Did you ever notice that the Moon always looks the same? Sure, it waxes and wanes from a new moon to a full moon, but the bright and dark patches on the Moon always look the same. In fact, these features are so familiar that people call it the Man in the Moon.
This is because the Moon always points the same face towards the Earth. The Moon does actually rotate on its axis, it's just that the amount of time it takes to make a complete orbit around the Earth matches the amount of time it takes to complete one rotation. In both cases, this is 27.3 days.
So, when you hear people refer to the far side of the Moon, they're talking about the part of the Moon that always faces away from the Earth. Until we sent spacecraft into orbit around the Moon to take pictures, nobody on Earth had ever seen what the far side of the Moon looks like.
But why does this happen? Over the few billions years since its formation, the Moon has become tidally locked with the Earth. In the distant past, the Moon had different rotation and orbital speeds, and it showed all of its sides to our planet. But the gravity of the Earth tugged at the irregular shapes on the Moon, causing it to slow its rotation down until it was exactly the same length as its orbit.
The Earth, on the other hand, has so much mass that the force of gravity from the Moon pulling on Earth can't overcome its rotational speed. The Moon does create the tides, though, and causes the ground to rise and fall - it's just such a small amount that you can't feel it.
Sometimes people mistakenly call this the dark side of the Moon. But there is no dark side of the Moon. Think about it, when we're seeing a new moon, that's because the familiar part that we can always see is in shadow. But at that point, the far side will be bathed in sunlight.
Tuesday, July 8, 2008
The Moon
How Does the Earth Protect Us From Space?
Answer: Our Earth keeps us very safe from a dangerous Universe that's always trying to kill us in new and interesting ways.
Risk: Cosmic rays are high energy particles fired at nearly the speed of light by the Sun, supermassive black holes and supernovae. They have the ability to blast right through your body, damaging DNA as they go. Long term exposure to cosmic rays increases your chances of getting cancer. Fortunately, we have our atmosphere to protect us. As cosmic rays crash into the atmosphere, they collide with the oxygen and nitrogen molecules in the air.
Risk: Gamma rays and X-rays. As you know, radiation can damage the body. Just a single high-energy photon of gamma rays can cause significant damage to a living cell. Once again, though, the Earth's atmosphere is there to protect us. The molecules in the atmosphere absorb the high-energy photons preventing any from reaching us on the ground. In fact, X-ray and gamma ray observatories need to be built in space because there's no way we can see them from the ground.
Risk: Ultraviolet radiation. The Sun is bathing the Earth in ultraviolet radiation; that's why you get a sunburn. But the ozone layer is a special region of the atmosphere that absorbs much of this radiation. Without the ozone layer we would be much more exposed here on the surface of the Earth to UV rays, leading to eye damage and greater incidence of skin cancer.
Risk: Solar flares. Violent explosions on the surface of the Sun release a huge amount of energy as flares. In addition to a blast of radiation, it often sends out a burst of plasma traveling at nearly the speed of light. The Earth's magnetosphere protects us here on Earth from the effects of the plasma, keeping it safely way from the surface of the planet. And our atmosphere keeps the X-ray/gamma ray radiation out.
Risk: Cold temperatures. Space itself is just a few degrees above absolute zero, but our atmosphere acts like a blanket, keeping warm temperatures in. Without the atmosphere, we'd freeze almost instantly.
Risk: Vacuum. Space is airless. Without the Earth, there'd be no air to breath, and the lack of pressure damages cells and lets water evaporate out into space. Vacuum would be very, very bad.
Friday, July 4, 2008
Q & A
Q: What element is most plentiful on the Sun?
A: Hydrogen. The Sun is made up of about 75% hydrogen and 25% helium. About 0.1% is metals (made from hydrogen via nuclear fusion). This ratio is changing over time (very slowly), as the nuclear reactions continue, converting smaller atoms into more massive ones.
Q & A
Q: Why can't we see gravity?
A: First of all, we can only see the light that is reflected from things (we don't see the thing itself), and gravity doesn't reflect light. Gravitational lensing, however, is the displacement of light due to the warping of space by a gravitational lens (a massive object in space that bends light that passes by it, due to the gravitational forces). This is a way that gravity can be "seen."
Friday, May 30, 2008
Amazing Stonehenge Mistery Solved
This video is amazing, this guy shows the whole world how the Stonehenge was build. It’s just a matter of ingenuity. Just move the bigger rock with the help of smaller ones, and gravity. It’s amazing, just watch it.
Connie Talbot
Her's first song in Britain's Got Talent
In the FINAL
and Over The Rainbow ALBUM
Monday, May 12, 2008
Why do stars twinkle?
The scientific name for the twinkling of stars is stellar scintillation (or astronomical scintillation). Stars twinkle when we see them from the Earth's surface because we are viewing them through thick layers of turbulent (moving) air in the Earth's atmosphere.
Stars (except for the Sun) appear as tiny dots in the sky; as their light travels through the many layers of the Earth's atmosphere, the light of the star is bent (refracted) many times and in random directions (light is bent when it hits a change in density - like a pocket of cold air or hot air). This random refraction results in the star winking out (it looks as though the star moves a bit, and our eye interprets this as twinkling).
Stars closer to the horizon appear to twinkle more than stars that are overhead - this is because the light of stars near the horizon has to travel through more air than the light of stars overhead and so is subject to more refraction. Also, planets do not usually twinkle, because they are so close to us; they appear big enough that the twinkling is not noticeable (except when the air is extremely turbulent).
Stars would not appear to twinkle if we viewed them from outer space (or from a planet/moon that didn't have an atmosphere).
Sunday, May 11, 2008
What do you weigh on other planets?
http://www.enchantedlearning.com/subjects/astronomy/
Why is the sky blue?
Sunlight is made up of all the colors of the rainbow: red, orange, yellow, green, blue, and violet. The gas molecules in the atmosphere interact with the sunlight before the light reaches our eyes.
The gas molecules in the atmosphere scatter the higher-energy (high frequency) blue portion of the sunlight more than they scatter the lower-energy red portion of the sunlight (this is called Rayleigh scattering, named for the physicist Lord John Rayleigh). The Sun appears reddish-yellow and the sky surrounding the Sun is colored by the scattered blue waves.
When the Sun is lower in the horizon (near sunrise or sunset), the sunlight must travel through a greater thickness of atmosphere than it does when it is overhead, and even more light is scattered (not just blue, but also green, yellow, and orange) before the light reaches your eyes. This makes the sun look much redder.
Caution: Never stare directly at the Sun.
How Big Do Numbers Get?
American
million 6(zeroes) 10^6 1,000,000
billion 9 (10^9) 1,000,000,000
