The Speed of Light
Astronomers use several funny sounding terms to describe astronomical distance.
Three of these terms are:
AU- Astronomical Unit- which is the average distance between the center of the Earth and the center of the Sun. This is described as “1 AU”…. and Saturn’s distance can be described as 9.5 AU.
Red Shift- spectra of nearby stellar objects are used to measure distance based on what is called a “Z” factor. Discovered by Edmund Hubble- the red shift is proportional to distance.
Light Years- the distance light travels in ONE year– light travels at 186,000 PER SECOND….. or 11,160,000 MILES in ONE MINUTE!
Why do they use these methods and others to describe distance? Because the Universe is so vast that if they used kilometers or miles the numbers would be HUGE and incomprehensible! So let’s review several stellar objects and the TIME it takes for light to reach us from those objects. This will give you a better understanding of just how far away objects are in the sky that we can observe with our telescopes……… or just by looking up at night.
| Object Name | Time for the light to reach usThe Speed of Light |
| The Moon- | 1.3 seconds |
| The Sun | 8 minutes average |
| Jupiter | 45 minutes average |
| Pluto | 5.5 hours average |
| Alpha Centauri nearest star | 4.3 YEARS |
| Sirius brightest star | 9 YEARS |
| Orion Nebula M42 | 1500 YEARS |
| Far side of Milky Way Galaxy | 100,000 YEARS ! |
| Andromeda Galaxy M31 | 2.5 MILLION YEARS!!!! |
One (1) Light Year is about 5.8 Trillion miles.
This illustrates the vast distances of even the nearby stellar neighborhood. When we view the Andromeda Galaxy in our telescopes we are seeing it AS IT WAS 2.5 million years ago! So our telescopes become “time machines” for viewing the past!
The latest estimates for the WIDTH of the Universe is about 156 BILLION LIGHT YEARS WIDE!
So get outside tonight and see What’s Up!………… in the past! with your time machine- a telescope or binoculars. 🙂
Clear skies!
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