Midterm Study 1 Flashcards
To be a planet:
Stability to be round and circular, orbits a star, the planet should clear the path of its orbit
Earth’s Local Address
Earth -> Solar System -> Solar System Neighborhood -> Orion Arm -> Milky Way Galaxy -> Satellite Galaxies -> Local Galactic Group -> Virgo Supercluster [Local Galactic Group and Virgo Cluster are both part of the Virgo Supercluster] -> Laniakea Massive Supercluster -> Observable Universe
Speed of light is:
3 * 10^8 meters/second
Constellations
a group of stars seen as forming a figure or design in the sky
North Celestial Pole
the point in the sky where the Earth’s axis of rotation extends to intersect the celestial sphere
South Celestial Pole
The point in the sky where Earth’s axis of rotation intersects the celestial sphere, directly above Earth’s South Pole
The Ecliptic
the Sun’s path in our sky projected on the Celestial Sphere
Celestial Equator
the projection into space of the earth’s equator; an imaginary circle equidistant from the celestial poles.
Celestial Sphere
an imaginary sphere of which the observer is the center and on which all celestial objects are considered to lie.
Earth rotates which direction?
counterclockwise
Declination
is the distance of an object North or South of the celestial equator (horizontal lines; measured in degree increments of 15)
Right Ascension
is the angular distance eastward along the celestial equator from the vernal equinox (measured in hours; East along the equator)
Vernal Equinox
is the point on the equator where the ecliptic (path of the Sun) goes from South to North (i.e, crosses the celestial equator); where RA=0, Dec=0
Altitude
the angle from the horizon to the object
Azimuth
the angle from the North measured East along the horizon to the object
Advantages/Disadvantages of the Horizontal Coordinate System
Advantage: Very simple
Disadvantage: Specific to every individual location on Earth
Advantages/Disadvantages of the Equatorial Coordinate System
Advantage: Unified and definitive
Disadvantage: Relatively complex
Geocentric Model
a theory of the universe that places the Earth at the center, with the Sun, Moon, stars, and planets orbiting it
Heliocentric Model
a cosmological model that places the sun at the center of the solar system, with the planets revolving around it
Tychonic Geo-Heliocentric Model
the Earth is at the center of the universe, the Sun and Moon and the stars revolve around the Earth, and the other five planets revolve around the Sun
Retrograde Motion
planets appear to move backwards through the sky. Caused by relative position between earth and planet relative to background stars
Prograde Motion
ordinary planetary motion (Eastward, from West to East night by night. Remember, every night things still rise in the East and set in the West)
Inferior Planets
Planets inside Earth’s orbit
Superior Planets
Planets outside Earth’s orbit
Superior Conjunction
occurs when a planet, asteroid, or comet is on the opposite side of the sun from Earth, and all three bodies are nearly in a straight line; forms right angles at greatest elongation; the planet is on the other side of the Sun from Earth
Sidereal Period
the time it takes for a celestial body to complete one orbit around the sun in relation to the fixed stars
Synodic Period
the time it takes for a celestial body to return to the same position relative to the Sun as seen from Earth; the time it takes for the same Sun-Earth-Planet configuration to be reached again, eg from opposition to opposition. (Synodic period - the planet nods at you on the way past).
Philolaus and Hicetas (470-385 BC)
Geocentric universe
Eudoxus (380 BC)
Geocentric universe
Aristarchus of Samos (310 BC)
Heliocentric universe
Ptolemy (90–168 CE)
Geo-epicyclic universe. The motions of the Sun, our Moon, and the planets have been studied. His method of epicycles described the paths of the planets
Nicolaus Copernicus (1473–1543)
Foundation and backing of heliocentric universe
Tycho Brahe (1546–1601), Johannes Kepler (1571–1630) and Galileo Galilei (1564-1642)
Motion of planets. Geo-heliocentric universe, Kepler’s law of motion, use of telescope in astronomy
Isaac Newton (1642 – 1726)
Connected the acceleration of objects near Earth’s surface with the centripetal acceleration of the Moon in its orbit about Earth
Albert Einstein (1879 – 1955)
Theory of General Relativity (Gravity)
Kepler’s First Law:
The Law of Ellipses: Each planet’s orbit about the Sun is an ellipse
Kepler’s Second Law
The Law of Equal Areas: A planet covers the same area of space in the same amount of time no matter where it is in its orbit; empirical law, equal areas explains that the planet moves fastest when it is closest to the Sun and slowest furthest from the Sun
Kepler’s Third Law
The Law of Harmonies: A planet’s orbital period is proportional to the size of its orbit (its semi-major axis); the square of the planet’s sidereal period is proportional to the cube of the semi-major axis of its orbit;
P^2 ∝ a^3
Perihelion
the point in the orbit of a planet or other astronomical body, at which it is closest to the sun
Aphelion
the point at which an orbiting body is furthest from the sun
What causes Earth’s seasons?
Its tilt, NOT its orbit. Light, and thus heat, from the Sun is dispersed unevenly across Earth’s surface due to its tilt, causing it to take longer to heat up during the Winter where the Sun’s movement is closer to the horizon and thus has shorter days, and causing it to heat up quicker during the Summer when the Sun’s movement is “higher up” in the sky and thus more successfully capable of heating the surface (direct sunlight/heat)
Earth’s Tilt is:
About 23.5°
Three Movements of Earth:
Rotation, Revolution, Axis (Precession); Earth rotates counterclockwise every 23 hours, 56 minutes, and 4 seconds, it revolves around the Sun every about 365 days, and is tilted on its axis by 23.5°, causing precession
Precession
the gradual change in the orientation of a celestial body’s rotational axis or orbital path. It’s similar to a planet’s “wobble,” like a spinning top that wobbles while it rotates
Eccentricity (e)
a measure of how elliptical an ellipse is;
e = 0 (perfectly circular), e > 1 (hyperbolic and will exit system), e = 1 (linear or parabolic)
Occam’s Razer
the problem-solving principle that recommends searching for explanations constructed with the smallest possible set of elements
Conjunction
the planet is on the other side of the Sun from Earth. It will rise and set with the Sun. At exact Conjunction, the planet is behind the Sun and impossible to see
Opposition
the planet is on the opposite side of Earth from the Sun. It will be brightest in the sky. Opposition is where it exhibits retrograde motion.
Quadrature
when a planet as seen from Earth creates a right angle with the direction of the Sun
Inferior Conjunction
the planet is on this side of Earth from the Sun
Greatest Elongation
the farthest a planet gets from the Sun in the sky
Semi-Major Axis
One half of the major axis of the elliptical orbit; also the mean distance from the Sun
Orbital Period
Essentially another name for Sidereal Orbit
Force
an interaction that causes change in the motion of an object
Acceleration
change in speed or change in direction
Scaler Quantities
quantities that does not require direction [ex: weight]
Vector Quantities
quantities that do require direction [ex: displacement]
Newton’s First Law
Law of Inertia: Objects at rest stay at rest, objects in motion stay in motion (unless acted upon by an outside force)
Newton’s Second Law
- Unbalanced Forces Cause Motion: Motion, change in velocity; these are caused by unbalanced forces (F = ma): The acceleration of an object depends on the mass of the object and the amount of force applied
Newton’s Third Law
Equal and Opposite: If something is pushed back, it pushes back with an equal force: Whenever one object exerts a force on another object, the second object exerts an equal and opposite on the first
Velocity
speed in a given direction
Acceleration
change in velocity: ∆v/∆t
Speed
distance covered in a period of time: s = d/t
Momentum
the quality of motion, such as, mass in motion: the product of the mass and velocity of an object: p = mv
p = kilograms/meters/per-second
Inertia
an object’s resistance to change in motion: I = L/w
Scientific Law
describes what happens
Scientific Theory
describes why or how it happens
Weak Nuclear Force
the mechanism of interaction between subatomic particles that is responsible for the radioactive decay of atoms
Strong Nuclear Force
keeps the nucleus of atoms together: the force binds protons and neutrons together to form a nucleus and is called the nuclear force
Electromagnetism
an interaction that occurs between particles with electric charge via electromagnetic fields
Gravitation
the attractive force between two objects: the universal force of attraction acting between all matter. It is by far the weakest force known in nature:
* The attractive force between two objects that have mass
The gravity on Earth is about 9.8〖m/s〗^2
Mass
a measure of the amount of material in an object
* [Kilograms or similar are Units of Mass]
Weight
the gravitational force acting on an object attracted by a planet: w = mg
* [Newton is the Unit of Weight]
Gravity Causes Acceleration
Since a = F/m , and a is constant, the force depends on the mass
We can rewrite Newton’s second law (F = ma) for objects on the surface of Earth as:
F(weight) = mg
Where g is the acceleration due to gravity (local).
Universal Law of Gravitation
Gravity is a force between any two objects having mass. The force due to gravity has the following properties:
It is an attractive force acting along a straight line between the two objects It is proportional to the product of the masses of the objects (m_1×m_2) It is inversely proportional to the square of the distance r between the centers of the two objects
Center of Mass
the point at which the whole mass may be considered as concentrated
Tidal Forces
the result of gravitational differences between two objects;
* A phenomenon which deforms the shapes of the planet, tear celestial bodies apart
* Reason of formation of ring system around the planets
* Creates the tides of Earth’s oceans
Why do tidal forces cause bulging?
Why does it bulge on both sides? Earth is rotating; its centripetal force pushes out as one side is pulled all while Earth is spinning; the opposing force of inertia clashing with the pull of the moon.
Tidal Forces Moon
The Moon pulls most on the closest object, and thus the force of the Moon’s pull is distributed differently across Earth, resulting in a drag opposite of the main pull of the Moon, where:
F_tidal=(2GM_E M_E R_E)/(d_(Earth-Moon)^3)
Spring Tides
a phenomenon that occurs when the Earth, Moon, and Sun are aligned, causing the oceans to bulge more than usual
Tidal Locking
a phenomenon in astronomy that occurs when an object’s rotation matches its orbit, causing one side of the object to always face the body it orbits
Neap Tides
a period of moderate tides when the sun and moon are at right angles to each other;
weakest tides
Earth and the Moon: Tidally Locked
The Earth’s gravity slows down the Moon’s rotation, causing the Earth and the Moon to be tidally locked. This means that the Moon’s rotation rate no longer changes over the course of its orbit around Earth. The Moon does not rotate through its bulge and is permanently deformed.
Tides Affect on Earth and Moon
Due to the tides, neither Earth nor the Moon are perfectly spherical. Earth’s leading edge causes acceleration of the Moon, resulting in the Moon’s orbit increasing 3.83 centimeters every year. The Moon’s orbital period increases by about 0.014 seconds every 100 years.
Solar Day
time taken for Earth to rotate the Sun and return to the same place in the sky [24 hours]; we spin more than 360° to get the Sun back to the same place in the sky; the time it takes for Earth to rotate for the Sun to be back in the same place
Sidereal Day
time taken for the Earth to spin 360° 23h 56m 4s once relative to the background of the stars
Lunar Day
time taken for Earth to rotate to get the Moon back in the same place in the sky; 24h 50m
Tides Summary
- Two high tides per lunar day and two low tides per lunar day
- Tidal forces stretch objects
- Tidal forces induce a symmetrical response even though the object creating the tidal force is only present on one side of the other
- Tidal forces mean that the object is squashed slightly
- Total tidal force = actual force – average force
- Tidal forces cause de-acceleration of the objects in question
- The Moon is tidally locked with Earth because of the slow down over time
- Scientists think early, powerful tides helped develop complex life on Earth
Orbit
the regular, repeating path that one object in space takes around another object or center of gravity
Orbits
An orbit is essentially one body falling around another. For example, ignoring air resistance, if you drop a cannonball, it will fall straight down to Earth. However, if you fire a cannonball out of a cannon, it follows a curved path before it lands (it follows the curvature of the Earth).
Theoretically, if there were no other outside forces, firing a cannonball would result it the object constantly falling following the curvature of the Earth, thus creating an orbit.
Orbital Velocity
velocity sufficient to cause a natural or artificial satellite to remain in orbit:
V_c ≈ √(GM/R)
Escape Velocity
the lowest velocity which a body must have in order to escape the gravitational attraction of a particular planet or other object:
V_e ≈ √(2GM/R)
