Distance

Late on Sept. 6, a cold, clear night at Lakeside, Tooele County, I aimed my telescope at a galaxy called NGC7479 in the constellation Pegasus, and started making images. It’s a classic barred spiral, shaped like a backwards S, with a pair of long arms wrapped around the center.
The night was so cold that I spent hours in our Jeep, occasionally idling the motor with the heater on, listening to satellite radio and letting astronomy software take the photos. I would pop out to check on progress as pictures showed on the laptop screen, take a short walk in the starlight, then jump back inside and try to warm up. The Jeep’s thermometer read 40 degrees, then 39, but it felt much colder.
From 11:42 p.m. on Sept. 6 until 5:03 a.m. on Sept. 7, I shot hundreds of astrophotos of the galaxy, mostly at 30 seconds exposure. For half an hour starting at 5:19 a.m. I took “flats,” pictures of nothing except dust doughnuts and other flaws in the camera and telescope optics. Flats are used to correct these problems during processing.
The color images were not good, but the luminosity, or black-and-white views, were all right. I cleaned up 76 of them using flats and a later image called a “bias” view (made to cut out artifacts created by the camera’s electrical current). I combined the images, total exposure of 38 minutes, and made this astrophoto:

[The classic barred spiral galaxy NGC7479, in a photo I took during the night of Sept. 6-7, 2010, at Lakeside, Tooele County]

Only later, when I researched NGC7479, did I realize it was the farthest object I ever deliberately photographed. (Sometimes extremely distant galaxies show up in the background of astrophotos, just tiny smudges, which reside far, farther away.) According to NASA’s Goddard Space flight Center, based on data gathered by the Galaxy Evolution Explorer telescope satellite, NGC7479 is 28.88 megaparsecs from Earth.
To make sense of that requires some math. A megaparsec is 1 million parsecs. A parsec is a ridiculous unit of measurement. It’s the distance away that a star must be (if it were stationary, which stars aren’t), in order for its positions to appear separated by one arc-second when seen from opposite sides of Earth’s orbit. What is an arc-second? For those of a technical turn of mind, the night sky from one horizon to the apex is 90 degrees; each degree is 60 arc-minutes; each arc-minute is 60 arc-seconds. Let’s just say an arc-second is a teeny distance.
Using geometry, scientists calculate that a star one parsec away would be 3.258 light-years from Earth. But there are no stars that close. The nearest, Proxima Centauri, is 4.22 light-years from our planet. See what I mean about the absurdity of citing parsecs and megaparsecs? Yet astronomers persist in it.
An on-line converter that changes megaparsecs into light-years gives the answer. Galaxy NGC7479 is 94.19 million light-years away.
The photons that stream from it at the speed of light left those billions of stars 94.19 million years ago.
Earth’s equator is about 24,902 miles long. A good, fast cruising speed for an airliner is 600 miles an hour. At that rate, assuming it was refueled in midair without slowing, it could circle the world at the equator in around 45 hours, 15 minutes. Imagine watching oceans and an occasional jungle pass beneath your airplane for more than 45 hours.
Starlight radiates through space at 186,000 miles per second. It covers the distance represented by Earth’s equator in 0.13 seconds. In one second, light travels about seven times the equator’s length.
So for more than 94 million years, photons traveled at that unimaginable speed, through empty space, to at last impact my telescope.
What was Utah like back when the light left their stars? By email I asked one of the state’s greatest scientists, Jim Kirkland, the state paleontologist.
Ninety-four million years ago was the time of the deposition of what is called the Dakota Formation, he wrote back. A great western interior seaway was just beginning to encroach into Utah from the east.
“Much of the Colorado Plateau (Utah’s red rock country) was a lowland coast, with barrier islands and estuaries along the coast sheltering vast cypress swamps with more inland better drained areas supporting poplar and laurel forests,” he said.
Along the line of the Wasatch Front, the Sevier Mountains were rising, with alluvial fans on the seaward side. “To the west, piggyback basins were formed on the uplifted terrain, constraining rivers that drained to the north-northeast.
“In the seas, diversity of shellfish included beautiful chambered ammonites and inoceramid clams that could have supported a fine pearl industry, if there were beings to appreciate these natural treasures. Fish and sharks swam this sea in large numbers as did the plesiosaurs and immense pliosaurs that hunted them and each other.”
Then there were the land-going dinosaurs. He continued:
“The coasts served as open migration corridors for advanced iguanodonts, bipedal herbivores similar to Eolambia, so abundant a few million years earlier. Armored nodosaurid ankylosaurs also frequented these coasts often enough that their carcasses were often swept out to sea.
“The small ancestors of the horned dinosaurs were rare components of the more upland environments. Small, lightly-built bipedal herbivores of a variety of types were in turn pursued by small raptorial dromaeosaurs, troodontids, oviraptosaurids, and primitive ornithomimids among others.”
Kirkland added that other small meat-eaters took advantage of the seasonal migrations of yard-long, armor-scaled Lepidotes, heading up the rivers each year
“Then again, everything was fair game to the early tyrannosaurids, which had so recently taken over the role of crown predator across western North America.”
Imagine all that has happened since then. Considered in that light, we get some notion of the distance of that lovely galaxy.
Further perspective: the Goddard Space Flight Center lists NGC7479 in its “Nearby Galaxy Survey.”
It is more than 39 times farther away that the looming great galaxy in Andromeda, M31, which is heading toward a collision with our Milky Way galaxy; M31’s center is only 2.4 million light-years off. Still, NGC7479 is a lot closer than many. In 2008, an international team of astronomers announced they had used Japan’s Subaru Telescope on Mauna Kea, Hawaii, to examine 80 “newborn galaxies” 12.5 billion light-years away.

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