Sky Watch: A backyard time machine
Nothing in the heavens appears as it is. It really is quite an illusion we experience nightly.
When people learn the immense distances of the stars and how long it takes their light to reach us on 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 summertime 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 summertime star groupings: the Summer Triangle.
The Summer Triangle is not a constellation; in fact, each of its three bright stars -- Vega, Deneb and Altair -- actually 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 remarkably far apart.
Altair lies about 100 trillion miles (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 1996.
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 trillions miles -- so far that we see it as it appeared in the sixth century. The light that leaves that star tonight won't arrive until the 35th century!
And 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 1988.
They might right now be watching as we celebrate the Winter and Summer Olympics and lament the rising cost of a first-class U.S. stamp from 22 cents to 25 cents. And they would undoubtedly be amused -- and befuddled -- by our fascination with such characters as Crocodile Dundee, Boy George and J.R. Ewing!
So 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.