Chapter 5

The Earth-Moon System

The Tools of Astronomers

What is Astronomy?

• The branch of science that deals with “what’s up there”.

• The study of the universe• Planets, galaxies, stars

Astronomers• Someone who observes the universe and tries

to explain what was observed.

• Different astronomers study different parts of the universe.

• There are professional (for career) astronomers and amateur (for enjoyment) astronomers.

Why we study astronomy• Mostly for enjoyment• People want to know and learn more about the

universe.• Stars can be beautiful to look at

• Also for benefits• Navigators use their knowledge of a star’s

position to tell direction.

Tools of Astronomy• Eyes • Can be used to observe day and night• Can observe the position of some planets and

stars• Can observe the position of the sun and moon in

the sky• *Do not look directly at the sun, it can harm your

eyes.

• Telescopes• A device that collects light• Makes distant objects appear closer and larger• Most of what we know about the stars and

planets comes from telescopes

• Robots and humans in space• Both have been to the moon• Only robots have been sent to study other planets

Models, Theories, Hypotheses

• Models• They simplify the world so we can understand it

better. • Example: Earth is not exactly a sphere, but we use a

sphere as a model of Earth.

• Theory• A well-tested scientific explanation supported by

evidence• Allows us to make a prediction about a scientific

event or idea.• Example: The theory of gravity explains the past motion

of planets and allows us to predict their future motion.

• Theory (cont.)• The more evidence found through observations,

the more a theory’s certainty increases.• Can never be proven without complete certainty.• Science can only tell what is likely, not what is

certain.• If new evidence does not support a theory, the

theory must be changed

• Hypothesis• A scientific explanation that has not yet been fully

tested.