Have you ever wanted to see for yourself what the universe was like 1,000 years ago, 1,000,000 years ago, or even more than 1,000,000,000 years ago? Well, that is what astronomers do every day.
Remember that what we see with our eyes are images formed with light reflecting off the objects around us and into our eyes. But even light needs time to travel across space!
A quick google search of the phrase “speed of light” gives me c = 299 792 458 m / s. This value is the speed of light in vacuum.
Just in case you’re wondering, yes, the speed of light varies in other mediums, like air, water, glass, and so on. However, the speed of light in air is sufficiently close to that in vacuum (Index of Refraction of air = 1.0003 , that is the difference between the speed of light in vacuum and that in air is 0.03%), so in most cases we can considered it to be the same.
Back to the topic at hand…
If you see your friend approaching from 100 m away, you’re actually seeing an image of your friend from 0.000000334 seconds ago. Why? Because it took that amount of time for the light bouncing off your friend to reach your eyes. Of course, 0.000000334 seconds is very quick, much quicker than a blink of the eye. At the same time, that’s because your friend is only 100 m away. What about objects further than that?
The distance from the moon to the earth (equator to equator) according to NASA is 378,000 km . So when you’re looking at the full moon at night, you’re actually looking at the moon as it was 1.26 seconds ago.
1 lightyear = 94,605,284,000,000 km, that is the distance that light travels in a year.
Let’s look at something even further. The nearest known galaxy to Milky Way is Andromeda, shown above, and it is located 2,500,000 light years away. That means when astronomers use their powerful telescope to take a peek at Andromeda, they’re looking at an image of Andromeda 2.5 million years ago .
The furthest galaxy ever captured to date with the Hubble Space Telescope (shown below) is located 13.2 billion lightyears away, and NASA estimate the age of the universe is approximately 13.7 billion years old . So the image NASA captured is of that galaxy 13.2 billion years ago, i.e. near the beginning of the universe (relatively speaking of course).
So if you want to look at history, simply look toward the stars…
P.S. There is more to to come on this topic, come back and check in a week or two….
 Kaku, M. Physics of the Impossible: A Scientific Exploration Into the World of Phasers, Force Fields, Teleportation, and Time Travel. Canada: Random House of Canada, 2009.
 NASA, “Solar System Exploration, Earth’s Moon: Facts and Figures” [online], Available: http://solarsystem.nasa.gov/planets/profile.cfm?Display=Facts&Object=Moon
 NASA, “Amazing Andromeda Galaxy” [online], Available: http://www.nasa.gov/vision/universe/starsgalaxies/spitzerf-20061003.html
 NASA, “NASA’s Hubble Finds Most Distant Galaxy Candidate Ever Seen in Universe” [online], Available: http://www.nasa.gov/mission_pages/hubble/science/farthest-galaxy.html