Space Chapter 7
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what is a celestial object?
any object that exists in space, such as a planet, a star, or the Moon
what is an astronomer?
- a scientist who studies astronomy, which is the study of the night sky
- first astronomers were the mesopotamians, who made calendars
what is a revolution?
- the time it takes for an object to orbit another object; earth's revolution around the sun is 365.24 days (reason for leap years)
what is a rotation?
- the turning of an object around an imaginary axis running through it
- (one day is one rotation-24 hours)
what is a constellation?
- a group of stars that seem to form a distinctive pattern in the sky (eg. big dipper, ursa major)
what is a light year?
- the DISTANCE light travels in one year
- about 9.5x 1012km
- DOES NOT MEASURE TIME
What is apparent magnitude?
- the brightness of a star as seen from earth
- (sun looks brightest because it is closest but there are many brighter ones in existance)
what is an asterism?
- a smaller group of stars that form patterns within a constellation
- (big dipper within ursa major)
what are pointer stars?
- the big dippers two end stars are called pointer stars because they poin towards polaris, the north star. five times the distance between these stars in the direction they point should lead to polaris.
what are tides?
- the rising and falling of ocean waters as a result of the Moon's gravity and the Earth's gravity
what are phases of the moon?
- the monthly progression of changes in the appearance of the Moon, which result from different portions of the Moon's sunlit side being visible from earth
what is a lunar eclipse?
- the phenomenon in which the full moon passes into earths shadow
what is a solar eclipse?
the phenomenon in which the shadow of the moon falls on earths surface
why do we have seasons?
earth rotates at a tilt of 23.5o
during the summer in the northern hemisphere, when earth is tiltled toward
the sun, it receives more solar radioation at a highter angle for longer periods of time. in winter, the northern hemisphere is tilted away
from the sun. the opposite happens in the southern hemisphere.
what is a planet?
- an object that orbits one or more stars (and is not a star itself), is spherical, and does not share its orbit with another object
- the inner planets are mercury, venus, earth, and mars. sometimes they are called terrestrial planets, relativley small, and have solid cores.
- large clumps of gas,ice and dust compose the outer planets or gas giants, which are jupiter, saturn, uranus, and neptune, they are known for their gaseous bands and cold temperateures.
what is the solar system?
- a group of planets that circle one or more stars
what is retrograde motion?
- the movement of an object in the sky, usually a planet, from east to west, rather than in its normal motion from west to east
what is an orbital radius?
the average distance between the Sun and an object that is orbiting the sun
what is an astronomical unit?
- the average distance between earth and the sun, about 1.5x108 km
what is a comet?
an object composed of rocky material, ice and gas; comes from the Kuiper belt and Oort cloud
what is a meteroroid?
a peice of rock moving through space
what is a meteor?
a meteoroid that hits Earths atmosphere and burns up
what is a meteorite?
a meteoroid that is large enough to pass through earths atmospehere an reach the ground, without being totally burned up
what are trans-neptunian objects?
- objects that circle the sun beyond the orbit of Neptune
- located it the Kuiper Belt (disc shaped group of small objects orbiting the sun)
- predicted to be there when the solar system formed
what is an asteroid?
an object in space that ranges in size from a tiny speck, like a grain of sand, to 500km wide, most asteroids originate in the asteroid belt between Mars and Jupiter
what is a geocentric model?
a model of the solar system stating that the earth is the center of all planetary motion, with the planets and the sun travelling in perfect circles around the earth
what is a heliocentric model?
a model of the solar system in which the sun is in the centre with the planets orbiting it
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