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Chapter 2 Astronomy
Terms in this set (52)
The word planet is derived from a Greek term meaning
The planets that were known before the telescope was invented were
Saturn, Venus, Mars, Mercury, and Jupiter.
The motions of the planets against the background stars in our sky can best be described as
regular patterns with general eastward motion interrupted by periods of westward motion.
An apparent eastward motion of a planet from night to night compared to the background stars (as viewed from Earth) is referred to as
When observing planetary motions from Earth, the phrase retrograde motion refers to the
slow westward motion of the planet from night to night compared to the background stars.
The term retrograde motion for a planet refers to the
temporary reversal of the planet's normal west-to-east motion past the background stars as seen from Earth.
Nicolaus Copernicus was the first person to
develop a comprehensive model for a Sun-centered solar system.
The contribution of Copernicus to the development of astronomy was a mathematical model for a
heliocentric cosmology in which the planets move in circular orbits.
Venus experiences all of the following except one. Which is the exception?
Venus can pass in front of the Sun as seen from Earth when it is at
According to the heliocentric theory, which of the following objects can never transit (pass in front of) the Sun as seen from Earth?
When Mercury is at its farthest distance from Earth, it is at
The best time(s) to see inferior planets from Earth is (are) when these planets are at positions of
When Saturn is at its farthest distance from Earth, it is at
When Mars is at opposition, it is
high in the sky at midnight.
When a planet is seen at opposition, it is always at its
closest point to Earth.
The sidereal period of a planet is defined as the time between two successive
passages of the planet in front of a particular point in the sky (e.g., a star) as seen from the Sun.
The synodic period of a planet is defined as the time between two successive
identical configurations (e.g., opposition to opposition).
The greatest inaccuracy in Copernicus' theory of the solar system was
placement of the planets in circular orbits.
The person who compiled the large set of accurate observations of planetary positions that formed the basis for proving that planets move in elliptical orbits around the Sun was
Each planet moves along an elliptical path with the Sun at one focus of the ellipse. What is at the other focus?
A major contribution of Johannes Kepler to the development of modern astronomy was
proof that planetary orbits are ellipses.
Kepler's first law states that a planet moves around the Sun in a(n)
elliptical orbit, with the Sun at one focus.
The eccentricity of a planet's orbit describes
its shape compared to that of a circle.
A perfect circle is an ellipse with an eccentricity of
The distance from the perihelion point to the aphelion point of a planetary orbit is
the major axis.
In an ellipse, the major axis is a distance measured
along the longer diameter, passing through the foci of the ellipse.
The semimajor axis of an ellipse is
the distance from the center of the ellipse to one end, along the largest diameter of the ellipse.
To which point in a planetary orbit does the word perihelion refer?
point closest to the Sun
To which point in a planetary orbit does the word aphelion refer?
point farthest from the Sun
Kepler's third law tells us that the
square of a planet's period in years is the same number as the cube of its semimajor axis in AU.
If a tenth planet (tentatively predicted to exist on the basis of perturbations in the orbits of Uranus and Neptune) were to be discovered with a sidereal period of 200 years, what would be the radius of its orbit (assumed to be circular)?
One light-year is a distance of approximately
9.5 × 1012 km.
A light-year is a measure of
1 AU, or 1 astronomical unit, is defined as the
mean distance between the Sun and Earth.
An astronomical unit (AU) is a unit of
length, the average distance between the Sun and Earth.
To specify an object's velocity completely, we need to specify its
speed and direction of travel.
A body whose velocity is constant
has zero acceleration
The acceleration of an object is defined as the rate of change of its
Newton stated that if a force were applied to an object in space, the resultant acceleration would depend on the
mass of the object.
The mass of an object is a measure of how
difficult it is to accelerate.
If a planet were to exist in our solar system in a circular orbit with a radius of 3 AU, about how long would it take to orbit the Sun once?
What is the distance between Earth and the nearest star?
The semimajor axis of Earth's orbit is
What path would a planet (like Earth!) take if the force of gravity from the Sun were to be suddenly removed?
The planet would move in a straight line tangential to its present orbit.
The careful description of the velocity of a moving object at a particular time requires that one define the
speed and direction of the moving object.
Which of the following four objects or persons is not accelerating?
Olympic swimmer exerting considerable force to maintain a constant speed in a straight line through the water
According to Newton's laws, a force must be acting whenever
the direction of an object's motion changes.
An accelerating body must at all times
have a changing velocity
Which of the following statements is a correct version of Newton's third law?
Whenever some object A exerts a force on some other object B, B must exert a force of equal magnitude on A in the opposite direction.
According to Newton's third law, if a force is acting on an object, then
there must be some other force acting on a different object, with the same magnitude but in the opposite direction.
What is the size of the force you exert on Earth compared to the force Earth exerts on you as you stand on its surface?
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