Popular Astronomy

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Earth

Image: NASA

 

 

 

Amazing fact!

An astounding 40,000 tons of dust from disintegrated comets and asteroids falls to the Earth's surface every year! It may sound a lot, but it would take 10 billion grains of dust to fill a square on the Earth measuring one metre by one metre.

 

 

 

 

     Our home, the third ‘rock’ from the Sun. Yes, we live on a planet just like those we see in the sky such as Venus, Mars and Jupiter. Well, not exactly like them. You see, Earth is the only planet (that we know of) that has life. Why is this, you ask? Well, if you remember the story of Goldilocks, she kept trying the porridge until she found a bowl that was neither too hot nor too cold – it was just right for her. Well, in the same way, Earth is just right for us. It is at a distance from the Sun (149.6 million kilometres) that the temperature never gets too hot, or really too cold (well maybe at the poles, or those horrible winter mornings when you have to go to school in

Earth and Moon

The Earth and Moon, as seen from a spacecraft on its way to an asteroid. Image: NASA/JHUAPL

the dark). It is just the right temperature for liquid water, and that is important because life as we know it needs water to survive. In fact, astronomers call the region around a star where the temperature is just right for liquid water the ‘Goldilocks zone’. Earth is slap bang in the middle of the Sun’s Goldilocks zone, and is the only planet with oceans of water, although as we shall see there is lots of frozen water on Mars, which is just outside the Goldilocks zone.

      Another important feature of planet Earth is its atmosphere. Of course, this contains the oxygen that we breathe. Now, let’s just clear one thing up – the atmosphere is not blue! Although it may look that colour when you look up at a clear blue sky (although with all the cloud we get you would be forgiven for thinking the atmosphere was actually grey!). The blue that you see is because the atmosphere scatters light from the Sun, and it scatters blue light more than the other colours. So the blue light is bouncing around all over the place off tiny particles in the atmosphere before entering your eye, so it seems to come from all over the sky. That is why a clear sky looks blue.
      The Earth has seasons because it is tilted a little bit. If you could measure the Earth with your protractor you would find that it is slanted at an angle of 23 degrees as it spins around. So as it orbits the Sun, for half the year the Northern Hemisphere (i.e. Europe, USA, Russia) is closer to the Sun (and hence we get our summer) and for the other half of the year the Southern Hemisphere (i.e. Australia, Africa and South America) is closer (and we get our winter).

Moon

The Earth's trusty neighbour, the Moon.

Image: Robin Scagell

    

     Earth has one Moon, which of course we often see in the sky. Throughout a month it will change shape, or what astronomers call ‘phase’. This is because the Moon is orbiting around the Earth, and the amount of sunlight that falls on the face of the Moon that we can see is constantly changing. The Moon always shows the same face to the Earth. To see around the back we have to send spaceships. It is covered in ancient plains of dried up lava and pitted with craters. The Moon doesn’t have an atmosphere or weather to erode the craters. That means the craters will stay there practically forever, as will the boot prints of the 12 astronauts who walked around on the Moon.

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