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)