Wednesday, June 20 , 2018, 8:49 am | Overcast 60º


Dennis Mammana: A Backyard Time Machine Is Right Before Our Eyes

When you look up into the night sky, you’re looking into the past. Click to view larger
When you look up into the night sky, you’re looking into the past. ( illustration)

Nothing in the heavens appears as it is. It really is quite an illusion we experience nightly.

When folks learn the immense distances of the stars and how long their light requires to reach Earth, they wonder if astronomers are bothered that stars and galaxies do not appear as they are now but only as they were long ago.

The answer is a simple “No, we’re not.” In fact, the greater the distances — and, therefore, the further back into time — that we can peer, the happier we are, because this enables us to see how the stars, galaxy and universe appeared in the distant past. If all we could see were light from today, we’d never learn how things have evolved over time.

Geologists and paleontologists use this technique frequently. The deeper into a canyon they go, 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.

So in a sense, the heavens are a great backyard time machine, and traveling to distant eras is as easy as stepping outdoors and looking up. And right now, as autumn descends upon us once again here 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 nighttime 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 at all the same distance from us. In fact, they’re separated by tremendous distances.

Altair lies about 100 trillion miles (nearly 17 light-years) from us. In other words, its light has been traveling through space for 17 years. This means that its photons of light that strike our eyes tonight have been traveling through space since the year 2000.

Vega, on the other hand, lies 50 percent farther away than Altair, at a distance of about 147 trillion miles (25 light-years). And Deneb lies some 8,200 trillion miles (around 1,400 light years) —so far that we see it as it appeared in the seventh century. The light that leaves that star tonight won’t arrive until the 35th century!

Just as the light of these stars takes time to reach Earth, light from our world takes time to reach them. Imagine, for example, if astronomers living on a world orbiting Vega had telescopes powerful enough to see activity on our planet. They could see us as we were in 1992.

They might now be watching in real time as the Summer Olympics begin in Barcelona, Spain, or as space shuttle Endeavour makes its maiden voyage. And they would surely be scratching their little green heads over such television characters as Jerry Springer, Al Bundy and Ren & Stimpy.

The next time you gaze skyward on a clear dark night, think about all the amazing events that have taken place on our planet during these long journeys of starlight.

Dennis Mammana is an astronomy writer, author, lecturer and photographer working from under the clear dark skies of the Anza-Borrego Desert in the San Diego County backcountry. Contact him at [email protected] and follow him on Twitter: @dennismammana. Click here to read previous columns. The opinions expressed are his own.

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