http://www.astronomynotes.com/light/discretc.gif

Suppose two observers look at the spectrum of a cloud of gas in a laboratory; the first reports seeing emission lines and the second reports absorption lines. Explain.

1) Only the first observer sees the gas against a hot background

2) Only the second observer sees the gas against a hot background.

3) One observer is moving rapidly relative to the other.

4) The atoms in the gas are forming molecules.

http://upload.wikimedia.org/wikipedia/commons/thumb/b/b2/Hydrogen_transitions.svg/2000px-Hydrogen_transitions.svg.png

656 nm486 nm434 nm410 nm

656 nm: red-orange486 nm: blue434 nm: indigo410 nm: violet

http://www.daviddarling.info/images/hydrogen_spectrum.gif

Atoms of different elements have unique spectral lines because each element 1) has atoms of a unique color. 2) has a unique set of neutrons. 3) has a unique set of electron orbits. 4) has unique photons.

http://webmineral.com/help/FlameTest.shtml

Atoms have particular associated spectral lines because 1) electrons have only certain allowed orbits. 2) light consists of waves. 3) light waves can show the Doppler effect. 4) speed of light in a vacuum is a constant.

In the Sun, the transition from level 4 to level 2 of hydrogen produces photons with a wavelength of 486.1nm. In a star twice as hot as the Sun, this transition would produce photons with 1) half that wavelength. 2) the same wavelength. 3) twice that wavelength. 4) four times that wavelength.

Here is the spectrum of a mystery star: Which elements are present?

1. Calcium only2. Calcium and hydrogen3. Magnesium and calcium4. Calcium, hydrogen, and magnesium

Here is the spectrum of a mystery star: Which elements are present?

1. Calcium only2. Calcium and hydrogen3. Magnesium and hydrogen4. Calcium, hydrogen, and magnesium

Decoding Cosmic Spectrahttp://www.pbs.org/wgbh/nova/space/decoding-cosmic-spectra.html

Here is the spectrum of a mystery star: Which elements are present?

1. Calcium, hydrogen, and magnesium2. Calcium and hydrogen3. Magnesium and hydrogen4. All of them

http://abyss.uoregon.edu/~js/hc209/lectures/lec09.html

http://jersey.uoregon.edu/prf/

THE SPECTRAL SEQUENCEClass Spectrum Color Temperature

Oionized and neutral helium, weakened

hydrogenbluish 31,500-49,000 K

B neutral helium, stronger hydrogen blue-white 10,000-31,500 K

A strong hydrogen, ionized metals white 7500-10,000 K

F weaker hydrogen, ionized metals yellowish white 6000-7500 K

Gstill weaker hydrogen,

ionized and neutral metals

yellowish 5300-6000 K

K weak hydrogen, neutral metals orange 3800-5300 K

Mlittle or no hydrogen,

neutral metals, molecules

reddish 2100-3800 K

Lno hydrogen, metallic

hydrides, alkalai metals

red-infrared 1200-2100 K

T methane bands infrared under 1200 K

OBAFGKMLT

http://www.pbs.org/wgbh/nova/programs/ht/qt/3114_06.html

Origins: Decoding Spectra of Light from Distant GalaxiesOrigins Hour 4, Back to the Beginning, Chapter 6