http://www.thedailyshow.com/watch/wed-april-25-2012/space-innovators?xrs=synd_twtbtn&xrs=eml_tds
Get through as much of the wikipedia entry on sundials as you can.
http://en.wikipedia.org/wiki/Sundial
Friday, April 27, 2012
Sunday, April 22, 2012
meteor shower fyi
The weather is not cooperating, but if it clears tonight, have a peek outside for the Lyrids:
http://news.blogs.cnn.com/2012/04/21/your-guide-to-the-lyrid-meteor-shower/?hpt=hp_t2
http://news.blogs.cnn.com/2012/04/21/your-guide-to-the-lyrid-meteor-shower/?hpt=hp_t2
Friday, April 20, 2012
sundials!
Gang,
For Monday's class, do a little preliminary research on Sundials. You (either alone or with a partner) will be building one. They can be horizontal, vertical, equatorial, etc., but they must be functional.
See you Monday!
sean
For Monday's class, do a little preliminary research on Sundials. You (either alone or with a partner) will be building one. They can be horizontal, vertical, equatorial, etc., but they must be functional.
See you Monday!
sean
Tuesday, April 17, 2012
Sunday, April 15, 2012
Wednesday, April 11, 2012
Dopper Effect HW etc.
Apologies for getting this out there late. Do it if you have time.
Read up a bit on the Doppler Effect - it may be review for you from physics. Or not.
Also, look into the Hertzsprung-Russell diagram.
Related to the Doppler 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.
Read up a bit on the Doppler Effect - it may be review for you from physics. Or not.
Also, look into the Hertzsprung-Russell diagram.
Related to the Doppler 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.
Tuesday, April 10, 2012
Reminder about tonight
8 PM tonight (Tuesday, April 10) at the observatory/roof.
If it's cloudy, we'll aim for tomorrow night.
If in doubt, call/text: 412-965-0805
If it's cloudy, we'll aim for tomorrow night.
If in doubt, call/text: 412-965-0805
Monday, April 9, 2012
New 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.
The Doppler Effect
http://falstad.com/ripple/
See also 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).
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 they also work for light. In fact, the terms red shift and blue shift refer mainly to light (or other electromagnetic) phenomena.
Monday, April 2, 2012
Angular Measurement and Magnitude
Angular Measurement
Consider the following convention which has been with us since the rise of Babylonian mathematics:
There are 360 degrees per circle.
Each degree can be further divided into 60 minutes (60’), each called an arcminute.
Each arcminute can be divided into 60 seconds (60”), each called an arcsecond.
Therefore, there are 3600 arcseconds in one degree.
Some rough approximations:
A fist extended at arm’s length subtends an angle of approx. 10º.
A thumb extended at arm’s length subtends an angle of approx. 2º.
The Moon (and Sun) subtend an angle of approx. 0.5º.
Human eye resolution (the ability to distinguish between 2 adjacent objects) is limited to about 1 arcminute – roughly the diameter of a dime at 60-m. Actually, given the size of our retina, we’re limited to a resolution of roughly 3’.
So, to achieve better resolution, we need more aperture (ie., telescopes).
The Earth’s atmosphere limits detail resolution to objects bigger than 0.5”, the diameter of a dime at 7-km, or a human hair 2 football fields away. This is usually reduced to 1” due to atmospheric turbulence.
The parsec (pc)
The distance at which 1 AU subtends an angle of one arcsec (1”) is definite as one parsec – that is, it has a parallax of one arcsec.
For example, if a star has a parallax angle (d) of 0.5 arcsec, it is 1/0.5 parsecs (or 2 parsecs) away.
The parsec (pc) is roughly 3.26 light years.
Distance (in pc) = 1 / d
where d is in seconds of arc.
Measuring star distances can be done by measuring their angle of parallax – typically done over a 6-month period, seeing how the star’s position changes with respect to background stars in 6 months, during which time the Earth has moved across its ellipse.
Unfortunately, this is limited to nearby stars, some 10,000. Consider this: Proxima Centauri (nearest star) has a parallax angle of 0.75” – a dime at 5-km. So, you need to repeat measurements over several years for accuracy.
This works for stars up to about 300 LY away, less than 1% the diameter of our galaxy!
[If the MW galaxy were reduced to 130 km (80 mi) in diameter, the Solar System would be a mere 2 mm (0.08 inches) in width.]
Apparent magnitude (m) scale
This dates back to the time of Hipparchus who classified things as bright or small.
Ptolemy classified things into numbers: 1-6, with 1 being brightest. The brightest (1st magnitude) stars were 100 times brighter than the faintest (6th magnitude). This convention remains standard to this day. Still, this was very qualitative.
In the 19th century, with the advent of photographic means of recording stars onto plates, a more sophisticated system was adopted. It held to the original ideas of Ptolemy
A difference of 5 magnitudes (ie., from 1 to 6) is equivalent to a factor of exactly 100 times. IN other words, 1st magnitude is 100x brighter than 6th magnitude. Or, 6th magnitude is 1/100th as bright as 1st mag.
This works well, except several bodies are brighter than (the traditional) 1st mag.
So….. we have 0th magnitude and negative magnitudes for really bright objects.
Examples:
Sirius (brightest star): -1.5
Sun: -26.8
Moon: -12.6
Venus: -4.4
Canopus (2nd brightest star): -0.7
Faintest stars visible with eye: +6
Faintest stars visible from Earth: +24
Faintest stars visible from Hubble: +28
The magnitude factor is the 5th root of 100, which equals roughly 2.512 (about 2.5).
Keep in mind that this is APPARENT magnitude, which depends on distance, actual star luminosity and interstellar matter.
Here’s a problem: What is the brightness difference between two objects of magnitudes -1 and 6?
Since they are 7 magnitudes apart, the distance is 2.5 to the 7th power, or 600.
For the math buffs: the formula for apparent magnitude comparison:
m1 – m2 = 2.5 log (I2 / I1)
The m’s are magnitudes and the I’s are intensities – the ratio of the intensities gives a comparison factor. A reference point is m = 100, corresponding to an intensity of 2.65 x 10-6 lumens.
FYI: Absolute Magnitude, M
Consider how bright the star would be if it were 10 pc away. This is how we define absolute magnitude (M).
It depends on the star’s luminosity, which is a measure of its brightness:
L = 4 p R2 s T4
R is the radius of the body emitting light, s is the Stefan-Boltzmann constant (5.67 x 10-8 W/m2K4) and T is the effective temperature (in K) of the body.
If the star is 10 pm away, its M = m (by definition).
m – M = 5 log (d/10)
We let d = the distance (in pc), log is base 10, m is apparent magnitude and M is absolute magnitude.
A problem: If d = 20 pc and m = +4, what is M? (2.5)
And another (more challenging):
If M = 5 and m = 10, how far away is the star? (100 pc)
Consider the following convention which has been with us since the rise of Babylonian mathematics:
There are 360 degrees per circle.
Each degree can be further divided into 60 minutes (60’), each called an arcminute.
Each arcminute can be divided into 60 seconds (60”), each called an arcsecond.
Therefore, there are 3600 arcseconds in one degree.
Some rough approximations:
A fist extended at arm’s length subtends an angle of approx. 10º.
A thumb extended at arm’s length subtends an angle of approx. 2º.
The Moon (and Sun) subtend an angle of approx. 0.5º.
Human eye resolution (the ability to distinguish between 2 adjacent objects) is limited to about 1 arcminute – roughly the diameter of a dime at 60-m. Actually, given the size of our retina, we’re limited to a resolution of roughly 3’.
So, to achieve better resolution, we need more aperture (ie., telescopes).
The Earth’s atmosphere limits detail resolution to objects bigger than 0.5”, the diameter of a dime at 7-km, or a human hair 2 football fields away. This is usually reduced to 1” due to atmospheric turbulence.
The parsec (pc)
The distance at which 1 AU subtends an angle of one arcsec (1”) is definite as one parsec – that is, it has a parallax of one arcsec.
For example, if a star has a parallax angle (d) of 0.5 arcsec, it is 1/0.5 parsecs (or 2 parsecs) away.
The parsec (pc) is roughly 3.26 light years.
Distance (in pc) = 1 / d
where d is in seconds of arc.
Measuring star distances can be done by measuring their angle of parallax – typically done over a 6-month period, seeing how the star’s position changes with respect to background stars in 6 months, during which time the Earth has moved across its ellipse.
Unfortunately, this is limited to nearby stars, some 10,000. Consider this: Proxima Centauri (nearest star) has a parallax angle of 0.75” – a dime at 5-km. So, you need to repeat measurements over several years for accuracy.
This works for stars up to about 300 LY away, less than 1% the diameter of our galaxy!
[If the MW galaxy were reduced to 130 km (80 mi) in diameter, the Solar System would be a mere 2 mm (0.08 inches) in width.]
Apparent magnitude (m) scale
This dates back to the time of Hipparchus who classified things as bright or small.
Ptolemy classified things into numbers: 1-6, with 1 being brightest. The brightest (1st magnitude) stars were 100 times brighter than the faintest (6th magnitude). This convention remains standard to this day. Still, this was very qualitative.
In the 19th century, with the advent of photographic means of recording stars onto plates, a more sophisticated system was adopted. It held to the original ideas of Ptolemy
A difference of 5 magnitudes (ie., from 1 to 6) is equivalent to a factor of exactly 100 times. IN other words, 1st magnitude is 100x brighter than 6th magnitude. Or, 6th magnitude is 1/100th as bright as 1st mag.
This works well, except several bodies are brighter than (the traditional) 1st mag.
So….. we have 0th magnitude and negative magnitudes for really bright objects.
Examples:
Sirius (brightest star): -1.5
Sun: -26.8
Moon: -12.6
Venus: -4.4
Canopus (2nd brightest star): -0.7
Faintest stars visible with eye: +6
Faintest stars visible from Earth: +24
Faintest stars visible from Hubble: +28
The magnitude factor is the 5th root of 100, which equals roughly 2.512 (about 2.5).
Keep in mind that this is APPARENT magnitude, which depends on distance, actual star luminosity and interstellar matter.
Here’s a problem: What is the brightness difference between two objects of magnitudes -1 and 6?
Since they are 7 magnitudes apart, the distance is 2.5 to the 7th power, or 600.
For the math buffs: the formula for apparent magnitude comparison:
m1 – m2 = 2.5 log (I2 / I1)
The m’s are magnitudes and the I’s are intensities – the ratio of the intensities gives a comparison factor. A reference point is m = 100, corresponding to an intensity of 2.65 x 10-6 lumens.
FYI: Absolute Magnitude, M
Consider how bright the star would be if it were 10 pc away. This is how we define absolute magnitude (M).
It depends on the star’s luminosity, which is a measure of its brightness:
L = 4 p R2 s T4
R is the radius of the body emitting light, s is the Stefan-Boltzmann constant (5.67 x 10-8 W/m2K4) and T is the effective temperature (in K) of the body.
If the star is 10 pm away, its M = m (by definition).
m – M = 5 log (d/10)
We let d = the distance (in pc), log is base 10, m is apparent magnitude and M is absolute magnitude.
A problem: If d = 20 pc and m = +4, what is M? (2.5)
And another (more challenging):
If M = 5 and m = 10, how far away is the star? (100 pc)
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