ASTRONOMY 210 a survey of astronomy Office Hours: Paul Coleman: MWF (10:30-11:30;12:30-13:30) Watanabe 401 Grad St. Course details and notes:

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… Movers… “We never get to go anywhere” “We never get to go anywhere” “It costs too much 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 = 2  r

Motion I Circumference = 2  r ~ miles Time = 24 hours 1042 mph !!!!

r = 1 AU = 1.5 x meters Motion II

We are zooming around the sun at 64,800 mph!!! 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. 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! 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 mph 2.Earth’s orbital speed = 64,800 mph 3.Sun’s orbital speed = 486,000 mph 4.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 m Mars – 23 m Jupiter – 78 m Saturn –143 m Uranus – 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 poles the points in the sky directly above the Earth’s North and South poles celestial equator the extension of the Earth’s equator onto the celestial sphere ecliptic the 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 # 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 Sky zenith the point directly above you horizon all points 90° from the zenith altitude the angle above the horizon meridian due 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)