality, the force of gravity on the moon is only about one-sixth what it is on Earth, but it is still there.

I think that this moon myth, widespread though it may be, is simply a misunderstanding of what the word gravity means in physics. Every physical body, whether it be the sun, the Earth, the moon, a human body or a subatomic particle – everything that has substance – has a gravitational pull. While the practicality of measuring your weight (the pull of gravity) on tiny objects, such as a grain of sand, can be debated, the force exists and can be calculated. Even photons of light and other forms of energy exhibit gravity. Gravity holds galaxy clusters, galaxies, stars, planets and moons together and/or in orbit about each other. If every physical thing did not exhibit gravity, the universe as we know it could not exist.

   

Myth 3. The moon has a permanent dark side:

 Most grammar school students know that the moon presents only one face or side to the Earth. This is (roughly) true and gives rise to the idea that there is a permanently dark side of the moon, a thought immortalized in Pink Flyod’s music and elsewhere.

In fact, the side of the moon that is perpetually turned away from Earth is no more dark than the side we see. It is fully illuminated by the sun just as often (lunar daytime), and is in shade just as often (lunar night), as is the familiar Man in the Moon face we see.

The Earth-facing side of the moon gives rise to another misconception that many people share, namely that we see only 50% of the moon from Earth. In fact, only about 41 percent of the moon’s far side (a much more accurate and preferable term than dark side) is perpetually hidden from earthly observers. A diligent observer on Earth can, over time, observe about 59% of the moon’s surface. This is because a phenomenon called libration causes the moon’s viewing angle, relative to Earth, to change slightly over its orbit.

Lunar libration is due to the fact that the moon’s orbit around Earth isn’t a perfect circle. Instead, it’s a slightly elongated circle called an ellipse. Imagine a race car on an elliptical track. At each elliptical end of the racecourse, the car is flung out slightly due to the change in angle. It is a bit like rounding a corner. The result for the moon is that it occasionally exposes slightly more of its surface on the eastern or western extreme (depending on the location in the orbit). That’s why, as viewed from Earth, about 59% of the moon’s surface is exposed over the course of the moon’s (roughly) monthly orbit around the Earth.