The forecast is pretty much 100% guaranteed rain, clouds, fog after midnight.
So, we'll have to try this again a different morning. Sorry!
Monday, November 26, 2012
Wednesday, November 21, 2012
Thanks!
Great night for viewing! Thanks to those who could make it - much appreciated!
Have no fear, Astro friends. We'll view again soon. Until then, this cool graphic:
Have no fear, Astro friends. We'll view again soon. Until then, this cool graphic:
Clear so far!
I plan to be at school tonight. Text me if you're not sure whether or not it is still clear. Hope to see you (and anyone you wish to bring) tonight!
TONIGHT - WEDNESDAY
We'll be here at 8 PM, if the weather holds.
Watch the blog for an update by 6 PM.
Watch the blog for an update by 6 PM.
Tuesday, November 20, 2012
CLOUDY
No viewing tonight.
Try again tomorrow (Wednesday) night. I'll call it again by 6 PM tomorrow night. Sorry, friends. And today is Edwin Hubble's birthday!
Try again tomorrow (Wednesday) night. I'll call it again by 6 PM tomorrow night. Sorry, friends. And today is Edwin Hubble's birthday!
Monday, November 19, 2012
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 R^2 s T^4
R is the radius of the body emitting light, s is the Stefan-Boltzmann
constant (5.67 x 10-8 W/m^2K^4) 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 R^2 s T^4
R is the radius of the body emitting light, s is the Stefan-Boltzmann
constant (5.67 x 10-8 W/m^2K^4) 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)
Friday, November 16, 2012
Interesting?
http://www.wired.com/geekdad/2012/11/exclusive-bt-video/
Watch - what do you think?
Also, turn in either the Planets lab or the Sundial on Tuesday.
Watch - what do you think?
Also, turn in either the Planets lab or the Sundial on Tuesday.
Wednesday, November 14, 2012
Stuff.
Tentative star-gazing night is next Tuesday, Nov 20, 8 PM.
Also - check this out:
http://www.msnbc.msn.com/id/49823152/ns/technology_and_science-space/
Also - check this out:
http://www.msnbc.msn.com/id/49823152/ns/technology_and_science-space/
Tuesday, November 13, 2012
Planet "lab"
Lab 4 - Tour of the Planets
Please determine many interesting tidbits of trivia about our solar neighbors. You may like the following website:
http://nineplanets.org/
Please answer the following questions, based on your reading and web discovery. Some questions might have several answers, while the answer to others might be "none of them."
Please determine many interesting tidbits of trivia about our solar neighbors. You may like the following website:
http://nineplanets.org/
Please answer the following questions, based on your reading and web discovery. Some questions might have several answers, while the answer to others might be "none of them."
Which planet(s):
1. Rotates backwards?
2. Revolves backwards?
3. Rotates nearly on its side?
4. Have more than 10 moons?
5. Have only one moon?
6. Has an orbit with the greatest inclination to the ecliptic?
7. Is the furthest planet known to the ancients?
8. Has a largely methane atmosphere?
9. Has a nondescript, pale greenish color?
10. Has a blemish known as the great dark spot?
11. Has a fine iron oxide regolith?
12. Is most similar to Earth in its surface gravity?
13. Has the greatest mass?
14. Has the smallest diameter?
15. Have been visited by humans?
16. Has the strongest magnetic field?
17. Has rings?
18. Has sulfuric acid clouds?
19. Has the tallest mountain in the Solar System (and what is it)?
20. Has a day longer than its year?
21. Has been landed on most recently by spacecraft?
22. Experiences global dust storms?
23. Has a moon that rotates retrograde (and what is it)?
24. May be an escaped Kuiper object?
25. Was once thought to be a failed star?
26. Is heavily cratered?
27. Has moons which are likely candidates for life?
28. Was hit by a large comet in the last several years?
29. Is most oblate?
30. Has a central pressure 100 million times Earth's atmospheric pressure?
Now for the minor bodies.
1. Which body is an asteroid with its own orbiting asteroid?
2. Which moon has erupting volcanoes?
3. Which body is the largest asteroid?
4. Approximately how many known asteroids are there?
5. Approximately how many known Kuiper objects are there? What is the Kuiper belt?
6. How large is the Oort Cloud? What is the Oort Cloud?
7. Which moon was the first discovered after the Galilean satellites?
1. Rotates backwards?
2. Revolves backwards?
3. Rotates nearly on its side?
4. Have more than 10 moons?
5. Have only one moon?
6. Has an orbit with the greatest inclination to the ecliptic?
7. Is the furthest planet known to the ancients?
8. Has a largely methane atmosphere?
9. Has a nondescript, pale greenish color?
10. Has a blemish known as the great dark spot?
11. Has a fine iron oxide regolith?
12. Is most similar to Earth in its surface gravity?
13. Has the greatest mass?
14. Has the smallest diameter?
15. Have been visited by humans?
16. Has the strongest magnetic field?
17. Has rings?
18. Has sulfuric acid clouds?
19. Has the tallest mountain in the Solar System (and what is it)?
20. Has a day longer than its year?
21. Has been landed on most recently by spacecraft?
22. Experiences global dust storms?
23. Has a moon that rotates retrograde (and what is it)?
24. May be an escaped Kuiper object?
25. Was once thought to be a failed star?
26. Is heavily cratered?
27. Has moons which are likely candidates for life?
28. Was hit by a large comet in the last several years?
29. Is most oblate?
30. Has a central pressure 100 million times Earth's atmospheric pressure?
Now for the minor bodies.
1. Which body is an asteroid with its own orbiting asteroid?
2. Which moon has erupting volcanoes?
3. Which body is the largest asteroid?
4. Approximately how many known asteroids are there?
5. Approximately how many known Kuiper objects are there? What is the Kuiper belt?
6. How large is the Oort Cloud? What is the Oort Cloud?
7. Which moon was the first discovered after the Galilean satellites?
8. How many "extrasolar" planets are there? Which was the first discovered?
9. What is the status of Pluto and why was is "demoted" from planet status?
Additional - list something you found interesting in your hunt. Or multiple things.
Friday, November 9, 2012
Moon Phases, etc.
http://astro.unl.edu/naap/lps/animations/lps.html
http://www.astro.wisc.edu/~dolan/java/MoonPhase.html
http://www.moonconnection.com/moon_phases.phtml
http://www.astro.wisc.edu/~dolan/java/MoonPhase.html
http://www.moonconnection.com/moon_phases.phtml
Thursday, November 1, 2012
extra credit
Folks - there were inquiries about extra credit. That's ok. If you're interested, chat with me quickly. Here are ideas:
Write about one of these ideas:
Lagrange points
Equation of time
Analemma
Write about one of these ideas:
Lagrange points
Equation of time
Analemma
Subscribe to:
Posts (Atom)