Unit 1: Astronomy

Section 1: The Universe and Stars

The Universe

• The observable universe = anything we can observe. If the universe is 14 billion years old, we can only observe things within a 14 billion light year radius.

• Units of cosmic measurement:– Light years: 9.5 trillion km/yr - between galaxies/stars

– Astronomical Unit (AU) - within our Solar system

– Parsec: used to measure distance to objects outside the solar system but often in our galaxy

What is the Universe Made of?

- 73% Dark Energy - believed to

be acting against gravity and

causing the expansion of the

universe.

- 23% - Dark Matter - unique

matter that doesn’t emit light

or energy.

- 4% - Atoms - matter that makes

up all of the observable, visible

objects in the universe (stars,

planets, galaxies, etc.)

What is Light?

• Light is a form of electromagnetic radiation, which is energy that travels in waves.

• The electromagnetic spectrum organizes types of energy on a continuum based on wavelength

– Wavelength relates to the amount of energy

Which Color of visible light has longer wavelengths?

Which colors of visible light have shorter wavelengths?

What type of radiation has the shortest wavelength on the

spectrum?

What type of radiation has the longest wavelength on the

spectrum?

The Doppler effect

• The Doppler effect explained…Pay close attention! (up to 0:51)

• Check for understanding!

– What color(s) on the visible light spectrum would a star appear if it was moving toward Earth?

– What about if it was moving away from us?

How do we know what stars are made of?

• The emission spectrum– White light is actually a

combination of all colors

– When light passes through certain materials it is bent, different materials bend light into different patterns.

– Every element emits a unique spectra

• Therefore, we can match the spectra to the elements in the star!

Check for Understanding

Mystery star spectra: What is this star primarily made of?

Mystery star spectra: What is this star primarily made of?

Galaxies

Galaxy - group of millions or billions of stars, planets, gas, and dust held together by gravity

- Classified by their shape:- Elliptical- Irregular- Spiral

- Milky Way and Andromeda- We live in the Milky Way Galaxy!

Hertzsprung-Russell Diagram

• Plots the temperature versus luminosity (brightness) of stars

• Used to describe the life cycle of stars

• The longest stage of a star’s life is the main sequence.

Birth of a Star

• Stars are generally “born” in a nebula– Nebula: cloud of gas and dust– Stars are primarily comprised of Hydrogen and

Helium– When the temperature of the swirling gas

becomes high enough, nuclear fusion begins– The outward force from fusion reactions balances

with gravity pushing in = equilibrium of the star

Main Sequence of a Star

• Longest stage of a star’s life• Driven by fusion of hydrogen into helium• Can last from 10 million to hundreds of billions of

years! (prediction)

Leaving the Main Sequence

• Sun-like stars grow cooler and change to a red color.– Known as Red Giants

• Stars that are more massive than the sun will appear brighter as they grow larger

• Known as Supergiants

Death of a Star

• Red Giants generally have their outer layers of gas drift away and become white dwarf stars

• Supergiant stars undergo a catastrophic explosion called a supernova where they blow apart– What is left over is a super dense ball of particles

called a neutron star.– If a supermassive star explodes and leaves a core

too massive to form a neutron star, it can implode creating a black hole• Black holes draw light and energy from surrounding

stars