astronomy 210 a survey of astronomy office hours: paul coleman: mwf (10:30-11:30;12:30-13:30)...
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ASTRONOMY 210 a survey of astronomy
Office Hours: Paul Coleman: MWF (10:30-11:30;12:30-13:30)
Watanabe 401 pcoleman@ifa.hawaii.edu
Grad St.Course details and notes:
http://www.ifa.hawaii.edu/users/gruff/default/Coleman.htmlhttp://www.ifa.hawaii.edu/users/gruff/default/astro210.html
Phasers on Stun!!
Cell phones on vibrate please!
Weekly quizzes….• If you will miss it contact me in
advance… Makeups will be held on the Monday following
• One question on the weekly homework problem
• One question on the material in the readings
Spaceship Earth
• Describe the basic motions of “spaceship Earth.”• How do we know that the Universe is
expanding?
Movers…
• “We never get to go anywhere”• “It costs too much to go anywhere”
and Shakers…
• Nothing could be further from the truth…
During the half-minute we’ve been looking at this slide, we have traveled ~400 miles.
We are whizzing through space in at least four different directions!
Why don’t we feel the motion?
Motion I
Face the rising sun in the morning. That's our first direction of celestial movement.
r
Circumference = 2pr
Motion ICircumference = 2pr ~ 25000
milesTime = 24 hours
1042 mph !!!!hours
milesv timedistance
2425000
1
r = 1 AU = 1.5 x 1011 meters
Motion II
Motion IIWe are zooming around the sun at
64,800 mph!!!
N
West
r
Motion III
Our Sun is but one of some 100 billion stars that makes up our home galaxy, the Milky Way. It takes our sun about 226 million years to circle the Milky Way.
With the measured distance to the Galactic Center we calculate a speed of about 486,000 mph.
Look a little above the horizon about 20 degrees west of directly south – you are traveling in that direction! The center of the Galaxy is located between the two constellations Scorpius and Sagittarius. 90 degrees away from this direction (toward Dorado) is the direction we are going as we orbit the galaxy at 135 miles per second.
Motion III
Motion IV Look South around midnight in june,
you'll see the beautiful Southern Cross low on the horizon. Right above it is the constellation Centaurus.
That's the direction our solar system and galaxy is headed at more than a million miles per hour!
Take your pick:
1. Earth’s rotational speed = 1042 mph2. Earth’s orbital speed = 64,800 mph 3. Sun’s orbital speed = 486,000 mph4. Milky Way’s speed = 1,000,000 mph (Not to mention the expansion of the universe!)
In the ~20 minutes so far for this talk, we have moved about 350 miles east and about 21,600 miles around the sun. Our solar system has moved 162,000 miles around the galaxy and we've moved about 340,000 miles closer to Hercules.
For a grand total of about 420,000 miles traveled!
Too bad we don't get frequent flyer miles for this.
How large is the Solar System?• Let’s view it to scale
– say the Sun is the size of a CD (~12 cm)– then:
Earth – 15 mMars – 23 mJupiter – 78 mSaturn –143 mUranus – 287 m
The Celestial Sphere• The sky above looks like a
dome…a hemisphere..• If we imagine the sky
around the entire Earth, we have the celestial sphere.
• This a 2-dimensional representation of the sky
Because it represents our view from Earth, we place the Earth in the center of this sphere.
The Celestial Sphere
North & South celestial polesthe points in the sky directly above the Earth’s North and South poles
celestial equatorthe extension of the Earth’s equator onto the celestial sphere
eclipticthe annual path of the Sun through the celestial sphere, which is a projection of ecliptic plane
© 2004 Pearson Education Inc., publishing as Addison-Wesley
A spinning imaginary Celestial Sphere
surrounding Earth aids in navigating
the sky
Measuring the Sky
We measure the sky in angles, not distances.
• Full circle = 360º• 1º = 60 arcmin • 1 arcmin = 60 arcsec
Angular Measurements and Notation:
• Full circle = 360º• 1º = 60 (arcminutes) • 1 = 60 (arcseconds)
Homework #1• 45.635 degrees is how many degrees, arcminutes, and arcseconds?
• How many degrees, arcminutes, and arcseconds does the moon move across the sky in one hour? (the lunar day is 24 hours and 48 minutes long)
• The moons diameter is about 30 arcminutes, so find out how long it takes for the moon to travel its diameter.
Measuring Angles in the Sky
The Local Skyzenith
the point directly above you
horizonall points 90° from the zenith
altitudethe angle above the horizon
meridiandue north horizon zenith due south horizon
To pinpoint a spot in the local sky:
Specify altitude and direction along the horizon
Elements of the equatorial coordinate system on the celestial sphere
• Vernal Equinox: The position of the Sun on the first day of spring (Sets the prime meridian)
• Right Ascension: How far east of the Vernal Equinox an object is located – measured as time! (longitude)
• Celestial Equator: The line separating the celestial sphere into northern and southern halves.
• Declination: How far above or below the celestial equator an object is located.(latitude)
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