1. UNIT XVI: ASTRONOMY

2. The universe is vast. Incredibly, incredibly vast
The universe is vast. Incredibly, incredibly vast. 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.

3. Scaling the Universe
The true dimensions of the universe are unknown, but it is commonly said 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

4. 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

5. 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

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

7. Evidence for the Big Bang
The Big Bang is supported by two pieces of evidence:
Cosmic background radiation
Red-shift of visible light

8. To understand the evidence supporting the Big Bang, you must first understand radiation traveling through space.
Radiation travels in waves
Shorter wavelengths = higher energy
Wavelengths of radiation can be stretched or compressed

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

10. 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 is evidence that this matter was once together at a singularity

11. 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 collapse 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

12. 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

13. 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

14. 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

15. Terrestrial Planets
Mercury
Venus
Earth
Mars
Jovian Planets
Jupiter
Saturn
Uranus
Neptune

16. Other Components of Our Solar System
Comets (primarily ice and dust)
Asteroids (rocky and metallic)
Impact evidence is recorded in the geologic record along with mass extinctions

17. Additional Solar System Data
Found in the ESRT

18. Our moon is critically important to life here on Earth
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.

19. 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

20. 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.

21. 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
Tides are about 6 hours apart (high to low)

22. 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