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UA / OTHER / ay 101 / What can we see with the given light out in space?

What can we see with the given light out in space?

What can we see with the given light out in space?


School: University of Alabama - Tuscaloosa
Department: OTHER
Course: Intro to Astronomy
Professor: Ronald buta
Term: Spring 2017
Tags: astronomy, study, guide, and exam
Cost: 50
Name: AY 101; Study Guide for Exam 1
Description: Covers Chapters 1 - 5, I added highlighted text for the super important things Prof. Buta said would definitely be on the test!
Uploaded: 02/06/2017
11 Pages 30 Views 5 Unlocks


What we can see with the given light out in space?

Exam 1 Study Guide





Covers Chapters 1-5

Lectures 1-2

● Space is the nothingness away from Earth and is intertwined with time ○ Time is determined using the Sun while on a planet

What are seasonal signposts?

○ “Today” is a concept relative only on Earth

● Time and space are intertwined in that what is happening “today” in the Universe cannot be seen due to the finite speed of light (670,616,629 mph)

○ In one year, a beam of light travels 6 trillion miles, and this is called a light year We also discuss several other topics like What is atomic orbital?

● “Observable Universe” is what we can see with the given light out in space; the Earth is approximately 14 billion years old, therefore we can only see 14 billion light years away

● The Solar System is 16 billion kilometers wide, or 100 Astronomical Units ○ An AU is the average Earth to Sun distance of about 93,000,000 miles ● Naked eye stars range from 10s to 100s of light years away 

Summer occurs when?

○ Meanwhile, galaxies can be 10s to 100s of millions of light years away ● The celestial sphere is an imaginary sphere against which all celestial objects project

○ The horizon only allows us to see half of it

○ The sphere seems to rotate, with stars continuously rising and setting relative to the horizon

1Don't forget about the age old question of How can one diagram the cell cycle indicating the timing of all processes?

● The celestial equator is an extension of our own equator on Earth; we can’t actually see a physical line that divides the Earth or the sphere but we know it is there

● Rising and setting motions are caused by Earth’s rotations 

Lecture 3

Celestial Phenomena

● Seasonal signposts: 

○ March 21 - March equinox (Northern Hemisphere spring) We also discuss several other topics like How should one be structuring an argument?

○ June 21 - June Solstice (N. Hem. Summer)

○ September 20 - Sept. Equinox (N. Hem. Fall)

○ December 21 - Dec. Solstice (N. Hem. Winter) Don't forget about the age old question of What is subcultures?

● Summer occurs when the sun is highest in the sky at noon, the days are the longest, and the nights are the shortest

● Winter occurs when the sun is lowest in the sky at noon, days are short, and nights are long

● At the time of an equinox, the sun crosses the celestial equator, day and night are equal length, and the sun rises due east and sets due west

Lunar Phases

● What are lunar phases? 

○ Every 29.5 days, the Moon cycles through a progression of different views of its day and night time sides; these are called phases

○ Phases are caused by the changing relative positions of the earth, moon and sun We also discuss several other topics like How is the present value of a growing annuity derived?

○ At each phase, the moon is in a different part of its orbit 

■ New moon means the cycle begins - moon rises at sunrise

2We also discuss several other topics like What is the meaning of production possibilities curve?

■ Waxing crescent

■ First quarter - moon rises at noon

■ Waxing gibbous (btwn half/full)

■ Full Moon - moon rises at sunset

■ Waning gibbous

■ Last quarter

■ Waning crescent - end of cycle, less than half the moon is visible ○ Phases are NOT caused by Earth’s shadow 

○ Eclipses are caused by Earth’s shadow, and these only happens during a full moon

■ Eclipses occur when one celestial body passes into the shadow of another. Eclipse phenomena occur regularly in the Earth-moon


■ Called a lunar eclipse when the moon passes into the earth’s

shadow; only occur at full moon

■ Solar eclipse is when the moon casts its shadow onto Earth; only occur at new moon

Lecture 5

Heliocentric vs geocentric model and the contributions of Kepler, Galileo, and Newton

● Two observations highlight why the heliocentric model is simpler ○ 1) Retrograde motion of mars

■ Heliocentric view - retrograde is an illusion

■ When earth catches up to mars, our motion makes it seem

like it is going backwards

○ 2) Mercury and Venus only seen just before sunrise or just after sunset ■ How do you prove that earth is moving? Look for stellar parallax ■ The Greeks could not detect these parallax and concluded the

Earth was not moving


■ They couldn’t see that the stars appeared to be

moving in the night sky

Kepler’s Laws of Planetary Motion 

● Empirical and based on Tycho Brahe observations

○ Law 1 - Shape of orbits (ellipses)

■ Planets orbit the Sun along elliptical paths with the Sun at one focus ■ The degree to which an orbit is elliptical is called the eccentricity, or e

■ e = 0 (circle); >1 (very elliptical)

○ Law 2 - Speed along orbits

■ As a planet moves around its orbit, it sweeps out equal areas in

equal times

■ To do this, a planet travels its fastest at perihelion and slowest at aphelion

○ Law 3 - relation between orbit sizes and orbital periods

■ p = period in years

■ a = semi-major axis radius in AU

■ These two orbits have the same a and hence the same orbital period ■ Orbital period depends only on a not e


● His observations supported Copernican revolution

● His observations of the phases of Venus proved that it orbits the Sun and not Earth 


How did Newton change our view of the universe?

● What is gravity? 

○ force derived from matter

○ acts at a distance

○ one of four fundamental forces of nature

○ always attractive

○ Universal Law of Gravitation 

■ Every mass attracts every other mass 

■ Attraction is directly proportional to the product of their masses ■ Attraction is inversely proportional to the square of the distance btwn their centers 

○ Law of Gravitation tells us

■ why planetary orbits are elliptical; because of the inverse square law of gravity

■ why planets move faster at perihelion than at aphelion; because the gravitational force pulls along the line joining the planet and the sun ■ why planets farther from the sun move more slowly than those

closer to it; also inverse square law

■ How fast something must move to achieve a circular orbit and how fast it must go so it can escape another object (called the escape


Lecture 6/7 (Same topics discussed in both)

Intro to Telescopes

● Telescope is a mechanical device designed to collect and focus light


○ Its three functions are to make faint objects easier to see, resolve fine details, and magnify images

○ There are reflector telescopes and refractor telescopes

Formation of Celestial Objects

● Definitions of important concepts 

○ Accelerated motion - when velocity is changing (speed, direction, or both) ○ Velocity - the speed and direction of a moving object

○ Uniform motion - motion in a fixed direction at a constant speed ○ Force - an action that serves to accelerate and object

○ Mass - amount of material in an object

○ Weight - force of gravity on an object on the surface of a world

● The acceleration of gravity does NOT depend on mass! 


● What is energy?

○ Energy is a physical property associated with motion, heat, light, etc.; To put it simply, energy is needed to do things! 

○ There is kinetic energy (motion), potential energy (stored), and radiant energy (light)

● Conservation of energy

○ Energy can’t be created or destroyed, only changed from one form to another 

■ e.g Gravitational potential energy can be converted into thermal kinetic energy, or heat

■ Temperature is the measure of the average random speeds of

particles in a substance

● Conservation of angular momentum


○ Angular momentum is the property of any object that is rotating or moving along a curved path (like an orbit) 

○ Many phenomena can be linked to this law of conservation; such as the rapid rotation of a neutron star, the planets orbiting the sun in one plane, and disk-shaped galaxies

● Newton’s 3 Laws of Motion 

○ Law 1 - in the absence of any external forces, an object at rest remains at rest and an object in uniform motion remains in uniform motion

○ Law 2 - Force = Mass x Acceleration

■ m = mass of man

■ M = mass of Earth

■ F = gravitational force btwn Earth and man

○ Law 3 - Forces only come in pairs; For every action force, there is an equal and opposite reaction force

● How do celestial objects form? 

○ They start with an interstellar cloud of gas and dust

○ Scattered among gases, there will be pockets that are very cold, dusty, and much more dense than other areas

○ Gravity draws the material closer together in the pocket, IF it can overcome random thermal motions in the pocket; And if gravity wins, then

gravitational collapse begins while spinning it faster and faster

○ How does gravity cause tides? 

■ The gravitational attraction to the Moon is weakest on one side of Earth, and strongest on the other side; So the difference in

gravitational attraction tries to pull Earth apart, raising tidal bulges

both toward and away from the Moon


Lecture 8

Basic Properties of Light and Matter

● Atoms and Molecules

○ Electromagnetic forces bind electrons and atomic nuclei into atoms, atoms into molecules, and molecules into substances.

○ Electromagnetism is the general term for the forces involved between charged particles 

○ Charge is an intrinsic property of matter

■ opposite charges attracts, and like charges repel

■ It generates electric force fields, and the random motion of charged particles disturbs these fields

■ Electric field waves induce magnetic field waves, this results 

in an electromagnetic wave, which we perceive as light 

■ Electromagnetic waves can be characterized in terms of the

wavelength, or distance between successive peaks

■ In visible light, wavelength determines colour 

■ Any wavelength is possible, but there’s only one speed: 670

MILLION mph in vacuum, independent of wavelength. A

vacuum is empty space.

○ Photons

■ A photon is a particle of light that carries the energy of an 

electromagnetic wave; e.g. longer wavelengths mean lower energy,

and shorter wavelengths mean higher energy

■ The whole range of possible wavelengths is called the

electromagnetic spectrum; We can only see the visible portion

■ The spectrum is broken up into sections with specific names

and is organized from most dangerous on the left to safest

on the right, with the visible portion in the middle


○ Thermal Radiation 

■ The light emitted from any relatively dense solid, liquid or gas is due to the random thermal motions in the material; Everything radiates thermal radiation!

■ At absolute zero (0K), all random thermal motions cease

■ Rules of thermal radiation: 

■ 1. The shape of the spectrum depends only on the

temperature of an object

■ 2. If the temperature of an object is increased it will emit

more light at all wavelengths compared to when it was cooler

■ 3. If an object’s temperature is increased, the wavelength of

the max intensity in its spectrum will decrease. Meaning

hotter objects emit more photons of higher energy/shorter

wavelengths than cooler objects; e.g. cool stars appear

reddish, and hot stars appear bluish-white

Lecture 9

Emission and Absorption Line Spectra & The Doppler Effect

● Spectroscopy is the scientific study of dispersed light

○ Glass prisms are great examples of an object that disperses light ○ Three types of spectra 

■ Continuous spectrum

■ The intensity varies smoothly with wavelength

■ Any hot, dense solid, liquid, or gas emits this type of


■ Pure thermal radiation spectrum is of this type

■ Emission line

■ Intensity of the light is discontinuous and concentrated in

discrete bright lines


■ Hot, low density gas viewed against a dark background has

this kind of spectrum

■ Absorption line

■ Intensity mostly continuous, but interrupted by dark

absorption lines

■ Visible when you view a hot, dense, continuous source

through cooler, lower density gas, like an interstellar cloud

■ All normal stars have this kind of spectrum

■ e.g. Stars emit continuous thermal radiation, but this

light is viewed through cooler, lower density gases in

their atmospheres. They radiate all colors, but the

gases in their atmospheres suppress them and

selectively show what colors they emit.

■ Emission and absorption lines are tied to atomic structure 

■ Standard atomic model consists of a central nucleus with

protons and neutrons

■ Each electron occupies an orbital position, or energy level

■ “Quantum Leaps” between levels lead to emission and

absorption of light and energy, respectively

■ Downward leaps into smaller orbital positions lead to

an emission of a photon

■ Upward leaps into higher orbital positions occur after

absorption of a photon

○ Detecting movement

■ The Doppler Effect refers to small shifts in the wavelengths of 

spectral emission and absorption lines due to the motion of an 

object through space. 

■ Shifts are detected through reading spectra

■ Motion away produces redshifts

■ Motion towards produces blueshifts

■ Using the Doppler Effect we can detect


■ The rotation of the Milky Way and other galaxies

■ The expansion of the Universe

■ The presence of planets orbiting other stars

○ Dangerous radiation from space is filtered through our atmosphere ■ All X-ray and gamma ray light is absorbed very high in the


■ UV light is mostly absorbed by the ozone (O3), but some still

penetrates through and can cause sunburn

■ The atmosphere is transparent to visible light, some IR, and radio waves


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