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A Celestial Time Machine


Last updated 9/14/2023 at 11:23am

The Summer Triangle is not a constellation; in fact, each of its three bright stars – Vega, Deneb and Altair – lies in a separate constellation from the others.

If you've ever wished you could travel back in time like Marty McFly in "Back to the Future," you may be out of luck. But if you'd like to stay right where you are and see into the past, well, that's something you can do quite easily. All you've got to do is step outside on a clear night and gaze skyward!

The fact is that everything in the heavens appears not as it is now, but only as it was long ago. That's because the light that strikes our eyes must travel across space, and the longer its journey, the farther into the past we can peer.

Seeing back into time like this helps astronomers learn how the stars and galaxies appeared in the distant past and, therefore, how the universe has evolved over time.

Geologists and paleontologists use this technique frequently. The deeper into a canyon they explore, for example, the older the sediment layers they find, and, from these, they can learn the history of our planet and its diverse and ever-changing life forms.

Right now, as summertime settles upon us once again on our part of planet Earth, we have a great opportunity to begin our journey through time and space with one of the most famous of all star groupings: the Summer Triangle.

The Summer Triangle is not a constellation; in fact, each of its three bright stars – Vega, Deneb and Altair – lies in a separate constellation from the others. And, though these three stars appear roughly the same brightness, they are not even close to the same distance from us. In fact, they're quite distant from one another.

Altair lies about 98 trillion miles (17 light years) from us. In other words, its light has been traveling through space for nearly 17 years. This means that the photons of light from Altair that strike our eyes tonight have been journeying since 2006.

Vega, on the other hand, lies about 50% farther away than Altair – at a distance of about 147 trillion miles (25 light years). And Deneb lies some 15,000 trillion miles, or about 2,600 light years, from us – so distant that we see the light it emitted in the sixth century BC. The light it emits tonight won't arrive here for another two and a half millennia! And these are some of the nearest stars!

It all becomes even more mind-boggling when we consider how fast light travels. The speed of light is nearly 671 million miles per hour; this means that, in just one second, a beam of light can cross 186,282 miles of space!

Let's put that number into perspective. Stand outdoors some night and watch an Earth-orbiting satellite cross the sky. That satellite is moving at about 17,000 miles per hour and can complete one orbit of the Earth in just 90 minutes. That's fast by human standards, but during that same time, a beam of light could orbit the Earth more than a million times!

The next time you gaze skyward on a clear night, ponder all the amazing events that have occurred here on our planet during these long journeys of starlight.

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