Astronomy Rough Notes –Waves, Types, Properties, Energy
BRING:
Rope
~ wave generator, speaker, wires
Oscope
Metal rod
Blow torch, flint
DISCLAIMER: These notes do NOT cover everything you need to know. You may need to look up some item or concept online or in a text. Test questions are not exact copies of the OBJECTIVES but if you know the OBJECTIVES thoroughly, you should do well on the exams.
HANDOUTS: None
OBJECTIVES
What is a wave?
Define, write the symbol for, and write the units for each of the following: wavelength, frequency, and speed (velocity). Define and give the abbreviation of an Ångstrom. Review the definitions and abbreviations of the metric prefixes giga, mega, kilo, centi, milli, micro, and nano so that you can define, know the meaning of and give the symbol for each.
For a sound wave, which wave property corresponds to pitch?
From the demonstration with the speaker, wave generator, and oscilloscope: Use the terms longer, shorter, higher, and lower to compare a high pitch sound to a low pitch sound in terms of their frequency and wavelength.
Is a blue flame hotter or cooler than the red rod it is heating?
Use the terms higher, lower, greater, lesser, longer and shorter to compare the light from the red rod to the light from the blue flame in terms of their energy, frequency, wavelength, and temperature.
State the colors of the visible spectrum in order from coolest to hottest.
If you see a red star and a blue star, what can you conclude?
What color do astronomers and others use to portray high intensity? Low intensity?
State the approximate wavelengths of red and violet (blue) light in both Ångstroms and nm.
If you detect an astronomical object emitting short wavelengths, what can you conclude?
What does the color of a star or hot dense object tell you?
Name the seven types of EM radiation in order from lowest to highest f, from longest to shortest wavelength, from lowest to highest energy.
Watch the video “Infrared: More than Your Eyes Can See” (link near end of notes). State one advantage that IR astronomers have. State one disadvantage.
Wave
Operating definition: Periodically repeating disturbance
Ex: Ripples in a pond, Guitar string, Sound, Light
Show wave on rope
Some wave properties (How to describe waves)
Velocity (speed)
Define: How fast the wave moves, Distance/time
Symbol: v
Units: m/s, mi/h (mph), ft/s, ...
Example: Speed of light in space = 186 000 mi/s
Speed of sound in air =1100 ft/s
Wavelength
Define: Distance between similar points on a wave in the direction of travel
Credit: http://www.qrg.northwestern.edu/projects/vss/docs/media/Communications/wavelength.gif
Symbol: l
Units: m, mi, ft..., nm, mm, Å (1 Å = 10-10m)
Example: Red light l = 700 nm = 7000 Å
Blue (violet) l = 400 nm = 4000 Å
Middle C l = ~1 m
Frequency
Define: Number of oscillations per second
Symbol: f
Units: Hertz (Hz), 1 Hz = 1 cps = 1 cycle per second
Example: 88.5 MHz
Middle C f ~ 330 Hz
For sound: frequency « pitch (higher f means higher pitch, lower f means lower pitch)
Energy
Define: Ability to make something happen
See http://www.flyingturtle.org/energy/definition.html
Example describing waves, frequency, wavelength using the words higher, lower, longer, shorter
Demo: Sound and O-scope
In-class exercise: Write a sentence or two using the words higher, lower, longer, shorter to compare a higher pitch sound to a lower pitch sound in terms of their frequency and wavelength.
Quick hearing check/ sound stories
Which star is hotter: reddish or bluish?
Demo – Heat rod with torch
Observations:
Blue flame
As rod heated: Red → Or → Yel/Or
As rod cooled: Yel/Or → Or → Red → “warm”
Conclusions:
Blue is hot, red is cooler
Ex: star gazing – reddish star is cooler than a blue white star
Tie to molecular and atomic vibrations with temperature
Higher energy means higher temperature means higher f means shorter λ
In-class exercise: Write a sentence or two using the words higher, lower, longer, shorter to compare a reddish star to a bluish star in terms of their energy, temperature, frequency and wavelength.
Portrayal of intensity - red is intense, blue is less so
Photos in art and in astronomy
So read captions of pictures to find out if the wavelengths are visible or not.
Electromagnetic (EM) Spectrum
Expand ROY G. BIV
Part of the above from http://library.thinkquest.org/10380/advanced.shtml
Here is a nice piece on IR radiation:
“InfraRed: More than Your Eyes Can See” http://www.youtube.com/watch?v=2--0q0XlQJ0
Sometimes EM spectrum is displayed the opposite way:
From http://library.tedankara.k12.tr/chemistry/vol1/period/trans43.htm
Note: All these waves travel at the same speed, namely, the speed of light.
Homework:
Make a flash card for each objective.
View the infrared link on YouTube. http://www.youtube.com/watch?v=2--0q0XlQJ0
Work the take home quiz on EM waves. Hand it in at next lecture.
Work the tutorial about EM Spectrum (will be emailed to you). Do not hand in this one.
Revised 5 January 2015