Stellar Spectroscopy Interactive (132.0K)
Astronomy can be defined as the study of light that reaches us from the heavens. That light carries vast stores of information, if you know how to read it. The spectra of stars give clear, unambiguous clues to their temperatures and atmospheric compositions, among other things. This Interactive shows you how it works: that stars of different temperatures have unique blackbody spectra, and that absorption lines within those spectra disclose the atmospheric elements of the star. Choose the temperature of a star, select some elements for the atmosphere, and the correct spectrum appears.

1			In solar spectrum the dark doublet absorption lines due to this element in the yellow portion of the spectrum are the most obvious dark lines. But in the interactive, when you went to stars twice as hot as our own, these dark lines vanished entirely. What element is this? Need a Hint?
			A)	Hydrogen
			B)	Helium
			C)	Sodium
			D)	Titanium Oxide

With spectroscopy, we have the tool that lets us study the temperatures and compositions of stars far beyond the solar system. In these problems, we will see how the message of starlight is decoded and applied to the starry host. Let's apply it to the prominent winter constellation, Orion.

2			Orion of the winter sky is one of the most prominent and colorful of all star groups. Let's look at the opposite corners from the three stars in a row that mark his belt. Betelguese in his shoulder looks red-orange in color, while Rigel in his knee sparkles blue-white in diamond fire. From this alone we can imply: Need a Hint?
			A)	Betelguese is a huge red giant star.
			B)	Because Rigel is hotter, it is much more luminous that Betelguese.
			C)	Betelguese is about half as hot as our yellow Sun, and Rigel is perhaps twice as hot.
			D)	Betelguese is an old star, while Rigel is much younger.

At different temperatures, some elements are more prominent than others, but as you pull the slider, you notice changes. These changes were used about a century ago to come up with the seven spectral types we now use. How did this begin?

3			What element was most prominent in the type A stars, at about 10,000 degrees, but faded in intensity as you went to cooler star, and thus began the initial alphabetic sequence, now much changed with additional data. Need a Hint?
			A)	Hydrogen
			B)	Helium
			C)	Magnesium
			D)	Titanium Oxide

It is not just atoms that show up in the spectra, and the presence of molecular lines can be especially important in many ways.

4			Which of these is an important visible spectral indicator of the coolest stars, where atoms are colliding gently enough to stick together? Need a Hint?
			A)	Water Vapor
			B)	Carbon Dioxide
			C)	Titanium Oxide
			D)	Methane

We can extend our studies now into the infrared, to objects even cooler than the M stars. Now many elements have a chance to undergo chemical reactions and form compounds, and they too can be used for temperature indicators.

5			Brown dwarfs are "stars that failed", less than 8% of the Sun's mass and unable to ignite hydrogen to helium fusion in their cores. Because they are so cool and red, they are faint and easy to miss, but we now use the infrared spectrum of what simplist hydrocarbon to easily find they are less than 2,500 K hot? Need a Hint?
			A)	Methane
			B)	Octane
			C)	Ethyl Alcohol
			D)	TNT