UNIVERSE

PART II: Spectral Analysis

POWERPOINT “Spectral Analysis” QUIZ #2 – Due Tuesday, September 15

• 1) What is a spectroscope?• 2) What is the difference between an absorption line and an

emission line?• 3) How are these spectral lines used to identify elements

‘burning’ in the star?• 4) Compare the Doppler effect with sound to the Doppler

effect with light.• 5) How do scientists know that stars are moving?• 6) What are the two most abundant elements in the

universe?

Last time – talked about telescopesWhat else do scientists use?

• INSTRUMENT USED TO STUDY LIGHT?

Spectroscopes

• Spectroscopes break down the light emitted or absorbed by elements into specific lines of color.

• Every element has a "fingerprint" of its own that can be used to identify it.

• These fingerprints are generally produced when electrons gain or lose energy– Different energies produce different colored lines

• Spectrum - a display of electromagnetic radiation as a function of wavelength.

• Isaac Newton (1671) reported his experiment of decomposing the white sunlight into colors using a prism.

ROYGBV

• Spectroscopy is a method of analyzing the properties of matter from their electromagnetic interactions

• Every different type of atom or molecule gives off light at its own unique set of frequencies

• Astronomers can look for gas containing a particular atom or molecule by tuning the telescope to one of the gas's characteristic frequencies. – For example, carbon monoxide (CO) has a spectral

line at 115 Gigahertz (or awavelength of 2.7 mm).

• Each element has several prominent, and many lesser, emission lines in a characteristic pattern. – Sodium, for example, has two prominent yellow

lines (the so-called D lines) at 589.0 and 589.6 nm -- any sample that contains sodium (such as table salt) can be easily recognized using this pair of lines.

• A spectral line is like a fingerprint that can be used to identify the atoms, elements or molecules present in a star,galaxy or cloud of interstellar gas.

HYDROGEN

ACTIVITY

• http://www.colorado.edu/physics/2000/quantumzone/index.html

CAN WE TELL IF A STAR IS MOVING????

• DOPPLER EFFECT

• http://www.animations.physics.unsw.edu.au/jw/doppler.htm

• http://www.lon-capa.org/~mmp/applist/doppler/d.htm

SOME INTERESTING FEATURES

• Some of the absorption (or emission) lines were shifted from where we see them in the lab.

• WHY?

RED SHIFT BLUE SHIFT

DOPPLER EFFECT

• Recognized with sound: relative motion of the source causes the wavelength of the sound waves to be decreased ahead of the source and stretched out behind the source

Animation

• http://www.lon-capa.org/~mmp/applist/doppler/d.htm

• Also seen in light: it is not the pitch but the color (that is, the wavelength) that is shifted by the motion of the source

• Red Shift – wavelengths are shifted to the longer (red end) of the spectrum. Indicates that the object is moving away from the observer

• Blue Shift – wavelengths are shifted to the shorter (blue end) of the spectrum. Indicates that the object is moving towards the observer

Composition of Stars

• Hydrogen and Helium with minor amounts of Iron, Sodium, and Calcium

What are Spectral Lines

• https://www.youtube.com/watch?v=UnH3nsk-Ibs

• https://www.youtube.com/watch?v=TbFehcC4MHc

• https://www.youtube.com/watch?v=fPt0jXHwqUw