Welcome to

Astronomy!

Introduction tothe

Universe

Astro 1105/1107Prof. Julia Kregenow

A large, glowing ball of gas that generates heat and light through nuclear fusion

Star

GalaxyA great island of stars in space, all held

together by gravity and orbiting a common center

M31, The Great Galaxy in Andromeda

Universe

The sum total of all matter and energy; that is, everything within and between

all galaxies

Your Goals: Brief Survey

What do you want to learn about astronomy?

Write down a few things.

My Goals: on Syllabus

On course website: www.astro.cornell.edu/academics/courses/astro105/

Please read it carefully!

Homework for TOMORROW

• Read Syllabus online -- quiz tomorrow!– The syllabus is our CONTRACT

• Register on “MasteringAstronomy” website – Instructions on our course webpage www.astro.cornell.edu/academics/courses/astro105/

– Enroll in our course: (ID# given on syllabus)

• First online assignment due tomorrow 10:30am– “Introduction to MasteringAstronomy” (see HW page)

SOME REALLY BIG IDEAS

ScienceLight

Lookback timeGravity

Star stuffExpanding universe

Space is big. And empty.

Chapter 1Our Place in the

Universe

How did we come to be?

Pg. 4

The Universe is Dynamic

Everything is moving

Some terminology:

Expansion

Revolve vs. Rotate

What motion does the Earth undergo?

What motion does the Sun undergo?

There are over 100,000,000,000 stars in our galaxy.

??

Thought QuestionSuppose you tried to count the more than 100 billion stars in our galaxy,

at a rate of one per second…

How long would it take you?

Unit Conversion

Convert 100 Billion seconds to years

Seconds -> Minutes -> Hours -> Days -> Years

Lookback Time

• We see objects as they were in the past:

• Light travels at a finite speed (300,000 km/s).

• The farther away we look in distance, the further back we look in time.

• Allows us to study the history of the Universe.

Example: Our nearest neighbor.

This photo shows the Andromeda Galaxy as it looked about 2 1/2 million years ago.

Question: When will be able to see what it looks like now?

M31, The Great Galaxy in Andromeda

Fig. 1.4

Light-year: the distance light travels in one

year.

(But how far is that?)

• Scientific Notation

• Multiply and Divide powers of 10

• Convert Units

• Rearrange an equation to solve for another variable

• Plug numbers in for variables in an equation and calculate

Math Skills Summary

• Scientific Notation– e.g. 300,000,000 = ?– e.g. 4x10-5 = ?

• Multiply and Divide powers of 10– e.g. 108 / 10-5 = ?

• Convert Units– e.g. How many inches in a mile?

• Rearrange an equation to solve for another variable– e.g. b = L / 4d2. Solve for d.

• Plug numbers in for variables in an equation and calculate– e.g. L = 3.8x1026 watts, d = 1.5x1011 m, b = ?

Math Skills Summary

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