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Astronomy Exam #1


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1 Astronomical Unit
93 Million miles

1 AU = distance from sun to earth
path sun travels in one year
Andromeda Galaxy
Farthest object naked eye can see

2.2 Mly away
Circumpolar Constellations
Never Rises, Never Sets
Plane of equator and ecliptic are ____ degrees apart
23 1/2
Gravitational force from sun and moon make the axis change it's tilt at times -- makes the spin axis go around in a circle
Rotation of the earth on its spin axis.

One day.
Rotation of earth around the sun.

One year.
We always see the same side of the moon. Why?
Moon rotates once on its spin axis in the same time as it revolves once around Earth.
New Moon
Completely dark.
Quarter Moon
Half lit up
Full Moon
Completely lit up
Waxing moon
crescent or gibbous getting bigger between new moon and quarter moons
Waning moon
crescent or gibbous getting smaller
Sidereal Period
Time for the moon to go once around relative to the STARS
Synodic Period
New moon to new moon

Earth has moved. Have to go further to catch back up to sun and get all three object lined up the same way.
Lunar Eclipse
Moon covered up by Earth
Solar Eclipse
Sun covered up by moon
Lunar eclipses only occur with a _____ moon.
Fully eclipsed moon is ________ in color
Lunar eclipses take about ____
Six hours
A solar eclipse in totality last only _______
2-3 minutes
Can see _______ and _______ when photosphere is covered during eclipse.
chromosphere and corona
Annular Eclipse
Partial Eclipse
Line of Nodes
Where planes of orbit of earth and moon cross

Line of nodes must point at sun for an eclipse
From Lunar Eclipses the ancient Greeks knew ________
the earth is a sphere

due to earth's shadow cast on the moon
Figured out circumference of the earth
Aristarchus of Samos
Thought he figured out distance to sun - 20 times distance to the moon.

First person to predict the sun was the center of the solar system.
Cannot be seen with naked eye - only with telescope.
Distance to the nearest star
1 parsec
Naked Eye Planets
Non-naked Eye Planets
Planets are found in a 16 degree band around the ______
Retrograde Motion
Reverse Motion

Planets at their brightest

Due to differing speeds
_____, ______, ______ can be found anywhere on the ecliptic relative to the sun
Jupiter, Mars, Saturn
_______ never more than 28 degrees from the sun
_____ never more than 47 degrees from the sun
Apparant Magnitude
brightness of an object

Negative magnitudes: more negative, brighter
North Celestial Pole moves about 1 degree every 70 years due to ______
Planet as far from sun as it could possibly be (as it appears from Earth)
the configuration of a planet when it appears opposite the sun in the sky
the arrangement of a planet in the same part of the sky as the sun
For the outer planets, retrograde motion occurs at _________.
Thales of Miletus
The universe is a rational place and the human mind can understand the way it works.
Mathematics is the way to understand the universe.

Greeks were big on symmetry.
Uniform Circular Motion for objects in the sky
Built first model of the universe with spheres moving in Uniform Circular Motion
Earth is changeable and imperfect; the heavens are permanent and perfect.

Earth is at rest at the center of the universe (Geocentric Model)
Made a systematic catalog of about 850 stars.

First person to notice Precession.

Divided stars into brightness ranges - magnitude.
Mag 1 - Brightest
Mag 6 - Dimmest
had the confusing stupid model of the planets.

Earth in the center of the universe

Compendium of Greek Astronmical Knowledge
Sun-centered solar system (Heliocentric Model)

Orbits of the planets were still circles.

Determined relative distances between planets and the stars
Closer in the planet to the sun, the ______ it is moving.
Tycho Brahe
No telescope, naked eye observations. Made the best observations that had ever been made of the planets over 20 years.

Observed a supernova.
Johannes Kepler
Copernican Model

Theory must fit the data within the accuracy of the measurements.
Kepler's First Law
The planets move on ellipses with the sun at one focus.
Kepler's Second Law
A line from a planet to the sun sweeps over equal areas in equal intervals of time, thus the planet must be moving at different speeds at different parts of the orbit.
Kepler's Third Law
Period of the orbit squared = length of semi-major axis cubed

"Harmonic Law"

Planets with bigger orbits move slower.
Galileo Galilei
First person to use a telescope to observe the sky.

Moon has mountains and valleys.

Milky Way is made from many faint stars.

Galilean Moons (4) of Jupiter clearly orbit Jupiter, not the Earth.

Sunspots on the sun - not perfect.

Saw that the sun was rotating.

Venus goes through a full set of phases (proved Copernicus right)
Galileo on Physics
Falling objects accelerate.

Law of Inertia
Law of Inertia
An object with a given velocity will maintain that velocity unless acted on by a force
Issac Newton
Calculus, Motion, the Law of Universal Gravity

Linked motion on Earth to motion in the sky.
Newton's First Law
Law of Inertia
Newton's Second Law
Acceleration is a change in a velocity (change in speed or direction)

F = ma
Newton's Third Law
To every action, there is an equal and opposite reaction.
Newton - Law of Universal Gravitation
F = G Mm
r squared
Bound Orbits
Circle, Ellipse

Conic Sections
Unbound Orbits
Parabola, Hyperbola

Conic Sections
Orbits must have:
1.Tangential Velocity
2. Falling

Gravity produces acceleration.

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