Download Astronomy Concepts: Seasons, Eclipses, Tides, Kepler's Laws, and Newton's Laws and more Quizzes Astronomy in PDF only on Docsity!
What causes seasons?
The Earth's tilt causes seasons. TERM 2
When do we have summer in the northern
hemisphere?
DEFINITION 2 We have summer in the northern hemisphere when the northern hemisphere is tilted toward the Sun. TERM 3
Why is it warmer in the summer than in the
winter?
DEFINITION 3 It is warmer in the summer than in the winter because the sunlight is more concentrated on the ground when the Sun is higher in the sky. TERM 4
When do the vernal and autumnal equinoxes
occur?
DEFINITION 4 When the declination of the Sun is zero degrees, or located on the celestial equator. TERM 5
What is the vernal
equinox?
DEFINITION 5 The first day of spring.
What is the autumnal
equinox?
The first day of fall. TERM 7
When do solar eclipses occur?
DEFINITION 7 Solar eclipses occur when the Moon is between the Sun and the Earth. They occur at NEW MOON. TERM 8
When do lunar eclipses occur?
DEFINITION 8 Lunar eclipses occur when Earth is between Sun and Moon. Lunar eclipses occur at FULL MOON. TERM 9
What causes tides?
DEFINITION 9 Tides are caused by the difference between the Moon's gravitational force on different sides of the Earth. TERM 10
What is the time between high tides?
DEFINITION 10 12 hours, 25 minutes
What is tidal breaking?
Tidal breaking occurs when friction robs energy from Earth's rotation and uses it to heat the ocean. This occurs because tidal forces are slowing Earth's rotation and enlarging the Moon's orbit. The ocean's tidal bulges press down on the ocean floor, causing the friction. TERM 17
Retrograde
DEFINITION 17 Motion that is backward compared to the norm. For example, we see Mars in apparent retrograde motion during the periods of time when it moves westward, rather than the more common eastward, relative to the stars. TERM 18
Epicycle
DEFINITION 18 The small circle on which a planet moves while simultaneously going around a larger circle (the deferent) around Earth in the (Earth-centered) Ptolemaic model of the universe. TERM 19
What is the geocentric model?
DEFINITION 19 This is by Ptolemy. He said that the planet moves in a small circle called the epicycle. The center of the epicycle moves in a large circle called the deferent. The combination of small and large circles produces a loop the loop motion. TERM 20
What is the heliocentric model?
DEFINITION 20 This is by Copernicus. He said that the Sun, not the Earth, is at the center of the universe. He said that the Earth revolves around the Sun and that it rotates around its axis.
When do retrograde motions occur naturally?
Retrograde motions occur naturally if planets further from the Sun move more slowly. For example, Earth and Mars. Earth's orbital radius is 1 AU and its orbital speed is 30 km/sec. Mars' orbital radius is 1.5 AU and its orbital speed is 24 km/sec. As Earth "laps" Mars, Mars appears to go backward as seen by an observer on Earth. This is the apparent retrograde motion. TERM 22
Why is Copernicus' model met with great
resistance?
DEFINITION 22 It implies that the distance from the Sun to the stars is much greater than the distance from the Sun to the Earth. TERM 23
What are the radical aspects of the
Copernican model?
DEFINITION 23
- Earth is not at the center of the universe.2) Earth is moving.3) Earth is just another planet.4) Space is big-- really big. TERM 24
What are the conservative aspects of the
Copernican model?
DEFINITION 24
- Uniform circular motion assumed2) Epicycles are still required TERM 25
Eclipse
DEFINITION 25 An event in which one astronomical object causes a shadow on another or crosses our line of sight to the other object.
What is Kepler's first law of planetary
motion?
Each planet moves in an ellipse with the Sun at one focus. TERM 32
What happens to the ellipse when the foci are
close together?
DEFINITION 32 The ellipse is nearly circular and the eccentricity is close to zero. TERM 33
What happens to the ellipse when the foci are
far apart?
DEFINITION 33 The ellipse is very flattened and the eccentricity is close to one. TERM 34
What is Kepler's second law of planetary
motion?
DEFINITION 34 The line between the Sun and the planet sweeps over equal areas in equal time intervals. TERM 35
What are the consequences of Kepler's
second law?
DEFINITION 35 Planets move fastest when closest to the Sun.
What is Kepler's third law of planetary
motion?
The ratio of the cube of the semi-major axis to the square of the period is the same for each planet. The square of a planet's orbital period is proportional to the cube of its average distance from the Sun: P^2 = a^3.This law means no more epicycles. TERM 37
What did Galileo say in "The Starry
Messenger" or "Sidereus Nuncius"?
DEFINITION 37
- Mountains on the Moon: Aristotle and Ptolemy said the Moon is a perfect, smooth sphere. But the Moon is no more perfect than the Earth.2) The Sun has spots on its surface. The Sun is not perfect. Motion of sunspots indicates that the Sun is rotating.3) The planet Jupiter has moons of its own. Four "Galilean moons of Jupiter: Io, Europa, Ganymede, and Callisto. The Earth is NOT the center of all orbits in the universe.4) Venus shows phases like those of the moon. Venus goes through all phases: looks big when nearly new, looks small when full. TERM 38
Velocity
DEFINITION 38 The combination of speed and direction of motion; it can be stated as a speed in a particular direction, such as 100 km/hr due north. (speed plus direction of travel, ex. 65 miles/hour to the north) TERM 39
Speed
DEFINITION 39 Rate at which an object changes its position. Ex: 65 miles/hour TERM 40
Acceleration
DEFINITION 40 The rate at which an object's velocity changes. Its standard units are m/s^2. It can involve 1) increase in speed, 2) decrease in speed, or 3) change in direction.
What is Newton's First Law of Motion?
An object remains at rest, or moves in a straight line at constant speed, unless acted on by an outside force. What is TERM 47
What is Newton's Second Law of Motion?
DEFINITION 47 The acceleration of an object is directly proportional to the force acting on it, and inversely proportional to its mass. In mathematical form: a = F/m or F = ma. Or alternatively, F = G(Mm/r^2) TERM 48
What is Newton's Third Law of Motion?
DEFINITION 48 For every action, there is an equal and opposite reaction. Whenever A exerts a force on B, B exerts a force on A that's equal in size and opposite in direction. All forces come in pairs. TERM 49
What is Newton's Law of Gravity?
DEFINITION 49 Gravity is an attractive force acting between all pairs of massive objects. Gravity depends on 1) masses of the two objects, and 2) distances between the objects. TERM 50
Gravitational force varies _____ with mass and
_____ with square of distance.
DEFINITION 50 directly; inversely
What was Newton's assumption about the
Moon's orbit?
He said that the Moon is on a circular orbit. Even if its orbit were perfectly circular, the Moon would still be accelerated. TERM 52
How did Newton expand Kepler's first law of
motion?
DEFINITION 52 While Kepler said that the orbits of the planets around the Sun are ellipses with the Sun at one focus, Newton said that the orbits of ANY PAIR OF OBJECTS are CONIC SECTIONS with the CENTER OF MASS at one focus. TERM 53
Light-year
DEFINITION 53 (ly) The distance that light can travel in one year. 1 light year = 9.5 x 10^12 km. It's a unit of distance. TERM 54
Energy of a photon
DEFINITION 54 The energy of a photon is related to the frequency of a wave. E = hf. E= energy of a photonf = frequency of lighth = Planck's constanth = 6.626 x 10^-34 joule x s TERM 55
What does a longer wavelength mean?
DEFINITION 55 A lower frequency
What causes an absorption in the
spectrum?
To excite an electron into a higher energy orbit, you need to absorb exactly the energy difference between orbits (absorb a photon of exactly that energy or collide with an atom or electron and get the energy from the motion of the collider). TERM 62
What causes an emission on the spectrum?
DEFINITION 62 To de-excite, an electron must rid itself of exactly the amount of excess energy (emit a photon of the exact energy or give up the energy to a colliding atom or electron; no photons are emitted). TERM 63
What do spectral lines tell us?
DEFINITION 63 Atoms and molecules can only emit or absorb photons at particular wavelengths. In emission lines, photons are emitted at particular wavelengths when an electron jumps from a higher to a lower energy orbit. In absorption lines, photons are absorbed at particular wavelengths if their energy is exactly enough to make an electron jump up to a higher energy orbit.From TERM 64
What do we know from emission and
absorption lines?
DEFINITION 64
- which elements are present2) whether they are ionized3) whether they are in molecules TERM 65
Blackbody
DEFINITION 65 An object that absorbs all light. It absorbs at all wavelengths and is characterized by its temperature. It is also the perfect radiator. It emits at all wavelengths (continuous spectrum). The total energy emitted depends on temperature. The peak wavelengths also depends on temperature.
Temperature
A measure of the average speed of the atoms. An object is hot when the atoms of which it is made are in rapid random motion. Random motions stop at absolute zero temperature. TERM 67
What produces a continuous spectrum?
(Kirchoff's laws)
DEFINITION 67 A hot solid or a hot, dense gas TERM 68
What produces an emission-line spectrum?
(Kirchoff's laws)
DEFINITION 68 A hot, low density gas. Light is emitted only at wavelengths corresponding to energy differences between permitted electron orbits. TERM 69
What produces an absorption-line spectrum?
(Kirchoff's laws)
DEFINITION 69 A continuous spectrum source viewed through a cool, low- density gas.Consider a cold, low density cloud of hydrogen in front of a hot blackbody. Light is absorbed only at wavelengths corresponding to energy differences between permitted electron orbits. TERM 70
How does temperature of a star relate to its
color?
DEFINITION 70 Reddish stars are cooler while bluish stars are hotter.
