Seeing into the Distant Past with Mobile Astronomy Apps

Did you know that if you gaze up at a clear evening sky, you’re actually looking into the past? Even with the naked eye, you can see starlight that was emitted years — or even centuries — ago. And if you know where to look, you can see galaxies so far away that their light has been traveling since before humans walked the Earth. Add the magnifying power of a telescope, and you’ll journey to the time when dinosaurs lived. In this edition of Mobile Astronomy, we’ll travel the celestial and see ancient starlight with our own two eyes.

Starlight is the visible part of an electromagnetic spectrum of radiation that our eyes have evolved to detect. Beyond the visible range are radio waves, X-rays and infrared. In the vacuum of space, electromagnetic radiation travels at a speed of 186,282 miles per second (or 299,792 km/s), usually denoted with a “c.” Albert Einstein showed that the speed of light is the top speed possible in the universe. Because of this, light from distant objects takes a long time to reach our eyes.

Space is so vast that distances soon become cumbersome to convey using everyday units. To write out the distance in miles to a nearby galaxy, you would need 19 zeros! As such, astronomers have adopted the term “light-year” — the distance light travels in a vacuum in one year. It’s 5,878,625,541,248 miles (9,460,730,743,054 km), or almost 6 trillion miles (more than 9 trillion km)! See what I mean? [Einstein’s Theory of General Relativity Explained (Infographic)]