Astronomers Find Sun's Twin

mroch writes "Space.com is reporting that astronomers may have found a solar twin -- a star almost exactly like our own Sun. Interesting tidbits from the article include: "The star, 18 Scorpii, sits about 47.5 light-years away in the constellation Scorpio, and has long-been suspected of being Sun-like. [...] The star burns slightly hotter than the Sun, at 5,789 degrees Kelvin compared to 5,777 degrees. It appears to rotate slightly faster than the Sun, taking 23 days to complete a rotation rather than the Sun's 25." It boggles my mind to think that we can measure temperature that exactly from 279,000,000,000,000 miles away, and that they are complaining over a 12-degree difference."

Comments

Measuring temperature at great distance

[Frans Faase]

Distance actually does not matter with respect to the method used to measure the temperature, as long as you have enough light, and there is no disturbing medium in between. Both conditions seems to be met.

Measuring a star's temperature.

[DjReagan]

IIRC, the temperature is measured by the colour of the sun. That doesn't change the further away you get, so its just as accurate over long distances as short. However, there is the problem of dopler shift if the stars are moving away/toward each other.

Re:Measuring a star's temperature.

[Dr. GeneMachine]

Doppler shift should not be a problem, you can always determine the shift rate from the known frequency of certain absorption lines in the spectrum and reference your spectrum to those lines.

Re:They use spectrometry to measure the heat

[ottawanker]

Actually, 12 a degree difference in Kelvin is the same as a 12 degree difference in Celcius.

Really, you shouldn't use the word 'degree' with the work 'Kelvin' as in the case used in the Story. It's preferable to write simply 5789 Kelvin.

Re:Degrees Kelvin, not Kelvin

[ottawanker]

From The U.S. Metric Association

The kelvin (K) temperature scale is an extension of the degree Celsius scale down to absolute zero, a hypothetical temperature characterized by a complete absence of heat energy. Temperatures on this scale are called kelvins, NOT degrees kelvin, kelvin is not capitalized, and the symbol (capital K) stands alone with no degree symbol. [In 1967 the new official name and symbol for "kelvin" were set by the 13th General Conference on Weights and Measures (CGPM).]

50 closest, closest matches to the sun

[nimblebrain]

I like David Nash's list of 50 nearby sunlike stars within 50 light years.

18 Scorpii is on there, as is the infamous Tau Ceti. 18 Scorpii was one of the four closest matches.

Re:I don't believe it, how can they possibly know?

[PaSTE]

Astronomers look at the spectrum of the star--the relative intensities of each wavelength of light produced by the star's heat. Assuming the star is a black-body radiator (which isn't totally true, but pretty darn close), using first principles you can solve for the temperature of such and object as a function of the peak wavelength of light radiated. See "Thermal Physics" by C. Kittel and H. Kroemer for a better discussion.

Also, single wavelength filters (like your green sheet of plastic) aren't a natural byproduct of nature, and wouldn't be found between here and the aformentioned star. What would would find, however, is interstellar dust, or clouds of hydrogen, helium, lithium, and other light elements. When the light passes through these clouds, certain frequencies of light are absorbed, and certian frequencies are flouresced, but these frequencies are predictable, and the overall shape (and especially the peak) of the spectrum is not changed beyond recognition. "Introduction to Quantum Mechanics" by D. Griffiths and "Introduction to Astronomy and Astrophysics" by Zeilik and Gregory should help you out with spectra and spectral lines.