Folks, I'm out today (and tomorrow as well, I expect). Here's what to work on:
Read the pages on spectral classification:
http://www.astrometry.org/starclassification.php
(Note the mnemonic: "Oh be a fine girl/guy, kiss me" to remember: OBAFGKM
If you're up to it, read the wikipedia page:
http://en.wikipedia.org/wiki/Stellar_classification
Next, look into the Hertzsprung-Russell diagram.
http://figshare.com/articles/Hertzprung-Russel_Diagram/101044/2
This is an intro. There is much more to be said about it - do some reading to find out what it represents. It is a graph of one thing vs. another, on which stars are plotted. Most reside in a certain area of the graph - the location of a star on the graph gives us information about the type of star and where it is in its life.
Read, make notes, come to class Wednesday prepared to discuss.
For later:
http://en.wikipedia.org/wiki/List_of_nearest_stars
http://en.wikipedia.org/wiki/List_of_brightest_stars
Monday, December 10, 2012
Thursday, December 6, 2012
Dates of note
Lab due next Friday (12/14)
Quiz on the sky, etc. (12/18)
Night class (12/18)
Winter solstice (12/21, but we can have a class party on the 20th - bring food, if you like!)
Quiz on the sky, etc. (12/18)
Night class (12/18)
Winter solstice (12/21, but we can have a class party on the 20th - bring food, if you like!)
Observing lab - due 12/14/12
Observing lab
Grab some hot chocolate and enjoy the late fall / early winter sky!
1. List asterisms that you can find.
2. List constellations you can find.
3. What are the brightest objects in the sky tonight (other than the Moon, if it is visible)?
4. What phase is the Moon? You may need to consult a chart, if it is not visible.
5. What stars make up the "winter triangle"? Is it visible?
6. What stars make up the "winter hexagon"? Is it visible?
7. What planets are visible?
8. Find Orion. Draw it as you see it.
9. Answer these questions based on Orion:
a. What are the 2 brightest stars. Give names and colors.
b. List the names of the belt stars.
c. Following the belt stars (in either direction), find the next bright star(s) and identify them (and their constellations).
10. What is directly overhead (at zenith), more or less?
11. Roughly, where is the Andromeda galaxy (M31)? Can you see it?
12. Locate the Pleiades cluster, using Orion as a guide. Describe your technique and draw it, if possible.
13. Locate Castor and Pollux (in Gemini) using Orion as a guide. Describe your technique.
14. Find north and face that direction. Now locate Cassiopeia (by coming due south) and draw it as you see it.
15. Can you still see the summer triangle?
16. Using Cassiopeia as a guide, locate the great square of Pegasus and the Northern Cross (in Cygnus). Describe your technique.
17. List anything else interesting you were able to find.
18. Comment on general viewing conditions in your area.
Grab some hot chocolate and enjoy the late fall / early winter sky!
1. List asterisms that you can find.
2. List constellations you can find.
3. What are the brightest objects in the sky tonight (other than the Moon, if it is visible)?
4. What phase is the Moon? You may need to consult a chart, if it is not visible.
5. What stars make up the "winter triangle"? Is it visible?
6. What stars make up the "winter hexagon"? Is it visible?
7. What planets are visible?
8. Find Orion. Draw it as you see it.
9. Answer these questions based on Orion:
a. What are the 2 brightest stars. Give names and colors.
b. List the names of the belt stars.
c. Following the belt stars (in either direction), find the next bright star(s) and identify them (and their constellations).
10. What is directly overhead (at zenith), more or less?
11. Roughly, where is the Andromeda galaxy (M31)? Can you see it?
12. Locate the Pleiades cluster, using Orion as a guide. Describe your technique and draw it, if possible.
13. Locate Castor and Pollux (in Gemini) using Orion as a guide. Describe your technique.
14. Find north and face that direction. Now locate Cassiopeia (by coming due south) and draw it as you see it.
15. Can you still see the summer triangle?
16. Using Cassiopeia as a guide, locate the great square of Pegasus and the Northern Cross (in Cygnus). Describe your technique.
17. List anything else interesting you were able to find.
18. Comment on general viewing conditions in your area.
Stuff from today's class
http://vimeo.com/22582065
The Pale Blue Dot video (narrated by Carl Sagan)
http://www.youtube.com/watch?v=YXh9RQCvxmg
Neil deGrasse Tyson with Colbert
http://www.youtube.com/watch?v=Bgaw9qe7DEE
And if you ever have an hour to spare, Richard Feynman (a hero of mine):
http://www.randi.org/site/index.php/swift-blog/1942-taking-the-lift-out-of-street-levitation-with-physics.html
For fun
http://www.youtube.com/watch?feature=player_embedded&v=LR-MSZSLC5w
Just because....
The Wien Displacement law:
The Pale Blue Dot video (narrated by Carl Sagan)
http://www.youtube.com/watch?v=YXh9RQCvxmg
Neil deGrasse Tyson with Colbert
http://www.youtube.com/watch?v=Bgaw9qe7DEE
And if you ever have an hour to spare, Richard Feynman (a hero of mine):
http://www.randi.org/site/index.php/swift-blog/1942-taking-the-lift-out-of-street-levitation-with-physics.html
For fun
http://www.youtube.com/watch?feature=player_embedded&v=LR-MSZSLC5w
Just because....
The Wien Displacement law:
where λmax is the peak wavelength, T is the absolute temperature of the black body, and b is a constant of proportionality called Wien's displacement constant, equal to 2.8977685(51)×10−3 m·K (2002 CODATA recommended value).
Doppler Effect
Dopper Effect
See this simple, but effective applet:
http://lectureonline.cl.msu.edu/~mmp/applist/doppler/d.htm
In this simulation, v/vs is the ratio of your speed to the speed of sound; e.g., 0.5 is you, or the blue dot, traveling at half the speed of sound. Note how the waves experienced on one side "pile up" (giving an observer a greater detected frequency, or BLUE SHIFT); on the other side, the waves are "stretched apart" (giving an observer a lower detected frequency, or RED SHIFT).
Play with this for a bit, though it's a little less obvious:
http://falstad.com/ripple/
In astronomy, the red shift is very important historically: Edwin Hubble found that light from distant galaxies (as measured in their spectra) was red shifted, meaning that distant galaxies were moving away from us (everywhere we looked). The conclusion was obvious (and startling): The universe is expanding. Last year, local astrophysicist Adam Riess discovered that the rate of expansion was accelerating.
http://www.nobelprize.org/nobel_prizes/physics/laureates/2011/
It's worth noting that the effect also works in reverse. If you (the detector) move toward a sound-emitter, you'll detect a higher frequency. If you move away from a detector move away from a sound-emitter, you'll detect a lower frequency.
Mind you, these Doppler effects only happen WHILE there is relative motion between source and detector (you).
And of course, they also work for light. That's why we care about them. In fact, the terms red shift and blue shift refer mainly to light (or other electromagnetic) phenomena.
H-R diagram lab
Lab 6 - The Hertzsprung-Russell Diagram
One of the most useful tools for identifying star types in astronomy is the H-R Diagram. This idea, independently conceived in 1910 by Ejnar Hertzsprung and Henry Russell, is a graphical representation of intrinsic brightness as a function of temperature. It is largely based on this diagram that stars are classified.
There are a few variations of the H-R diagram:
• Absolute visual magnitude (Mv) vs. Spectral Type
• Absolute visual magnitude vs. Temperature
• Luminosity of star (sometimes given as relative to Sun’s luminosity) vs. Spectral Type
• Absolute visual magnitude vs. Color Index (B - V)
Other variations exist as well. The purpose and effect of each diagram is the same, however. Points plotted fall in limited regions on the graph, rather than in a wide distribution.
In today’s lab, you will plot an H-R diagram for the nearest and brightest stars, as given in the text appendices. Plot the Absolute visual magnitude (or Mv) versus the Spectral Type. Recall the Spectral Types are (in order of decreasing temperature):
O, B, A, F, G, K, M
Further, each of these can be subdivided into 10 categories, 0-9, though most of our stars today will be in the 0-5 range. Your graph will resemble the graph noted on the board in class.
Lab
Set up an H-R diagram for all of the brightest stars. y-axis (Absolute Visual Magnitude) should run from at least +16 to -7 (bottom to top), while the x-axis (Spectral Type) should include all classifications (and subdivisions) listed above. You may opt to include only those stars which are in subdivisions 0-5; this will eliminate a few stars.
Shade in the rough area which represents the Main Sequence of stars. Recall that this is a broad roughly diagonal band running from upper left to lower right.
Questions
1. How is temperature of a star determined?
2. What type of star is the sun?
3. What is another name for a dwarf star?
4. From the H-R diagram, identify stars which are giants.
5. Which of these are more likely to be supergiants?
6. Identify likely candidates for white dwarf stars.
One of the most useful tools for identifying star types in astronomy is the H-R Diagram. This idea, independently conceived in 1910 by Ejnar Hertzsprung and Henry Russell, is a graphical representation of intrinsic brightness as a function of temperature. It is largely based on this diagram that stars are classified.
There are a few variations of the H-R diagram:
• Absolute visual magnitude (Mv) vs. Spectral Type
• Absolute visual magnitude vs. Temperature
• Luminosity of star (sometimes given as relative to Sun’s luminosity) vs. Spectral Type
• Absolute visual magnitude vs. Color Index (B - V)
Other variations exist as well. The purpose and effect of each diagram is the same, however. Points plotted fall in limited regions on the graph, rather than in a wide distribution.
In today’s lab, you will plot an H-R diagram for the nearest and brightest stars, as given in the text appendices. Plot the Absolute visual magnitude (or Mv) versus the Spectral Type. Recall the Spectral Types are (in order of decreasing temperature):
O, B, A, F, G, K, M
Further, each of these can be subdivided into 10 categories, 0-9, though most of our stars today will be in the 0-5 range. Your graph will resemble the graph noted on the board in class.
Lab
Set up an H-R diagram for all of the brightest stars. y-axis (Absolute Visual Magnitude) should run from at least +16 to -7 (bottom to top), while the x-axis (Spectral Type) should include all classifications (and subdivisions) listed above. You may opt to include only those stars which are in subdivisions 0-5; this will eliminate a few stars.
Shade in the rough area which represents the Main Sequence of stars. Recall that this is a broad roughly diagonal band running from upper left to lower right.
Questions
1. How is temperature of a star determined?
2. What type of star is the sun?
3. What is another name for a dwarf star?
4. From the H-R diagram, identify stars which are giants.
5. Which of these are more likely to be supergiants?
6. Identify likely candidates for white dwarf stars.
Tuesday, December 4, 2012
HW for Thursday
Play around a bit with this blackbody radiation applet:
http://lectureonline.cl.msu.edu/~mmp/applist/blackbody/black.htm
By changing the absolute temperature (in K), you change the output of the star.
More here:
http://cas.sdss.org/dr6/en/proj/advanced/color/physlet/blackbody.asp
If you are able, have a look into the equation for blackbody radiation. It's complicated, and is sometimes called Planck's law. You may be interested in how similar (or not) it is to a Gaussian (normal) distribution (bell curve).
Also, review the idea of the Doppler effect. Try to find an equation for it (specifically one that has wavelengths in it). It shouldn't be too complex an expression, but it should be suitable for light (rather than sound).
Finally, review the ideas of the electromagnetic spectrum. Here's an image below. Recall that the product of frequency (f) and wavelength (lambda) are always constant: the speed of light. Or if you prefer: c = f l
http://lectureonline.cl.msu.edu/~mmp/applist/blackbody/black.htm
By changing the absolute temperature (in K), you change the output of the star.
More here:
http://cas.sdss.org/dr6/en/proj/advanced/color/physlet/blackbody.asp
If you are able, have a look into the equation for blackbody radiation. It's complicated, and is sometimes called Planck's law. You may be interested in how similar (or not) it is to a Gaussian (normal) distribution (bell curve).
Also, review the idea of the Doppler effect. Try to find an equation for it (specifically one that has wavelengths in it). It shouldn't be too complex an expression, but it should be suitable for light (rather than sound).
Finally, review the ideas of the electromagnetic spectrum. Here's an image below. Recall that the product of frequency (f) and wavelength (lambda) are always constant: the speed of light. Or if you prefer: c = f l
Subscribe to:
Posts (Atom)