Greene's Creationism Truth Filter
 

SN1987A and The Antiquity of the Universe,
by Todd Greene

See also:
The Imminent Demise of Evolution: The Longest Running Falsehood in Creationism
by Glenn R. Morton

Here's something I want you to actually see, because sometimes a picture is worth more than thousands of words. Why is it that we can really say that it is a fact that the stellar explosion SN1987A shows that the universe has been around for at least 168,000 years (which is at least 158,000 years too long for the literalistic young earth/young universe interpretation of the Bible)?

From Hubble Reveals Structure Of Supernova 1987a Explosion Debris is the following image of the SN1987A system that we are talking about:

SN1987A and gas rings

The SN1987A explosion is in the center of the bright yellow ring. The bright yellow ring itself is the primary gas ring. The two fainter gas rings are larger and offset from SN1987A, like the top and bottom of an hourglass shape. (See Hubble Space Telescope Images - Novae and Supernovae for lots of links to information regarding SN1987A, especially regarding the primary ring.)

As you can see for yourself, the distance of SN1987A is known by direct observation. The distance is calculated by a straighforward trigonometric calculation.

Before I step you through the calculation, I want to help you understand the meaning of how this is done with a parallel example. If you walk out of the front door of your house and just step off your porch, then turn around and look at your house, it looms large in front of you. However, if you walk down the street a couple of hundred feet, then turn around and look at your house, it's apparent size is not nearly so large. Indeed, if you hold up your index finger about a foot in front of your eyes, then your house (in the background behind your finger) will appear shorter than your finger. This "apparent size from a distance" is called the angular size. The farther you walk from your house, then the angular size of your house will continue to shrink. Interestingly, if you know the actual height of your house, and from your position at a distance from the house you can measure the angle between the line from your eye to the bottom of your house and the line from your eye to the top of your house, then using a simple trigonometric equation you can simply calculate the distance to your house without actually measuring it off with a tape ruler. This is exactly the same kind of thing that is done with SN1987A. (See Angular Size or Angular Size Calculator for a more detailed discussion of what this is.)

After the progenitor star (known as Sk -69 202; the Sk means Nick Sanduleak catalogued the star) exploded, astronomers measured the time it took for the energy to travel from the star to the primary ring that is around the star. (The ring is quite large, much larger than the "ring" that Neptune makes in its orbit around our own sun.) From this, astronomers determined the actual "height" of the ring from the star. Second, they already knew the angular size of the ring against the sky (as measured through telescopes, and measured most precisely with the Hubble Space Telescope).

So now here are the steps in carrying out the calculation:

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)

I have made a diagram of this here:

Trigonometric Diagram of SN1987A and Earth
Trigonometric Diagram of SN1987A and Earth

Now let's plug everything in:

  1. radius = 6.23 x 1012 km = 0.658 light-years [1]
  2. angle = 0.808 arcseconds = 0.000224 degrees [1]
  3. distance = 0.658 ly ÷ tan(0.000224)
  4. distance = 0.658 ly ÷ 0.00000392
  5. distance = 168,000 light-years

Note that taking the measurement error limits into account makes this value 168,000 light-years ± 3.5%.

For reference:
    c (lightspeed) = 299,792.5 kilometers per second
    1 arcsecond = 1/3600°
    1 parsec = 3.26 light-years
    1 light-year ~ 9.46 x 1012 km
    1 light-year ~ 5.88 x 10^12 miles

[1] New Distance Determination to the LMC
     http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1998MmSAI..69..225P

The "height" (radius) of the primary gas ring around SN1987A is based on the observed time it took for the energy from the explosion to hit the ring (travelling at the speed of light), which was 0.658 years (i.e., almost two-thirds of a year). Indeed, my simple diagram of the geometry is not completely realistic, because the primary gas ring is not "flat on" perpendicular to the earth. However, rotate that ring around any way you please, and there are exactly two geometric points on the ring which represent a right triangle with the three vertexes represented by the SN1987A progenitor star, either point on the ring, and the earth, with the star and the ring point being the "height" side of the triangle and the star and the earth being the "base" side of the triangle. In actuality, the ring is tipped with respect to the earth, which means that with respect to the earth there is a "leading edge" (the closer half) and a "trailing edge" (the farther half). Because of this fact, what astronomers observed was the point on the ring closest to the earth lighting up

He who speaks the truth gives honest evidence....
  — Proverbs 12.17

The heavens are telling the glory of God;
and the firmament proclaims his handiwork.
Day to day pours forth speech,
and night to night declares knowledge.
There is no speech, nor are there words;
their voice is not heard;
yet their voice goes out through all the earth,
and their words to the end of the world.
  — Psalm 19.1-4a

The heart of the discerning acquires knowledge;
the ears of the wise seek it out.
  — Proverbs 18.15

first (from the explosion energy) and then the rest of the gas ring progressively "light up" from the closest point to the farthest point travelling around both sides of the ring. This whole situation is described in The SN1987A Circumstellar Ring and the Distance to the Large Magellanic Cloud (A Homework Problem) by astronomer Richard McCray. Dr. McCray also has extensive discussion about the SN1987A system in Supernova 1987A.)

As I have pointed out previously, SN1987A is in the Large Magellanic Cloud galaxy, which is the second closest galaxy to the earth. There are millions of other galaxies in the universe. So 168,000 years simply represents a very small lower limit. In other words, the universe must be much, much older than 168,000 years, because astronomers can literally observe events like SN1987A in these other far more distant galaxies, events that correspondingly have taken place much farther in the distant past. What makes SN1987A such a beautiful example is the presence of the primary ring, which allows a "reverse parallax" kind of direct calculation of the distance, as shown above.

The universe itself shows us that it has been around far longer than a miniscule 6,000 or 10,000 years. We know this to be a truth about the universe because we literally observe these events from the distant past. Thus, when you hear it said that it is a fact that the universe is ancient, this is genuinely just as factual as saying that the earth revolves around the sun. What this means is that Christians who believe in biblical inerrancy need to sit up and take this truth about creation seriously, and then proceed to work on their biblical hermeneutics accordingly. This is what truth-seeking is all about.

Originally written: 3/16/2000.
2nd revision: 9/14/2000.
This revision: 10/6/2007

From:
http://singularity.astro.uiuc.edu/projects/mcnews/newsletter18.html

Conference Proceedings

New Distance Determination to the LMC

Nino Panagia (1, 2)

  1. Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA.
  2. On assignment from the Space Science Department of ESA.

Using the new reductions of the IUE light curves by Sonneborn et al. (1997) and an extensive set of HST images of SN 1987A we have repeated and improved Panagia et al.'s (1991) analysis to obtain a better determination of the distance to the supernova.

In this way we have derived an absolute size of the ring R_abs = (6.23 ± 0.08) × 1017 cm and an angular size R" = 808 ± 17 mas, which give a distance to the supernova d(SN1987A) = 51.4 ± 1.2 kpc and a distance modulus m-M(SN1987A) = 18.55 ± 0.05. Allowing for a displacement of SN 1987A position relative to the LMC center, the distance to the barycenter of the Large Magellanic Cloud is also estimated to be d(LMC) = 52.0 ± 1.3 kpc, which corresponds to a distance modulus of m-M(LMC) = 18.58 ± 0.05.

Revising accordingly the zero point of the Cepheid distance scale, and using the SNIa measured by Sandage and collaborators, one finds a value of the Hubble constant H_0 = 60 ± 6 km/s/Mpc.

Invited Talk at the Workshop "Views on Distance Indicators", Sant'Agata sui Due Golfi, Italy, 3-6 September, 1997, ed. F. Caputo, Mem. S.A.It., in press.