Astrophoto: The Great Andromeda Galaxy- M31 by Takayuki Yoshida

Article written: 5 Dec , 2006
Updated: 21 Dec , 2015
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Our lives in the early 21st Century can be characterized by many words and phrases. One of them, surely, is our sense of instantaneousness! For the first time in human history, practically any person on the planet can have a live conversation with anyone else using the now ubiquitous cell phone, as one example. Our voices, text messages, pictures and, increasingly, streaming media bounce effortlessly at the speed of light from hand held devices through ground based repeaters to satellite transponders and vice versa. I suspect, our great grandparents would be stupefied by all of this because we have essentially managed to bring the distance between all points on Earth to a practical zero point. Yet, we are surrounded (no, we are engulfed) by circumstances that are in stark contrast to our modern sense of reality. To understand what I am referencing, look up at the sky or take a peek at the accompanying picture.

The majestic image that accompanies this article was produced by Takayuki Yoshida (here’s an English version of his website translated with Babelfish) from a dark site in Yoshinaga, Okayama Prefecture, Japan. The 2.5-hour exposure was produced with a five-inch apochromatic refractor and an 11 mega-pixel astronomical camera. It presents our nearest independent galactic neighbor, the Great Galaxy in the northern constellation of Andromeda, The famous French astronomer and comet hunter, Charles Messier, also designated it as M31 in his catalog of bright, diffuse night sky objects so he would not mistake it as one of his quarry. Even though the image was produced less than a month ago, in November 2006, the view it depicts is actually quite ancient! This is because M31 is extremely remote and light, which moves at about 670 million miles per hour, still required 2.5 million years to cross the gulf that separates us before it reached the astro-photographer’s telescope and CCD camera.

To place this in perspective, consider that the farthest distance between any two points on our planet is about 13,000 miles. Driving an automobile without taking breaks for gasoline, food, sleep or other natural necessities would require about nine days to cover this distance at sixty miles per hour. Of course, the driver would have to eventually contend with one or more oceans and a few mountain chains during the trip, so let’s consider something more realistic and faster like a jet. Commercial aircraft can avoid obstacles caused by terrain and cruise almost ten times quicker than a car on the ground. But even a passenger jet would take approximately twenty-two hours to fly 13,000 miles, non-stop, from departure to arrival. The New Horizon’s probe that’s on its way to study the (recently re-classified dwarf) planet Pluto is one of the fastest man-made objects ever launched from Earth and it’s currently moving through interplanetary space at about 17 miles a second. At that rate, this spacecraft will zip through 13,000 miles in about twelve and a half minutes without even noticing it.

But even the pace of our fastest space mission is like watching fingernails grow compared to the speed that light (and a cell phone call) flows. To a light wave, 13,000 miles is an insignificant hurdle and requires only 70 milliseconds for it to leap over! It’s no wonder we feel so instantly connected to each other with our modern gadgets! Our conversations are traveling at a rapidity we can barely imagine.

However, light does not travel at an infinite speed. Light moves at a rate of about 186,000 miles a second through a vacuum. While this permits a person in New York to have a live chat with someone in China, it has an effect on our view of objects that are located at astronomical distances. For example, our closest natural neighbor in space, the Moon, is about 240,000 miles away, on average. The Apollo spacecraft that carried men to the lunar surface required a three day journey and light needs one and a third (1.3) seconds to do the same thing! The Sun is located even farther away- its rays are in transit for about eight minutes before reaching us. This means we see the sun as it was, not as it is- eight minutes have elapsed since it looked like we now perceive it!

The planet Jupiter is even more distant- it appears to us as it was thirty-five minutes ago. The next nearest star to our planet, Proxima Centauri, is much farther than the Sun- our view of it takes over four years to arrive here. During the summer, the heart of our Galaxy, where the constellation Sagittarius meets Scorpius, can be an inspiring vision but it’s not how it looks today because our view is limited to how it appeared when it was 26,000 years younger!

Although our view of people and objects rooted to the Earth are perceived in real time, the moment our eye wanders above the horizon our sense of reality becomes distorted because distance affects time. The distant objects that appear in the sky are only visible because they are older than the space separating us.

For example, if you were to attend a backyard party where the speed of light slowed to one foot per year, your view of friends and relatives at this gathering would be quite different than you would normally expect. The person standing next to you would immediately look younger and folks a few feet away would have an even more rejuvenated appearance because each foot of distance would act like a fountain of youth- you would see them as they appeared in the past, one year younger for every foot of separation. People just twenty feet away would look, and act, like teenagers while those further back would be babies. Party goers would grow older as they approached! Each foot of reduced distance would pile on the years!

Most likely, no one would be visible standing more than eighty or ninety feet from your position since that would require them to have existed before they were born. So it is with the sky- the stars that fill the firmament can be seen because their age exceeds their distance. There may very well be thousands of new stars, exploded galaxies or other odd objects filling the sky (at this very moment!) but we will not know it until time has passed and their light finally reaches us.

Do you have photos you’d like to share? Post them to the Universe Today astrophotography forum or email them, and we might feature one in Universe Today.

Written by R. Jay GaBany


2 Responses

  1. dasven says

    To place this in perspective, consider that the farthest distance between any two points on our planet is about 13,000 miles. Driving an automobile without taking breaks for gasoline, food, sleep or other natural necessities would require about nine days to cover this distance at sixty miles per hour.

  2. dasven says

    For example, if you were to attend a backyard party where the speed of light slowed to one foot per year, your view of friends and relatives at this gathering would be quite different than you would normally expect..
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