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41 Cards in this Set

  • Front
  • Back
The Universe
is the totality of all space, time, matter, and energy
Is the study of the universe.
What is a light year
A widely used unit of distance in atronomy. It's the distance a beam of light travels in 1 year.
the scientific method
is a methodical approach emploed by scientists to explore the universe around us in an objective manner
A theory
is a framework of ideas and assumptions used to explain some set of obersvations and make perduictions about the real world.
Early observers grouped Stars visable to the naked eye into patters called constllations.

The patterns have no physical significance, it's just a useful way of labeling regions of the sky.
Earth's rotion
the nightly motion of the stars across the sky is a tesult of the earth's rotation on its axis.
Celestial Sphere
Astronomers imagined that the stars were atached to a vast celestial sphere centerd on Earth and that the motion of the heaves were caused by the roation of the celistal sphere about a fixed earth.
Celestial Sphere
The point where the earth's The axis of rotation intersects the celestial sphere are called the north and south celestial poles.
Celestial Equator
The line where earth's equatorial plane cuts the celestial sphere.
Solor Day
The time from one noon to the next.
Sideral day.
The time between successive risings of any given star is one sideral day.
What Day is Longer. The Solor or Sideral Day?
because the earth revovles around the sun, the solar day is a few minutes longer than the sidereal day.
What is an Ecliptic
The Sun's yearly path around the celestial sphere, or equivalently, the plane of Earth's orbit around the sun, is called the ecliptic.
What is the Zodiac
The constellations lying along the ecliptic are collectively called the zodiac.
Why do we have seasons?
Because Earth's axis is inclinded to the plane of the ecliptic, we experience different seasons depending on which hemisphere (happens to be "tipped" toward the Sun.
What is the summer Solstice?
At the summer solstice the Sun is highest in the sky, and the lenght of the day is greatest.
What is the Winter solstice?
At the winter solstice, the sun is lowest, and the day is shortest.
What is the veral and Autumnal equinoxes?
The earth's axis of rotation is perpendiclar to the line joining Earth to the Sun, so day and night are of equal lenght.
What is a tropical year?
the interval of time from one vernal equinox to the next is one tropical year.
What is the mean solar day?
The speed in which the sun traverses the ecliptic varies around the year, so the noon-to-noon solar day is not consant. The mean solar day is the average solar day over the entire year.
When does noon occure?
Noon occurs when the sun crosses the local meridian.
How did we standardize time?
We divided the earth into 24 standard time zones. and within each zone, all clocks, keep the same standard time.
What is universal time?
Standard time in the time zone of 0 Degrees longitude is universal time.
Why do we have a leap year and how is the leap year calculated?
One tropical year is not a whole number of mean solar days. In order to keep the average lenght of calendar year equal to 1 tropical year, an extra day is inserted into the calendar on leap years.
How do we see the glow of the moon?
The moon emits no light of its own but shines by reflected sunlight.
What are lunar phases?
the light we see reflected off the sun as the moon orbits the earth.
What is the synodic month?
the time betweeen successive full moons?
What is one sidereal month?
The ammount of time taken for the moon to return to the same position in the sky, relative to the stars.

note: Because of earth's motion around the sun, the synodc month is about 2 days longer then the sideral month.
What is a sidereal year?
the time required for the earth complete one orbit around the sun, relative to the sars.
What is precession motion?
it is the slow "wobble" of Earth's axis due to the influence of the Moon. As a result, the sidereal year is slightly longer than the tropical year.
What is a Lunar Eclipse?
When the moon enters the earths's shadaw a lunar eclipse occurs.

It can be total or partial eclipse.
What is a solar eclipse?
When the moon pases between earth and the sun so that a small part of the earth's surface is plunged into shadow.
What is the umbra?
A total solar eclipse is an umbra.
What is the penumbra?
A partial solar eclipse is the penumbra.
What is an annular eclipse?
It occurs when the moon happens to be too far from the Earth for its disk to completely hide the sun.
What is the eclipse seaons?
Because the Moon's orbit around the earth is slightly inclined with respect to the scliptic, solar and lunar eclipses do not occur every month, but only during eclipse season. (twice per year)
What is trianglaution?
Trianglation determines the distances to faraway objects.
What is the cosmic distance scale?
is the family of distance measurement techiques by which astromomers chart the universe.
What is the parallax?
The parallax is the apparent motion of a foreground object relative to a distant background as the obeserver's postion changes.
What is the baseline?
the larger distance between two observation points, the greater is the paralax.