Astrology Exam 1
What do light years measure?
distances in light-years correspond directly to light-travel times. For example, light takes 100 million years to reach us from a galaxy that is 100 million light-years away. This fact helps astronomers to reconstruct the history of the universe.
What is the celestial equator
projection of Earth's equator into space
In winter, Earth's axis points toward the star Polaris. In spring
the axis also points toward Polaris.
what is the major axis?
the line that passes through the star and connects the nearest and farthest points of the planet's orbit is called the major axis, and half this line is the semimajor axis — which we consider the planet's average distance from the star.
Two stars that are in the same constellation
may actually be very far away from each other.
what would a greater axis tilt do to the Earth's seasons?
more extreme temperature differences
How many arcminutes are in a full circle?
2.16×10^4 arcminutes
An astronomer looks at the Andromeda galaxy (the other large galaxy in the Local Group) through her telescope. How long ago did that light leave Andromeda?
2.5 million years
What is parallax?
The apparent shift in position of an object caused by a change in the observer's position. The farther away an object the smaller the parallax
Which of the following statements best describes what astronomers mean when they say that the universe is expanding?
The average distance between galaxies is increasing with time.
What is the ecliptic plane?
The ecliptic plane is defined as the imaginary plane containing the Earth's orbit around the sun. In the course of a year, the sun's apparent path through the sky lies in this plane. Tilted 23.5 Degrees
In the Greek geocentric model, the retrograde motion of a planet occurs when
The planet actually goes backward in its orbit around Earth.
What is eccentricity?
The shape of Earth's orbit. Eccentricity is a measure of how "stretched out" an ellipse is. A perfect circle has zero eccentricity, and the most stretched out ellipse has the largest eccentricity.
According to current scientific estimates, when did the Big Bang occur?
about 14 billion years ago
When do we have a solar eclipse?
at new moons near a node
When do we have a lunar eclipse?
When the moon is full and close to a Node
Why do the planets orbit the Sun (i.e. why don't they crash into the Sun)?
Although the planets experience a force of gravity from the Sun, since they are moving, their trajectories bend around the Sun rather than lead directly into the Sun.
Why do we essentially see the same face of the Moon at all times?
Because the Moon's rotational and orbital periods are equal.
What two factors affect a planets temperature?
Distance from the Sun and directness of sunlight
What is really happening in space during the periods when we see Mars going through apparent retrograde motion?
Earth is passing by Mars in its orbit around the Sun.
because Earth rotates West to East, the stars appear to move...
East to West
If an astronomer claims to have discovered an object with a very eccentric orbit, which of the following best describes the orbital trajectory of the object?
It looks like a very squashed oval.
What is Kepler's first law?
Kepler's first law states that the orbit of each planet is an ellipse with the Sun at one focus
What is Kepler's second law?
Kepler's second law states that as a planet orbits the Sun, it sweeps out equal areas in equal times. Kepler's second law tells us that a planet moves faster in its orbit when it is closer to the Sun (near perihelion) than when it is farther (near aphelion). This law applies to all planets and therefore explains the statement about Mars.
What is Kepler's third law?
Kepler's third law states that a planet's orbital period, p, is related to its average (semimajor axis) orbital distance, a, according to the mathematical relationship p2=a3.
What are the phases of the moon?
New Moon, Waxing Crescent, First Quarter, Waxing Gibbous, Full, Waning Gibbous, Third Quarter, Waning Crescent, Dark Moon.
Where are the North and South Celestial Poles located
North and south Pole
Why doesn't a total lunar eclipse occur every month?
Sometimes the Moon is above or below Earth's shadow during a full moon.
What causes the seasons?
The tilt of the Earth's axis; changing the amount of direct sunlight.
Roughly what time of day is a Third Quarter Moon highest in the sky?
dawn
In Ptolemy's Earth-centered model for the solar system, Venus's phase is never full as viewed from Earth because it always lies between Earth and the Sun. In reality, as Galileo first recognized, Venus is __________.
full whenever it is on the opposite side of the Sun from Earth
If Earth's orbit were very eccentric, but the average distance from the Sun were still 1 AU, its orbital period
would still be one year.