Using only triginometry we can use Supernova 1987A to PROVE that the universe is AT LEAST 168,000 years old thereby eliminating once and for all, the notion that the earth is less than 10,000 years old
The importance of Supernova 1987A is that it doesn't even use the speed of light to determine that the closest supernova (explosion of a star) was approximately 168,000 light years away.
Explanation of the technique used
When supernova SN1987A exploded, a fair amount of ultraviolet light was given off in addition to the usual, visible light. About a year after the explosion, the light struck a ring of gas some distance from the star, illuminating different parts of it at different times. "Its absolute diameter was determined based on the timing of ultraviolet spectral lines, where observed light curves are fitted to models. The angular size on the sky is known from Hubble telescope measurements." (Ron Ebert, Internet, 5/20/98). (The angular size is roughly how big something appears to you. I. e., your small fingernail, held at arm's length, has about the same angular size as the moon viewed without instruments.) It turned out that this ring of gas is titled about 43 degrees to our view. Knowing the actual diameter and the angular diameter, the distance is easily calculated using a simple, trigonometric formula, and was done with an error of less than 5%.
Distance equals the actual diameter of the object divided by twice the tangent of half the angular size
No matter how a perfect circle is viewed in space, the longest line across it from our viewpoint will give the true, angular diameter. Knowing the real size of an object (say, in miles) and how large it appears (in degrees), one can calculate the distance. The distance formula falls right out of the definition for the tangent function. Take the moon, whose diameter is 2160 miles, whose angular size is 0.5 degrees. That yields a distance of 248,000 miles, which is quite decent. (If you are not familiar with trigonometry just skip this.)
Application of the technique to SN1987A
Think of a right triangle.
* The line from SN1987A to earth (distance) is the base.
* A line from SN1987A to the ring (the radius of the ring) is the height.
* The line from the ring to earth is the hypotenuse.
* The angle between the base and the hypotenuse is half the angular size of the ring
* trig formula: base = radius ÷ tan(angle)
a. radius = 6.23 x 1012 km = 0.658 light-years 
b. angle = 0.808 arcseconds = 0.000224 degrees 
c. distance = 0.658 ly ÷ tan(0.000224)
d. distance = 0.658 ly ÷ 0.00000392
e. distance = 168,000 light-years
This is significant because Creationists claim that the earth and the heavens are no older than 6000 years old and therefore, too young for evolution to have taken place. They explain away the real age of the universe (approximately 13 BILLION years old by saying that the speed of light ( the constant C in astronomy) was much faster sometime in the last 6000 years (and therefore, not a constant) so the things we see that we THINK are millions of light years away are actually only 6000 light years away - at most.
I am not making this up. I will show you their articles attesting to the same later on.
Many creationists would have you believe that the speed of light was once very high and has been slowing down ever since. The motivation for this reasoning is to keep the age of the universe at about 6000 years while accounting for the fact that we can see the distant stars. If there is any truth to that claim, then the light we now see from SN1987A must have been traveling considerably faster when it left the vicinity of that supernova. That means our telescopes today would see things happening there in slow motion! As it so happened, by studying changes in the light levels, astronomers were able to calculate the half-lives of the cobalt-56 and cobalt-57 created in the aftermath of that supernova explosion. Far from exhibiting a slower decay rate, their decay rates matched the cobalt-56 and cobalt-57 decay rates measured in our laboratories. Therefore, the light leaving the vicinity of SN1987A was traveling at its normal speed, and that means we are seeing things almost 200,000 years ago!
Here are a number of articles that confirm the above explaining how Supernova 1987A can be used to PROVE the universe is at least 168,000 years old.
SN1987A and The Antiquity of the Universe
Proof of Distance to SN1987A
SN1987A - A Technical Explanation
Everything you could possibly want to know about SN1987A