Is there any uppermost temperature? Is it possible to measure the temperature in the core of a star?

Temperature has a lower limit, but not an upper least in theory. In the mid-1800s, Lord Kelvin created an absolute temperature scale whereas the lowest temperature possible is 0 K. He came up with this theory using Carnot's theory which is the foundation to the fundamental laws of thermodynamics. To learn more about Carnot's theory, you can read about it in any fundamental physics or thermodynamics book.

Anyways, Kelvin's 0 K has withstood the test of time as the lower limit. Not a single scientist nor anything in nature has been able to reach a temperature of 0 K or less. As for an upper limit, scientists are not willing to make a guess until more about the universe is known.

Some of the highest temperatures in the universe have been found in the cores of stars. The sun's core is close to 14 million K. The core temperature of a star about to go supernova can reach several billion K. So how do scientists figure out what the core temperature is?

Since stars are so far away, it's obvious that we can't just go stick a huge thermometer in them. Instead, astronomers analyze the light that a star produces. Astronomers not only analyze the visible part of the spectrum, they analyze all of light spectrum, from the electromagnetic waves to x-rays. They do this through something called "spectroscopy". Spectrographs are optical instruments that astronomers attach to telescopes to disperse the light from a star into several bands and lines. These bands and lines are then analyzed to determine the temperature of each of the star's layers.

The bands and lines have a wide range of widths and colors. The widths and colors act like a fingerprint of the star. Depending on the widths of certain colors or the combinations of widths, astronomers can determine which elements are contained within that star. Once they determine that, they are able to determine which nuclear reactions are going on within the star's core. By determining the nuclear reactions, they then estimate the amount of thermal energy that is being given off at the core, thus providing them with the core's temperature.

Submitted by Morten (Norway)
(January 9, 1998)

Last modified May 10, 2010 by Randy Russell.

You might also be interested in:

What are the retrograde motions of planets in the sky?

It depends on what kind of motion you are talking about. When seen from the north pole of the celestial sphere all planets orbit around the Sun in a counter-clockwise or direct path. Most planets also...more

How do Astronauts Live in Space?

Almost everyone has a question or two about living in space. What do astronauts do in space? How do they do everyday things like eat, sleep and go to the bathroom? Well, this is our attempt to answer...more

How far is the Earth from the Sun, the Moon and all the other planets? How far are all of the planets from the Sun? Do you know of a software that tracks the planets in real-time?

There is a really neat internet program called Solar System Live that shows the position of all of the planets and the Sun for any given day. If you go to that page, you'll see an image similar to the...more

Is it really true that man never really walked on the Moon?

The picture of the American Flag (the one put there by the Apollo astronauts) is waving (or straight out) in the wind. How could that be possible if there is no atmosphere on the Moon? Was it some sort...more

How many planets orbit the sun?

I was wondering if there is a new planet? Are there planets (a tenth planet?) after Pluto belonging to our solar system? What are the names of the new planets discovered in the solar system? Are there...more

According to Stephen Hawking, any object with an energy which equals Plank's energy has to become a black hole.

If that is so, the energy released during the Big Bang must have created many such black holes. Therefore most of the Energy of the Big bang must have disappeared in that form. Then how did the Universe...more

Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA