STARRY NIGHTS
by Gary Boyle
Back to the index
May 30, 2003
HOW FAR IS FAR
One of the first questions people often ask when looking at my telescope is “how far can you see with it”? My reply is, “as far as the night and equipment will take you”. When viewing celestial objects, distance is an obvious factor. Telescopes are specially designed instruments to magnify distant objects. Gathering faint light with lenses or mirrors, these photons passes through interchangeable eyepieces, thus increasing or decreasing magnification, much like a microscope.
Larger telescopes gathers more light and help reveal delicate detail than would an instrument of lesser size. Blend in high thin cirrus cloud, turbulent winds in our upper atmosphere and depending from where you observe – light pollution, you will or might not see illusive objects. A couple of examples are the birthplaces of stars -a nebula, or a remote galaxy like our own harboring over 100 billion stars. Obviously the fainter and more distant the subject, the harder they are to observe. But to answer your question your telescope of binoculars for that matter can catch objects anywhere from light seconds to million of light years from us.
Noticed that I did not use the word kilometer. When dealing with vast stellar distances - standard Earth measurements are too cumbersome to use. Case in point. The closest major galaxy beyond our Milky Way Galaxy is called the Andromeda galaxyand lies a mere 2,900,000,000,000,000,000 kilometers from us. This is extremely large and confusing number to use. Dropping a few zeroes makes a huge difference.
The speed of light travels at 300,000 kilometers per second or seven and a half times around the world in the blink of an eye. A light-year is the distance travelled by a photon of light in one Earth year. Doing the math we calculate over thirty-one and a half million seconds in a year. So we come close to ten trillion kilometers or six trillion miles. We can now state the Andromeda galaxy is 2.9 million ly away. Our own solar system’s planets are relatively close. At such a cosmic stone’s throw we refer to their distances in light minutes. Our moon for instance is 1.25 light seconds away, the sun 8.5 light minutes and the farthest planet - Pluto in twenty minutes shy of six light hours.
The night sky is gazed upon in past tense, down the road of the cosmic highway. So how far down this road do these object lie? Let’s set up a scale to help bring these distances into perspective. First keep in mind an important standard of measure astronomers use when relating to objects in our solar system is the ‘astronomical unit’. Similar to using a ruler to measure something, the astronomical unit is the average distance in space between the Sun and Earth, close to 150 million kilometers or 93 million miles.
There are 63,072 astronomical units in one light year. By coincidence a mile equals 63,360 inches - pretty close to a one to one ratio. So in our model, if you placed a dime on the ground to represent the Sun’s position and not size, our world would be one inch away from it. Mercury and Venus are closer to the Sun, so place them .4 and .7 inches respectively from the dime. Moving past our planet in order, Mars is 1.5 inches, Jupiter at 5.2, Saturn at 9.5, Uranus at 19 inches, Neptune at about 30 inches and Pluto would be almost 40 inches or one metre from the dime.
At this scale the closest star from the Sun named Proxima Centarus would be 4.3 miles down the road as its true distance in space is 4.3 light years. Situated low in the north west sky, the star Capella is the brightest member in the constellation Auriga, 42 light years from us. Mark it 42 miles on your scale. The famous seven Big Dipper stars would be placed 79 to 138 miles away (between the Ontario/Quebec border and Montreal)
Polaris, our north star sits at the 450 miles mark around Sault Ste. Marie and the closest nebula situated in Orion (M42) is 1,500 light years away in space. That puts it on your scale around Winnipeg.
Every star you see at night including star clusters and nebulae belong to our Milky Way. If a grain of sand represented a star, a children's sandbox would equal the population of our galaxy, an estimated 100 billion stars. Other galaxies like ours are situated tens of millions of lights years away and scattered about the universe. Because of their great distances from us, they are faint and require a moderate size telescope as well as dark moonless country skies.
There are literally millions of galaxies other than ours. So you can see, we are merely a teardrop in the ocean of the universe. Major observatories view quasars lying at mind-boggling distances. Some of these are an astounding 15 billion light-years, practically at the beginning of time itself.
