Astronomy101: #C01 - Astronomy Lingo

Title        : Astronomy 101

ISBN        : 9781440563591

Author    : Carolyn Collins Petersen

A Crash Course In The Science Of Space

From the Sun & Moon to Wormholes & Warp Drive, Key Theories, Discoveries, And Facts about the Universe. 

Astronomy101: Chapter 1 Astronomy Lingo

In this chapter, Author is trying to introduce us some terms that has been used in astronomy field, so that we can understand easily about the topic discussed in future chapter.

DISTANCE

     First, let us talk about unit used in astronomy.

• In Solar System
• Unit : AU (Astronomical Unit)
• 1 AU define distance between Earth & Sun
• 1 AU = 149 million km = 93 million miles
• Example:
• Jupiter 5.2 AU from Sun = 149 million km * 5.2 
                                              = 774.8 million km
• In Interstellar Space 星际
• Unit : ly (light-year)
• 1 ly = v _light * Total Second In a Year
                   = 300,000 km/s * 31,536,000 s
         = 9.5 trillion km
• Can represent a very huge number, easier to describe the distance in interstellar space.
• Example: 
• 4.2 ly away from us = 4.2 * 9.5 trillion km
• Unit : pc (parsec)
• 1 pc = 3.26 ly
• Example:
• Famous Pleiades star cluster is 150 pc away
• Nearest Spiral Galaxy (Andromeda Galaxy) is 767 kpc away
• Unit : Mpc (Mega parsec)
• Example:
• Nearest Galaxies cluster in Milky Way Galaxy is 16 Mpc away
• Unit : Gpc (Giga parsec)
• Is the largest unit being used

LIGHT

    Speed of light in

1. Vacuum
• c = v_light = 299,792,458 m/s 
2. Water
• c = v_light = 299,600,000 m/s

• Not only defined distance but also give us an idea about the age of universe.
• For example:
• The moon that we currently seen is 1.28 second old.
• The sun that we currently seen is 8.3 min old.
• Closest star (Proxima Centauri) is 4 years old.
• Light from a galaxy is 65 million ly ago.
• Which also mean it left that galaxy when dinosaur is facing extinction.
• There are several quote I love when reading this book.

"When you look out in space, you're looking back into time." 

 "Farther across space you look, the further back in time you see."

"Telescope / Instruments study cosmos = Time Machines " 

 

    Visible Light

1. Red
2. Orange
3. Yellow
4. Green
5. Blue
6. Indigo
7. Violet

    Spectra & Spectroscopy 

• Both are important tools in astronomer's kit.
• Slice into component wavelength.
• Result in spectrum. (Some sort like prism)
• There are more colors in spectrum that we can't see.
• Spectroscopy:
• Let us know how fast / slow an object is moving.
• So we can figure out how far away it is.
• 2 important terms (Redshift & Blueshift):
  
• Redshift often used to indicate object's distance, Redshift = 0.5, means distance = z = 0.5.
• So why Redshift is used to calculate distance in universe.
• I found a very good explanation video about Redshift from Astronomic YouTube Channel. I have do some screenshot & summary based on the video.
  
  Picture 1 & 2
1. First, let us talk about sound. 
2. When a police car is moving, the siren sound  heard in front of the vehicle is compressed.  This create a high frequency sound.
3. Siren sound  heard at the back of the vehicle is stretch out.  This create a lower frequency sound.
4. So for the case in sound we look at frequency, but in light we look at the wavelength.
   Picture 3 & 4
5. Universe is expanding, further away a galaxy, faster the rate its moving.
6. More light is red shifted.
7. Measure amount of redshift is great way to measure the distance from the Earth.