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Spectral Interpretation 101

One of the most powerful tools in the astronomer's shed is the spectrograph. These devices make very high resolution rainbows, and they show us which colours the astro gases have added light to or removed light from. These additions and subtractions tell astronomers what a star is made from, how hot it is and also how the material is moving. Here are a few examples made with an echelle spectrograph, followed by a quick quiz at the end, to see if you've been paying attention.

We start with a normal spectrum.

A Normal Spectrum

[Part of
the solar spectrum]

Told you so. This spectrum of the Sun is a fairly representative example. Its surface temperature is about 5800 K (10500 Fahrenheit or Gas Mark 567), which is cool enough to show off its collection of neutral metal atoms but too warm for molecules to form. In this section of spectrum around the sodium (Na) D lines most of the lines are due to metal atoms in the Sun's atmosphere although there may be small contributions from the Earth's atmosphere, particularly from water. I have identified some of the solar lines giving the wavelength in angstroms (1Å = 10-10m = one ten billionth of a metre), the type of atom using standard chemical abbreviations and the ionisation state where I represents neutral and II means singly ionised.

You've already met the D lines, they are responsible for the orange glow in our street lights. The D is a throw back to the original classification of the solar spectrum by one Joseph Fraunhofer in the early 1800's.

Next: Hot Star Spectrum >>


Daniel Pooley was born in Kent and developed an interest in astronomy at an early age. In the 1980's his family emigated to New Zealand and he kept up his hobby under southern skies (which are superior to northern ones, by the way) all the way to the University of Canterbury, where he eventually completed a PhD on the dynamic aspects of old stars (hence the large amount of science in these pages). Subsequently he returned to dear old Blighty and works at a college in London. As a demonstrator he can occasionally be seen star gazing at the observatory, and is becoming more familiar with our "inverted" skies. Daniel also tinkers with computer stuff and designed the astronomy part of the HSS website.




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Last modified: Sat Oct 20 21:21:47 2007