Exam #1 Study Guide

(Note this is not all the information you need to know for the test, these are just SOME of the main points)

Moon Phases

• Moon is always ½ illuminated by the Sun, and the sunlit side ALWAYS faces the sun

• New Moon is when the moon is between the Earth and Sun, it is highest in the sky at noon. The New Moon is the only time a solar eclipse can happen.

• Full Moon rises at sunset, and sets at sunrise. A lunar eclipse can happen during a full moon.

• Waxing (“increasing”) • Waning (“decreasing”)• Order: New Moon, Waxing crescent, first quarter moon,

waxing gibbous, full moon, waning gibbous moon, third quarter, waning crescent --- REPEAT next month

Eclipses

• Lunar eclipse- occurs when the earth “shades” the Moon as it passes between the moon and sun, during a full moon

• Solar eclipse- occurs when the moon passes in front of the sun, blocking the sun from view from earth, during a new moon

Newton’s Laws

• 1. the law of inertia, a body remains at rest, or moves in a straight line at a constant speed unless acted upon by a net outside force. (an outside force would be something exerted on the body other than your body itself)

• 2. F=ma the acceleration of an object is proportional to the net outside force acting on the object. (the harder you push on an object, the greater the resulting acceleration)

• 3. Whenever one body exerts a force on a second body, the second body exerts an equal and opposite force on the first body. (Standing on the ground, you weigh 110 pounds, the floor is pushing up 110 pounds, equal force)

Newton’s law of Gravity

• Fgravity = G (m1m2/r2)

• G = gravitational contast

• m = masses of the two objects

• r = the distance between the two

• Ex: How much would you weigh on a planet that has the same mass as Earth but has ¼ the radius (r)?

– (Answer on next slide)

ANSWER

• You would weight 4 times more than you do on Earth

Gravity

• Newton’s law of gravity explains why the planet rotate the sun in a elliptical manner without falling out their orbits

Diurnal motion

• Diurnal- means having a period of ONE day• Stars rise in the east, and set in the west• The diurnal, or daily motion of the stars occurs

b/c the earth rotates once a day around an axis from the north pole to the south pole

• The stars will slowly shift throughout the year, approximately FOUR minutes EARLIER each night.– This is because of the rotation of the Earth around the

Sun

Seasons

• The sun heats the Earth’s surface• The closer the sun the warmer the surface• It is NOT Earth’s orbital eccentricity that effects the seasons• The seasons are caused by the 23 ½ degree tilt of the earth• The sun stays high in the midday sky in summer• The sun is low (not as direct) in the midday in the winter • March 21- sun crosses northward across celestial

equator at the vernal equinox and marks beginning of spring,

• -Sep. 22- sun moves southward across celestial equator called autumnal equinox

• When observed from one night to the next, a planet appears to move from West to East against the background stars most of the time.

• Sometimes it will appear to reverse direction. For a short time, it moves from East to West against the background constellations.

• This reversal is known as retrograde motion. All planets exhibit this behavior as seen from Earth. It is due to the relative motion of Earth and the planet.

Retrograde motion of planets

Blackbody radiation• A perfect blackbody does not reflect any light at

all, it absorbs all light. The Sun is an example of blackbody radiation

• The higher an objects temperature, the shorter the wavelength (Wein’s Law)

• Stefan- Boltzmann law states that a blackbody radiates electromagnetic waves with a total energy flux (F) directly proportional to the fourth power of the Kelvin temperature (T) of the object

• Engery flux is how rapidly energy is flowing out of the object• The amount of energy emitted by a blackbody depends on

both its temperature and its surface area (the larger the object, the more heat it will radiate)

The Sun is like a Blackbody

Question

• If you double the temperature of an object from 300K to 600K, what would be the energy emitted from the object’s surface each second?

Answer

• Each second would increase by a factor of 2, therefore 24= 16 (Stefan-Boltzmann law)

Telescopes

• A refracting Telescope- consists of a large diameter objective lens witha longfocal length and a small eyepiece lens of short focal length. the eyepiece lensmagnifies the image formed by the objective lens in its focal plane.(astrnomers want to view an image so they add a second lens to magnify the imageformed in the focal plane, called a refracting telescope or refracting)

Telescopes continued…• Angular resolution- The angular resolution of a telescope indicates

thesharpness of the telescopes image. To determine the angular resolution of atelescope pick out two adjacent stars whose separate images are barelydiscernible the angle between the stars is the telescopes angular resolution,the smaller that angle the finer the details can be seen and the finer theimage.

One factor limiting angular resolution is diffraction which is the tendency oflight waves to spread out when they are confined to a small area like the lensor mirror of a telescope.

Magnification• The amount of magnification depends on the focal length of the

primary and the eyepiece (The smaller the eyepiece, the greater the magnification)

Kirchoff’s Laws• A hot opaque body (blackbody)

produces a smooth continuous spectrum– Example: stars

• A cool transparent gas in front of a source of a continuous spectrum produces an absorption-line spectrum– Example – planetary

atmospheres, solar photosphere and chromosphere

• A hot transparent gas radiates an emission-line spectrum (against a dark background)– Example: the solar corona

Ancient Astronomers

Ancient astronomers knew that the earth was a sphere and believed it was the center of the universe

• Aristotle dismissed the heliocentric system he saw because he saw no parallax

• Believed the heavens were unchangeable

Copernicus

• (1473-1543) – Polish scientist who Re-proposed heliocentric theory and put the Sun at the center, but still believed the orbits of the planets were circles + epicycles

• Heliocentric Model

Ptolemaic system• Thought of by Ptolemy. Ptolemy (127- 145ad) -

Egypt -Used the concept of Epicycles to explain the motion of the Sun and planets

• Said that each planet moved in a small circle, or an epicycle, whose center turns in a larger circle (the deferent), rotating counterclockwise

• Theory is flawed!

Tycho Brahe

• (1546-1601), Danish

• -Observed a supernova, and

periodic comets

• – Proof that the stars and planets are not constant, as the ancient astronomers believed

• -Best pre-telescope observer

Galileo

• (1564-1642), Italian • -Used telescope to view Jupiter’s moons, lunar mountains, and

sunspots• – Phases of Venus• • Experiments on motion• – Including attempts to measure the speed of light• – Famous gravity experiment using the leaning tower of Pisa• -Galileo also discovered four moons, now called the Galilean satellites,

orbiting Jupiter• Phases of Venus- Galileo’s observations of Venus’s gibbous (“full-ish”)

phase definitively ruled out Ptolemy’s geocentric model • Galileo discovered that the higher an object is dropped, the greater its

speed when it reaches the ground• - All falling objects near the surface of the Earth have the same

acceleration (9.8 m/s2)• -The acceleration of gravity on the surface of other solar-system bodies

depends on their mass and radius

Kepler’s Laws• 1. The orbits are ellipses

– - The planets move about the sun in elliptical orbits with the Sun at one foci of the ellipse

– - The Semi-major axis is ½ the “long” width of the ellipse– - Eccentricity – a measure of how oblong an ellipse is.

• 2. A planet’s speed varies as it moves around its elliptical orbit

– - The Planet sweeps out equal areas of the elliptical orbit, in equal time intervals

– - The planet moves fastest when it is closest to the Sun and slowest when it is farthest away

• 3. The orbital period of a planet is related to the size of its orbit

– - The square of a planet’s period (P) is proportional– - To the cube of its semi-major axis (a).– - The farther a planet is from the sun, the longer it– takes to go around the sun– P2 = A3 P= period (in years)– A= semi- major axis (in AU)– only applies to planetary motion about the sun

Isaac Newton

• (1642 – 1727)• Developed the Laws of Motion• Discovered the law of gravity• Used physics to derive Kepler’s 3rd

Law

Units

• Common Units Used: • Distance- AU for between planets, 1AU=distance from

earth to sun• Km- size of features on planets• Mass- kg• *mass is different from weight, weight is force exerted by

gravity• Speed- km/s• Speed of light: 3 x 108 m/s• Temperature- Kelvin, Centigrade, and Fahrenheit • Distance Traveled= speed x time• D=vt

Planet order• Layout of the Solar System starting from sun- Mercury, Venus ,

Earth , Mars , Jupiter , Saturn , Uranus , Neptune , Pluto

Terrestrial planets

• The first four are Terrestrial Planets which are set apart because they aresmall, rocky materials containing iron, oxygen, silicon, magnesium, nickel, andsulfur. with high density.

Jovian planets

• The outer four are the Jovian Planets which are large and mostly composed ofhelium and hydrogen are have a low density.

Question

• What does it take for a planet to have active volcanoes?

Answer

• -requires heat hot after planet formed- Big planets cool slower- Big terrestrial planets are active longer- Fewer craters- more likely to have active volcanoes

Question

• What does a planet need to have an atmosphere?

Answer

• -Requires Gas-gas must be cool enough to not escape-must have enough gravity-Big cool planets are more likely to have an atmosphere