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Light-Year
Light-Year
Space is so huge, that miles are not a big enough unit to measure distances in space. Astronomers measure objects in the Universe using light-years. A light-year is the distrance light travels in one year. The Andromeda Galaxy is the closest galaxy to the Milky Way. It is a spiral galaxy approximately 2,500,000 light years away. This means in takes a light wave 2,500,000 years to travel from the Andromeda Galaxy to us in the Milky Way Galaxy. By the way, our Milky Way Galaxy is about 100,000 light-years across!
To help you understand a light-year, check out the link to a light-year animation.
Stars
Stars
Not all stars look the same. Each has it's own characteristics, including our own star, the Sun. Learning about other stars helps us to learn more about our Sun. One way to organize the characteristics of stars with with a Hertzsprung-Russell diagram (H-R diagram).
Gif-tionary explaing the lift cycle of a star
Click on Stella Evoluation on the left side of the screen. Then select "Low Mass Star Evolves - See from Outside"
http://www.valdosta.edu/~cbarnbau/astro_demos/frameset_distance.html
Click on "Distances from the Sun - The general idea"
http://www.valdosta.edu/~cbarnbau/astro_demos/frameset_distance.html
Doppler Effect
Doppler Effect
So, how do scientist know if the Universe is expanding? The answer is: by studying light waves using the Doppler effect. Imagine that the image below is of a parked car with someone holding down on the horn.
Really annoying, right? The sound would stay at a constant pitch. Now lets imagine the car horn got stuck, the owner of the car is so embarrassed that they decide to drive off. As the car moves the sound wavelengths start to change. Look at the image below. You can tell that the car is moving to the right because the sound waves are bunched up, or have a short wavelength, in the direction the car is moving. As the car is leaving there is a long wavelength.
The wavelengths are shorter in the direction the car is moving. If the car was moving closer to you, you would here a higher pitch. The wavelengths are longer behind the noisy car. Once the loud car passes you, you would hear a lower pitch.
Super awesome interactive explaining the Doppler Effect
http://www-tc.pbs.org/wgbh/nova/assets/swf/1/doppler-effect/doppler-effect.swf
Doppler Effect animation
http://www.pbs.org/wgbh/nova/universe/movi_flash.html
http://www.valdosta.edu/~cbarnbau/astro_demos/frameset_distance.html
Light Waves
Light Waves
Light waves behave in the same fashion. As an object that gives off light waves moves closer to us, the wavelengths are shorter. If the object is moving away from us, the wavelengths are longer.
We still haven't answered the question yet! How do scientist know that the Universe is expanding? Let's pause for a moment and talk about color. Yep, that's right. Color. Why do we see color? Using a prism, white light can be broken up into each individual color wavelength (it's also how a rainbow is created).
Each color is a different wavelength.
The color of an object is the wavelength of light reflected, all other colors are absorbed by the object. For example, a banana reflects the yellow wavelength. Red, orange, green, blue, indigo, and violet are absorbed by the banana.
Which color has the longest wavelength? Red
Which color has the shortest wavelength? Violet
Let's get back to the main question: How do scientist know that the Universe is expanding? Scientist study the light from objects far in space. They gather the light and break it up into each wavelength of color. Some parts of the light are absorbed creating absorption lines. If the absorption lines are shifted to the blue, then the object is moving toward us (short wavelengths). If it is shifted toward the red, then the objects is moving away from us (long wavelengths).
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