UNIT 2: ASTRONOMY

After UNIT 2 you should be able to:

o Understand scaling: solar system, galaxy, universeo Understand that we are a part of a spiral galaxy known as the Milky

Wayo Know the approximate age of the universe and solar systemo Understand the Big Bang theory and supporting evidence such as

cosmic background radiation and red-shift of lighto Understand the process of fusion taking place in the Suno Understand how the solar system formed, what layered the planets,

and how they were separated into two distinct groups: Jovian and Terrestrial

o Differentiate between a comet and an asteroido Understand how moon phases are observedo Understand the difference between the sidereal period and synodic

period of the moono Understand what impacts the formation of high and low tideso Differentiate between lunar and solar eclipseso Use the Electromagnetic Spectrum, Characteristics of Stars, and Solar

System Data charts in the ESRT

UNIT 2 vocabulary you should be able to use and understand:

o Universeo Staro Suno Solar systemo Galaxyo Milky Way galaxyo Spiral galaxyo Singularityo Big Bang theoryo Cosmic background

radiationo Radiationo Visible light o Wavelengtho Electromagnetic

spectrumo Red-shifto Blue-shifto Doppler Effect

o Luminosityo Supernovao Massiveo Giant staro White dwarfo Main sequence staro Fusiono Atomso Gravityo Densityo Terrestrial planeto Jovian planeto Gas gianto Period of revolutiono Period of rotationo Equatorial diametero Eccentricityo Masso Moon

o Cometo Asteroido Impact cratero Celestial objecto Sidereal periodo Synodic periodo Waxingo Waningo Crescento Gibbouso Tideso High tideo Low tideo Spring tideo Neap tideo Solar eclipseo Lunar eclipse

The universe is vast. Incredibly, incredibly vast. Even with modern technology, humans are unable to leave even our solar system within the timeframe of their lives. Astronomy is therefore much more abstract and theoretical than other disciplines here on Earth.

Scaling the Universe

The true dimensions of the universe are unknown, but it has been said (in an expression) that there are as many stars as grains of sand on all the beaches of the world.

Our solar system surrounds a star known as the Sun

Our solar system is a part of many solar systems that make up the Milky Way galaxy

Galaxies

Galaxies take on a variety of shapes

The Milky Way is known as a spiral galaxy, with our solar system located in one of the outer arms

There are billions of galaxies that make up the visible universe

Age of the Universe

Our universe is estimated to be about 13.7 billion years old

This estimate is based on the projected expansion from a singularity (single point) based on current evidence

The Big Bang

The Big Bang is the current accepted theory for the expansion of the universe

Approximately 13.7 billion years ago there was a rapid expansion and differentiation of matter that created the universe

Evidence for the Big Bang

The Big Bang is supported by two pieces of evidence:

Cosmic background radiation

Red-shift of visible light

To understand the evidence supporting the Big Bang, you must first understand radiation traveling through space.

Electromagnetic radiation travels in waves

Shorter wavelengths = higher energy

Wavelengths of radiation can be stretched or compressed

Cosmic Background Radiation

Radiation exists from an undefined source, believed to be from a time period following the Big Bang

Red Shift of Visible Light

Light from distant sources that are moving away from an observer experiences stretching in the wavelength towards the red end of the spectrum

Light from distant galaxies is red-shifted so they are moving away

This phenomenon of wavelength alteration is known as the Doppler Effect

When an object is moving towardsan observer, the waves are compressed and it is blue-shifted

This is evidence that this matter was once together at a singularity

Stars

Our Sun is a medium-sized yellow star

Stars are classified by luminosity, color, and size

Larger stars have a short lifespan and can explode in a violent supernova

We see stars in the night sky that have burned out long ago but their light is still traveling towards us

Fusion

The process of fusion unites lighter elements and produces heavier ones releasing massive amounts of energy

Hydrogen atoms fuse into helium inside of our Sun heating Earth 93 million miles away

The Beginnings of Our Solar System

Our solar system is approximately 5 billion years old.

The force of gravity caused fragments of debris to begin clumping together within a spinning disc

Our Sun would later begin the process of fusion in the center of the spinning disc

8 Planets

8 planets would form within this spinning disc

The densest material was closest to the Sun

This formed rocky, denser planets known as the Terrestrial planets

The less dense, gaseous, and icy Jovian planets formed beyond the asteroid belt

Terrestrial Planets

Mercury Venus Earth Mars

Jovian Planets

Jupiter Saturn Uranus Neptune

Other Components of Our Solar System

Comets (primarily ice and dust)

Asteroids (rocky and metallic)

Impact evidence is recorded in the geologic record (as craters) along with mass extinctions but erosion and deposition have erased many craters on Earth

Additional Solar System Data

Found in the ESRT

Our moon is critically important to life here on Earth. In addition to our tides, the moon is responsible for maintaining Earth’s rate of rotation.

The Moon

The Moon revolves around Earth once every 27.3 days (sidereal period)

Coincidentally, the moon’s period of rotation is equal to its period of revolution meaning that we will only ever see one side of the moon

Moon Phases

The Moon enters phases as it orbits Earth based on how we view the lit side of the moon

The time for the moon to go through all phases once is slightly longer (29 days --- the synodic period) than its orbit due to Earth’s revolution around the Sun.

Tides

The Moon exhibits gravitational pull on the Earth

This pull bulges water towards the Moon as well as on the opposite side of the Earth (high tide)

When the Sun, Moon, and Earth are aligned, the tides are the highest and the lowest on Earth (spring tides)

The Moon has a more significant influence on tides even though it is smaller than the Sun because it is closer to Earth

Tides are about 6 hours apart (high to low)

Eclipses

Eclipses are named for the object that is being blocked from an Earth perspective

Solar eclipse: Sun is blocked by the moon

Lunar eclipse: the Moon is blocked from the Sun’s rays by the Earth