AST101- Chapter 1

What is astronomy?

The study of the objects that go beyond Earth and the processes by which these objects interact with one another.

What is a hypothesis?

A proposed explanation that can be tested with experiments. If experimental results are inconsistent with the hypothesis, a scientist must discard the hypothesis and try to develop an alternate one.

Scientific Laws

The universal "rules" that everything in the universe plays by, deduced by scientists over centuries.

Speed of Light

3×10^8 m per second

Look-Back Time Principle

The farther out in space we look, the longer light has taken to get here, meaning we are seeing the object as it was the longer ago it left its place of origin. This allows us to reconstruct the history of the cosmos and understand how it evolved over time.

Astronomical Unit (AU)

The average distance from Earth to the Sun. It is approximately 150 million km.

How long does light take to travel to earth?

8 minutes

Earth's Orbital Speed

Earth travels 110,000 km/h to orbit the Sun within a year.

Definition of a Planet

A body of significant size that doesn't emit its own light.

Methods for Finding Exoplanets

Planets orbiting other stars are found primarily by observing the pull their gravity exerts on their stars OR from the light they block from their stars when they are in front of them (transit).

Source of Visibility for Nearby Planets

We can see the nearby planets in our skies because they reflect light off the Sun

Multi-Star Systems

Although the Sun is a lone star, many stars are born in double/triple systems with two, three, or more stars revolving about each other.

Nearest Star (Distance)

The nearest star is 4.25 light-years away.

Andromeda Galaxy (M31) Details

The nearest large galaxy. It is approximately 2 million light-years away.

Local Group

The cluster of approximately 50 galaxies that includes both the Milky Way and the Andromeda Galaxy.

Sun's Position in the Galaxy

The Sun is 30,000 light years away from the center of the galaxy.

Galaxies Visible from Earth (Estimate)

There are approximately 1 trillion galaxies visible from Earth, with each galaxy having around 100 billion stars.

Millennium Simulation

A computer simulation of the matter distribution in the universe.