constellations
stellar patterns identified by name, usually mythological gods, people, animals or objects; also the region of the sky containing the star pattern
where did the oldest constellation originate?
3000 years ago in assyria
how many ancient constellations are still in use?
48
why did astronomers add 40 more constellations in 1928?
to correct the gap and ambiguities in the constellation boundaries
In todays society what does a constellation represent?
not just a group of stars but an area of the sky and any star within the region belongs to one and only one constellation
asterisms
named groups of stars that are not constellations
what is an example of an asterims
big dipper and is part of the constellation ursa major (the great bear)
what is the great square of pegasus?
an asterisms that includes three stars from pegasus plus alpheratz from andromeda
what is most important to remember about constellations and asterisms?
most are made up of stars that are not physically associated with one another
where do most star names come from?
ancient arabic
how do modern astronomers refer to a star?
by its constellation and a greek letter assigned according to its brightness within the constellation
magnitude scale
how astronomers refer to the brightness of a star
how is the brightest star referred to on a magnitude scale?
first-magnitude, second-magnitude and so on
apparent visual magnitude
the magnitude you see when you look at a star in the sky, which includes only types of light visible to the human eye and does not take into account the stars distance from earth
flux
a measure of light energy related to intensity; the magnitude of a star is related directly to the flux of light received on earth and so to its intensity
north and south celestial poles
pivots on which the sky appears to rotate and they define the four directions around the horizon: the north, south, east and west points
celestial equator
an imaginary line around the sky above earths equator divides the sky into the northern and southern halves
precession
caused by the gravitational forces of the moon and sun acting on the equatorial bulge of the spinning earth and causing its axis to sweep around in a conical motion like the motion of a tops axis
evening stars
planets visible in the sky at sunset
morning stars
planets visible in the dawn sky
milankovitch hypothesis
changes in the shape of earths orbit, in its precession, and in its axial tilt can alter the planets heat balance and cause the cycle of ice ages
evidence found in seafloor samples support this hypothesis
why are most modern constellations composed of faint stars or located in the southern sky?
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how does the greek letter designation of a star give you clues to its location and brightness?
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how did the magnitude system originate in a classification of stars by brightness?
hipparchus complied first known star catalog & ptolemy used magnitude system in his catalog to divide stars into 6 classes; ancient astronomers could only estimate magnitudes
what does the word apparent mean in apparent visual magnitude?
apparent visual magnitude does not take into account the distance to the stars only how bright the star looks as seen from earth
what does the word visual mean in apparent visual magnitude?
only visual light is included; stars that emit light but cannot be seen with the human eye are not included
in what ways in the celestial sphere a scientific method?
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if earth did not rotate, could you define the celestial poles and celestial equator?
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where would you go on earth if you wanted to be able to see both the north and south celestial pole at the same time?
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why does the number of circumpolar constellations depend on the latitude of the observer?
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explain two reasons why winter days are colder than summer days?
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how do the seasons in earths southern hemisphere differ from those in the northern hemisphere?
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why should the eccentricity of earths orbit make winter in earths northern hemisphere different from winter in earths southern hemisphere?
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arc minute
an angular measure one sixtieth of a degree
arc second
an angular measure one sixtieth of an arc minute
celestial pole (north or south)
One of the two points on the celestial sphere directly above Earth's poles.
celestial sphere
an imaginary sphere of very large radius surrounding earth to which the planets, stars, sun and moon seem to be attached
circumpolar constellation
a constellation so close to one of the celestial poles that it never sets or never rises as seen from a particular latitude
east point
one of the four cardinal directions; the point on the horizon directly east
flux
a measure of a flow of energy through a surface; usually applied to light
horizon
the circular boundary between the sky and earth
magnitude scale
the astronomical bightness scale; the larger the number the fainter the star
nadir
the point on the celestial sphere directly below the observer; the opposite of the zenith
north celestial pole
north point
precession
the slow change in the direction of earths axis of rotation; one cycle takes nearly 26,000 years
scientific model
a tentative description of phenomena for use as aid to understanding
south celestial pole
the point on the celestial sphere directly above earths south pole
south point
one of the four cardinal directions; the point on the horizon directly south
west point
one of the four cardinal directions; the point on the horizon directly west
zenith
the point on the sky directly above the observer