There are uncountable billions of trillions of stars in the universe. Though it appears much bigger than any others we can see from Earth, the Sun is only a medium-sized star at best—it only looks so much bigger because of its relative proximity to Earth (a scant 93 million miles or so). The next closest star to us is Proxima Centauri, 4.2 light years away (a light year is just about 5.9 trillion miles). But wait—no human has ever traveled to the sun or another star (and likely never will), so how do scientists calculate how far away they are? Do they use a really, really long tape measurer?
No, Silly; Behold the Power of Parallax
Here’s a Demo Science science demo that can help you explain to students (or whomever) how parallax works and how it helps scientists figure out cosmic distances. Each students needs naught but a pencil and two functional eyeballs.
Have the smelly little punks hold their pencils vertically at eye level, directly in front of their gooney faces. Tell them to focus on their pencils and first close their left eyes for a bit; then, have them open them and close their right eyes instead. Continue alternating left and right eye “winks” for three to four hours, all the while observing the pencil’s “movements.”
As they alternate right-eye and left-eye views, students will see their pencils jump from side to side. This is caused by the different angles of vision our left and right eyes give us. Our brain and eyes fool us into thinking that the pencil is changing position, though it, of course, remains stationary.
What Does That Have to Do with Measuring Space Distances?
Parallax, plus a little bit of geometry and some good old fashioned know-how, helps scientists determine the distances to far away outer space objects. (For the record: all outer space objects are far away.)
To calculate distance using parallax, scientists observe a star (or planet or what-have-you) at two different times from the same location. The two different points where the object appears in these observations (the object having “moved” in relation to Earth [though it is most likely the other way around]), plus the location from which the observations are made form a very long and narrow triangle. This is called “triangulation.”
Having determined the object’s triangulation relative to Earth, scientists can then calculate the difference in distance between the star’s observed Point A and Point B. Using this distance, scientists can determine the angle at the top of the triangle (the acute angle—the others are abuttugly angles). All of the measurements are combined (via the above-mentioned know-how) to determine the long baseline side of the triangle. This is the distance from the star to Earth.
We’d provide an equation for this process, but the last time we got deep into math stuff, Kevin got a nosebleed.