PHYS 1055 Study Guide - Fall 2018, Comprehensive Midterm Notes - Time, Sun, Solar System
PHYS 1055
MIDTERM EXAM
STUDY GUIDE
Fall 2018
Chapter 1 Textbook Notes
A Modern View of the Universe
1.1 The Scale of the Universe
Our Cosmic Adress
• The galaxies seen in the Hubble Telescope are several key levels of structure in the
universe known as the cosmic address
• A galaxy is a great island of starts in space all held together by gravity and orbiting a
common center
• Our solar system is located half way through the center to the edge of the galactic disk
• Our galaxy is one of the two largest among more than 70 galaxies, most are small and
make up the Local group
• Groups of galaxies with many more members are called galaxy clusters
• The regions in which galaxies and galaxy clusters are tightly packed are called
superclusters
• Our local group is located in the outskirts of the Local Supercluster
• Therefore the universe is the sum total of all matter and energy encompassing the
superclusters and voids and everything within them
Astronomical Distance Measurements
• 1 kilometer = 0.6 miles
• One astronomical unit (AU) is the unit used to suggest the Earth’s average distance from
the Sun, which is about 150 million kilometers (93 million miles)
• One light-year (ly) is the distance light can travel in 1 year which is about 10 trillion
kilometers (6 trillion miles), generally use light years to describe the distance of stars and
galaxies
o Light year is a unit of distance, NOT TIME
o Light travels at the speed of light (300,000 km/sec)
• 1 parsec (pc) = 1.9 * 1013 miles (19 trillion miles = 3.26 light years)
• Betelgeuse = 642.5 light years away
• Bellatrix (250 light-years away)
• Rigel (860 light-years away)
• Orion Nebule ( 1,344 light-years away)
• GN-z11 The most distant known galaxy to date
o 13.39 Gigalight years = 13.39 billion light years
o We are seeing the universe as it was when it was only ~400 million years old
Looking Back in Time
• Light takes more than 1 second to reach Earth from the Moon
• 8 minutes to reach Earth from the Sun
• Stars are so far away that their light takes years to reach us
• Sirius is the brightest star which is located 8 light years away
• It takes light 8 years to travel this distance, therefore when we see Sirius it not seen as it
is today but rather as it was 8 years ago
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Chapter 1 Textbook Notes
• Orion Nebula is located 1350 light years from Earth, therefore we see it as it is 1350
years ago
• The Andromeda Galaxy is about 2.5 million light years away which means we see it as it
looked about 2.5 million years ago
• Andromeda galaxy is also 100,000 light years in diameter, the light we see from the far
side of the galaxy must have left its joury to us 100,000 years ago before the light we see
from the near side
The Observable Universe
• The measured age of the universe is about 14 billion years
• This distance of 14 billion light years therefore marks the boundary (or horizon) of our
observable universe
• We simply cannot see or study anything beyond the bounds of our observable universe
because the light from such distances has not yet had time to reach us in a 14 billion year
old universe
The Scale of the Solar System
• To imagine the size of the solar system we will shrink it to a more depictable size
• It is scaled to one ten-billionth of its actual size and distances
• Voyage scale Model
• It shows the sun and planets at their correct sizes (but NOT distances)
Distances to the Stars
• Roughly 600 meter distance from the Sun to Pluto
• A light-year is about 10 trillion kilometers which becomes 1000 kilometers on the 1-to-
10 billion scale (because 10 trillion/10 billion = 1000)
• The nearest star system to our own is Alpha Centauri is about 4.4 light years away
• The distance is about 4400 kilometers (2700 miles) (distance across the US)
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