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AST301 Hour Exam #1 Terms (Part 2)
N/A
27
Astronomy
Undergraduate 1
02/09/2011

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Term
Altitude(above horizon)
Definition
The angular distance between the horizon and an object in the sky
Term
Angular momentum
Definition
momentum attributable to rotation or revolution. The angular momentum of an object moving in the sky moving in a circle of radius r is the product m*v*r
Term
Astronomical Unit (AU)
Definition
The average distance of the Earth from the Sun, which is about 150 million km
Term
Celestial equator (CE)
Definition
The extension of the Earth's equator on to the celestial sphere
Term
Conservation of energy
Definition
The principle that energy can be neither created nor destroyed, but can only change from one form to another
Term
Conservation of momentum
Definition
The principle that, in the absence of net force, the total momentum of a system remains constant
Term
Eclipse
Definition
Occurs when one astronomical object casts a shadow on another or crosses our line of sight to the other object
Term
Ellipse
Definition
A type of oval that happens to be the shape of bound orbits
Term
Equinox
Definition
either of two times of the year when the sun crosses the plane of the earth's equator and day and night are of equal length
Term
Focus (of ellipse)
Definition
One of two special points within an ellipse that lie along the major axis. When one object orbits a second object, the second object lies at one focus of the orbit
Term
Gravitational potential energy
Definition
Energy that an object has by virtue of its position in a gravitational field; an object has more gravitational potential energy when it has a greater distance than it can potentially fall
Term
Kepler's First Law
Definition
States that the orbit of each planet about the Sun is an ellipse with the Sun at one focus
Term
Kepler's Second Law
Definition
States that, as a planet moves around its orbit, it sweeps out equal areas in equal times. Tells us that a planet moves faster when it is closer to the Sun than when it is farther from the Sun.
Term
Kepler's Third Law
Definition
States that the square of a planet's orbital period is proportional to the cube of its average distance from the Sun, which tells us that more distant planets move more slowly in their orbits
Term
Light-year
Definition
The distance that light can travel in one year, which is 9.46 trillion km
Term
Meridian
Definition
A half-circle extending from your horizon (altitude 0 degrees) due south, through your zenith, to your horizon due north
Term
Newton's First Law of Motion
Definition
In the absence of a net force, an object moves with constant velocity
Term
Newton's Second Law of Motion
Definition
Force=mass*acceleration
Term
Newton's Third Law of Motion
Definition
For any force, there is always an equal and opposite reaction force
Term
Parsec (pc)
Definition
Approximately equal to 3.26 light-years; it is the distance to an object with a parallax angle of 1 arcsecond
Term
Radiative energy
Definition
Energy carried by light; the energy of a photon is Planck's constant times is frequency, or h*f
Term
Revolution (orbit)
Definition
The orbital motion of one object around another
Term
Sidereal month
Definition
About 27.25 days, the time required for the moon to orbit the Earth once
Term
Sidereal period (of a planet)
Definition
A planet's actual orbital period around the Sun
Term
Speed
Definition
The rate at which an object moves. Its units are distance divided by time, such as m/s or km/hr
Term
Tidal force
Definition
The tidal force is a secondary effect of the force of gravity and is responsible for the tides. It arises because the gravitational force exerted on one body by a second body is not constant across its diameter
Term
Velocity
Definition
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
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