ModPhy Example Reports: Solar Spectra by Geoff Matthews

The Monthly Sun

Science

UT Physicists Debunk “Angry Sun-God” Theory
Claim “the sun is a mass of incandescent gas”

Marchiali
Dissociated Press

A group of University of Texas physics students (henceforth referred to as “the physicists”) recently conducted an experiment to determine the temperature and chemical composition of the sun. They also cooked hotdogs with a high powered solar telescope.

By determining the chemical properties of the sun, the physicists challenge the long held view that the sun is an imprisoned deity. Current theories state that such a sun god would be much like a human, except with powerful magical abilities for lighting the daytime sky.

Reading Between the Lines

The UT physicists have modified a technique developed almost two hundred years ago to calibrate lenses (In Line with Fraunhofer, November 96). Using special equipment, they split the sun’s light into its component wavelengths, as when light passes through a prism. While the sun emits light of all colors, some are much dimmer than others nearby. These dimmed wavelengths, first discovered by Fraunhofer, correspond to colors absorbed by gases in the sun. The physicists also used the separated colors to determine the temperature of the sun.

These two uses for the solar spectra easily adapt to general use in astronomy, allowing astronomers to determine the chemical makeup of the other celestial bodies and possibly help determine their distances from the earth. Many scientists now aim to adapt the technique used at the University of Texas to challenge the theory that stars are lightbulbs in the sky, and that the moon is made of cheese.

Inside This Issue
1	Science: Can the sun-god withstand the evidence?
2	Travelogue: Dante travels on to Purgatory
3	Technology: STI finds no intelligent life on Earth, changes name and sets sights on other worlds
4	Education: New York school uses snipers to motivate students. Warns "The killings will continue until test scores improve."
5	Medicine: Doctors conclude that being born raises one's chance of dying in the next 100 years to nearly 100%.

What Can Light Say About the Sun?

“The brightest wavelength reveals the surface temperature of the sun,” explains Geoff Mathews, one of the physicists who conducted the experiment, “since it follows the blackbody law for the thermal emission of light.”

A “blackbody” is an object that absorbs all the energy that strikes it. The blackbody heats up and emits light itself. At the beginning of this century Max Planck derived a formula to predict the intensity of every wavelength of light as a function of an object’s temperature.

Physicists noticed similarities between the light emitted by the sun and light emitted by blackbodies in laboratories. This led the UT physicists to theorize that the outer layer of the sun emits light because it is heated. The surface of the sun absorbs all the energy emitted by the core and re-emits if like a blackbody. One of the notable features of blackbody radiation is that as an object heats, it emits more and more radiation in the short wavelengths in comparison to the longer ones.

Every IRS agent has noticed this phenomenon as he or she heated a poker – it first glowed red, then yellow and white, and finally blue before being applied to an audited citizen. These citizens can attest to the difference in temperature between blue and red pokers. The color with which a heated object glows indicates the wavelength of highest intensity, which accurately measures the temperature of the object. Objects that glow red have their peak intensity in the infrared but still have visible emissions in the red range. Objects that glow blue have their peak intensity in the ultraviolet but still have significant emissions in the blue range.

An object glows white or yellow when its temperature is between those needed to glow red and blue. While the peak intensity may actually be green, the surrounding colors are strong enough to blend and create a yellow colored glow, like the glow of the sun. In this way, the strongest wavelengths emitted by an object can tell a physicist its temperature.

To exactly determine this peak wavelength, physicists use a technique first noted by Fraunhofer and later perfected by Kirchhoff.

By splitting light from the sun into its component wavelengths, the UT physicists could determine the brightness, or intensity, of these separate wavelengths.

“We found the sun emits most strongly at a wavelength of 460 nanometers, a light blue color,” Mr. Mathews said in his report on the experiment. “From the Planck formulas, we can conclude that the surface temperature of the sun is 6300 Kelvin, or almost 11,000 degrees Farenheit. Since the core would be even hotter, there’s no place a god could live in the sun.”

This graph shows the intensity of each wavelength from 330 nanometers to 800 nanometers. The peak at 460 nanometers clued physicists into the surface temperature of the sun, 6300 Kelvin. Here the “blackbody curve” of an object heated to 6300 Kelvin is imposed on the data.

Silence of the Lambdas

However, just as silence can say as much as a dramatic speech, the wavelengths of light (commonly written as the Greek letter lambda, l) which physicists don’t find can say much about the makeup of the sun. Long ago, people noticed that shining a white light through a prism broke that light into its component wavelengths, or colors. Last century, Kirchhoff noticed that passing the white light through a vapor caused some wavelengths to disappear from the spectrum! He soon learned that different chemical vapors caused different wavelengths to disappear. Scientists determined the chemical makeup of everything from clothes and coins to foods.

Now, the UT physicists have used this same technique to determine the elements in the outer “atmosphere” of the sun. When they saw that the light emissions followed the well studied “blackbody curve,” they also noticed that some wavelengths were quite dimmed. These wavelengths corresponded to several elements that have already been well studied, such as hydrogen, iron, and magnesium.

Mr. Mathews concluded the report by comparing the sun’s chemical composition with the known composition of deities. “We found far more iron, calcium, and magnesium in the sun that we would expect in a sun god. In fact, we wouldn’t expect to detect any absorption lines, since a gaseous sun god is only slightly more feasible than an actor becoming President.”

This graph shows two dips in the intensity, at 393 and 397 nanometers (left and right, respectively). Together, these absorption lines indicate the presence of calcium in the sun’s cool outer gases.

Scientific Debate

Established researchers at other institutions have expressed doubts as to the validity of this research. Most notable among the experiment’s detractors is Dr. Christopher Reinauer, of Illuminati University. He claims that the group’s data has actually been supplied by the sun god himself, in an attempt to keep mortals from fathoming his true nature.

In the raging debate, Mr. Mathews has offered the following defense of his research.

“Our calculated value for the sun’s temperature is consistent with many other related, well established pieces of data. By approximating the earth as a blackbody heated by the sun, we can estimate an average terrestrial temperature of 300 Kelvin. This only slightly varies from the measured average of 290 Kelvin. Other physicists have modeled the sun as a ‘gigantic nuclear furnace, where hydrogen is made into helium at a temperature of millions of degrees.’ Their work predicts a solar surface temperature in the neighborhood of 6000 K. No model explains the data as well as the ‘incandescent gas’ model.”