Astronomy pictures
To go to the University of Nebraska-Lincoln Astronomy animations page click here.
Stars give off electro-magnetic (EM) energy in the form of waves. These waves can be so small that they are often measured in nano-meters. A human hair is about 60,000 nanometers thick. Electro-magnetic energy waves that are about 500 nanometers long are perceived as visible light. Red light has slightly longer waves than violet waves. Any waves much bigger or smaller than 500 nanometers are invisible. They can still effect us, though. Ultra-violet light has a wavelength of about 250 nanometers and is what gives you a sunburn. X-rays have a wavelength of only .5 nanometers and can go right through the soft human tissue, but not bone. This is why x-rays are great for taking pictures of inside your body. For a great short video and interactive quiz on the electro-magnetic spectrum click here.
Seasons
The Earth rotates around an axis. The Earth's axis does not stand straight up and down, but is tilted by 23.5 degrees. In the Northern Hemisphere, the Earth's axis always points towards the North Star (Polaris). Because the Earth is revolving around the Sun, sometimes the Northern Hemisphere will be tilted towards the Sun and sometimes it will be tilted away. To be clear, the tilt doesn't change; Earth's location in its orbit is what's changing.
When the Northern Hemisphere is tilted towards the Sun it is Summer. When the Northern Hemisphere is tilted away from the Sun it is Winter. Notice the person standing on the Earth. His location on Earth is the same for both Winter and Summer. However, In Summer the Sun is almost directly over his head. In Winter, the Earth would be lower in his sky. When the sun is high in the sky, the solar energy coming to Earth is more direct. When the Sun is low in the sky, the solar energy coming to Earth gets more spread out.
The Earth rotates around an axis. The Earth's axis does not stand straight up and down, but is tilted by 23.5 degrees. In the Northern Hemisphere, the Earth's axis always points towards the North Star (Polaris). Because the Earth is revolving around the Sun, sometimes the Northern Hemisphere will be tilted towards the Sun and sometimes it will be tilted away. To be clear, the tilt doesn't change; Earth's location in its orbit is what's changing.
When the Northern Hemisphere is tilted towards the Sun it is Summer. When the Northern Hemisphere is tilted away from the Sun it is Winter. Notice the person standing on the Earth. His location on Earth is the same for both Winter and Summer. However, In Summer the Sun is almost directly over his head. In Winter, the Earth would be lower in his sky. When the sun is high in the sky, the solar energy coming to Earth is more direct. When the Sun is low in the sky, the solar energy coming to Earth gets more spread out.
The Moon
Can you find Rona, her hair, and her basket?