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Home , Orion Arm, Perseus Arm

Reminder and Announcement

• Classroom changed! Watanabe 415 • Mastering HW0 due this Friday • Mastering Astronomy HW1 is available today, due next Tuesday • Come talk to Nick or Chao-Ling after class if you have any question about Mastering Astronomy What we learned yesterday

• Idea about Science and Astronomy • a bit useful math for Astronomy • relative size and distance of , and the What are we going to learn today

• Build some idea about scales of Astronomical objects • How do we describe the size/distance scale of these objects

OUR PLACE IN THE ?

What is our Cosmic Address? Our place in the Universe?

Class Action! Your friends, Roy and Mike, rulers of Omicron Persei 8, want to send you a postcard via the Cosmic Postal Service. The CPS is very strict about complete addresses on all mail! Help them by using all seven of the terms in the box to complete your cosmic address — put them in order, from smallest to largest: Our place in the Universe?

Do this yourselves (no discussion) Write down your answers on the worksheet complete your cosmic address — put them in order, from smallest to largest:

Dear Friend, Earth We hear that you are taking astronomy this semester, eh? Just The TO: keep your telescopes pointed away The your name: ______from !! Heh, just kidding. your street: ______We just got back from a quick trip The Arm your city: ______up the to the Bulge — your state: ______The we saw some gorgeous nebulae along your country: ______the way. The Universe ______Things here on omicron Per 8 are the ______The same as usual - 200˚C and lots of ______hydrocarbon haze. At least we’re ______getting stellar panels installed next ______month to help lower our energy bill! ______Write back soon, ______Lrrr & Ndnd OUR PLACE IN THE UNIVERSE?

What is our Cosmic Address? Our place in the Universe?

Answer

Orion arm Our place in the Universe?

Answer Our place in the Universe?

Honolulu

Hawaii

2680 Woodlawn Drive Honolulu, Hawaii, USA 96822-1839

USA Our place in the Universe?

20 miles 1 Honolulu

300 miles Hawaii 15 2680 Woodlawn Drive Honolulu, Hawaii, USA 96822-1839

2500 miles USA 125 • Describe our “cosmic address” Earth

Radius = 6370 km Earth-Sun

Earth - Sun average distance = 145,980,000 km = 1.4598 x 108 km = 20000 Earth radii = 1 Astronomical Unit (AU)

At the scale of the Solar System distances are described in terms of the Astronomical Unit or AU. Solar System

• Earth is the third from the sun • The solar system consists of the Sun and other astronomical objects. Light Travel Time

Light travels at 3 x 105 km/sec through the vacuum of space. We can use how long does it take for light to travel from point A to B as a measure of the distance from point A to B.

Milky Way Galaxy

• The Milky Way is the galaxy in which the solar system is contained. • It is a • Contains 300 billion stars. Milky Way Galaxy

Disk radius = 3.162 x 109 AU Orion arm = 50,000 ly Disk thickness = 1,000 ly Local Group

• The Local Group is the group of galaxies that includes Milky Way. • It has ~50 galaxies • It has a binary distribution Local Group

Distance to Andromeda (M31) = 2.5 x 106 ly

Virgo Supercluster

• The Virgo Supercluster is a irregular supercluster that includes the Local Group • It has ~100 galaxy group and clusters Virgo Supercluster

Diameter = 2 x 108 ly

The Universe

• The Universe is commonly defined as the totality of everything that exists. The Universe

9.3 x 1010 ly across 13.3 billion years old

Lecture Tutorial

• Break up into groups of 2-3 –NO MORE THAN 3 • In your group, work through the following: -Looking at Distant Objects (pages 131-132): Question 1 to 8 –Discuss the answers – don’t be silent! • I will be roaming around if you need help… • If your group finishes, check your answers with another group