ASTA01 CHEAT SHEET.docx

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Field view: the area visible in an image, usually given as the diameter of the region Solar system: the Sun and its planets, asteroids, comets and so on Scientific notation: the system
of recording very large or very small numbers by using the powers of 10 Supercluster: a cluster of galaxy clusters Planet: a non-luminous body in orbit around a star, large enough to
be spherical and to have cleared its orbital zone of other objects Star: a globe of gas held together by its own gravity and supported by internal pressure, which generates energy by
nuclear fusion AU: Average distance from Earth to the Sun; 1.5 x 108 km Galaxy: a large system of stars, star clusters, gas, dust, and nebulae orbiting a common center of mass
Milky Way: the hazy band of light that circles our sky, produced by the glow of our galaxy Spiral arms: long spiral pattern of bright stars, star clusters, gas, and dust. Spiral arms
extend from the center to the edge of the disk of spiral galaxies Constellation: one of the stellar patterns identified by name, usually of mythological gods, people, animals, or objects.
Also, the region of the sky containing that star pattern Asterism: a named grouping of stars that is not one of the recognized constellations Magnitude scale: the astronomical
brightness scale. The larger the number, the fainter the star Apparent visual magnitude (Mv): a measure of the brightness of a star as seen by human eyes on Earth flux: a measure of
the flow of energy out of a surface. Usually applied to light. Celestial sphere: an imaginary sphere of very large radius surrounding Earth to which the planets, stars, sun, and moon
seem to be attached Scientific model: a concept that helps you think about some aspect of nature without necessarily being true Precession: the slow change in orientation of the
Earth’s axis of rotation. One cycle takes nearly 26000 years Horizon: the circular boundary between the sky and Earth Zenith: the point in the sky directly above the observer Nadir:
the point on the celestial sphere directly below the observer; the opposite of the zenith North and South Celestial Poles: the points on the celestial sphere directly above Earth’s north
and south poles Celestial equator: the imaginary line around the sky directly above Earth’s equator North, south, east and west points: the four cardinal directions; the points on the
horizon in those exact directions Angular distance: the angle formed by lines extending from the observer to two locations in the sky Arc minute: 1/60th of a degree Arc second:
1/60th of an arc minute Angular diameter: the angle formed by lines extending from the observer to opposite edges of an object Circumpolar constellation: any of the constellations
so close to the celestial poles that they never set (or never rise) from a given location Rotation: motion around an axis passing through the rotating body Revolution: orbital motion
about a point located outside the orbiting body Ecliptic: the apparent path of the Sun around the sky Vernal equinox: the place on the celestial sphere where the Sun crosses the
celestial equator moving northward. Also, the beginning of spring Summer solstice: the point on the celestial sphere where the sun is at its most northerly point. Also the beginning of
summer Autumnal equinox: the point where the sun crosses the celestial equator going southward. Also, the beginning of autumn Winter solstice: the point on the celestial sphere
where the Sun is farthest south. Also, the beginning of winter Perihelion: the orbital point of greatest distance from the sun Solar eclipse: the event that occurs when the moon passes
directly between Earth and the Sun, blocking your view from the sun Umbra: the region of a shadow that is totally shaded Penumbra: the portion of a shadow that is only partially
shaded Annular eclipse: a solar eclipse in which the solar photosphere appears around the edge of the Moon in a bright ring, or annulus. Features of the solar atmosphere cannot be
seen during and annular eclipse. Lunar eclipse: the darkening of the moon when it moves through the earth’s shadow Saros cycle: An 18y, 11 1/3 day period after which the pattern
of lunar and solar eclipses repeats Declination: the angular distance of an object on the celestial sphere measured north + or south from the celestial equator Right ascension: the
angular east-west distance of an objext on the celestial sphere measured from the vernal equinox; is measured in hrs, mins, secs, rather than angular degrees Solar day: the average
time between successive crossings of the sun on the local meridian(24hrs) Sidereal day: the time between successive crossings of any star on the local meridian (23hrs,56mins,
4.09secs) Synodic mnth: the time for a complete cycle of lunar phases (about 29.5days) Sidereal mnth: the time for the moon to orbit earth once relative to any star(about27.3 days)
Sidereal yr: the time for the Earth to complete one full orbit around the sun relative to any star Tropical year (solar yr): the time between successive spring (or autumnal) equinoxes
Apparent solar time: time measured by the location of the sun in the local sky such that noon is when the sun crosses the meridian First principle: something that seems obviously
true and needs no further examination Geocentric universe: a model universe with earth at the center, such as the Ptolemaic universe Uniform circular motion: the classical belief
that the prefect heavens could move only by the combination of uniform motion along circular orbits Parallax: the apparent change in the position of an object due to a change in the
location of the observer. Astronomical parallax is measured in arc seconds Retrograde motion: the apparent backward (westward) motion of the planets as seen against the
background of the stars Epicycle: the small circle followed by a planet in the Ptolemaic theory. The center of the epicycle follows a larger circle (the deferent) around the Earth
Heliocentric universe: a model of the universe with the sun in the center, such as the Copernican universe Paradigm: a commonly accepted set of scientific ideas and assumptions
Ellipse: a closed curve around two points, called the foci, such that the total distance from one focus to the other curve and back to the other focus remains constant Semi-major axis
(a): half of the longest diameter of an ellipse Eccentricity (e): a number between 1 and 0 that describes the shape of an ellipse; the distance from one focus to the center of the ellipse
divided by the semi-major axis Empirical: description of a phenomenon based on only observations, w/o explaining why it occurs Hypothesis: a conjecture, subject to further tests,
that accounts for a set of facts Theory: a system of assumptions and principles applicable to a wide range of phenomena that has been repeatedly verified Natural law: a theory that
has been so well confirmed that it’s almost universally accepted as correct Speed: the rate at which an object moves(changes position); the total distance moved divided by the total
time taken to move that distance Velocity: both the speed and direction of travel of an object Acceleration: the rate of change of velocity with time Mass: a measure of the amount of
matter making up an object Weight: the force that gravity exerts on an object Inverse square relation: a rule that the strength of an effect (such as gravity) decreases in proportion as
the distance squared increases Spring tide: ocean tide of large range that occurs at full and new moon Neap tide: ocean tide of small range occurring at first-and third-quarter moon
Circular velocity: the velocity an object needs to stay in orbit around another object Geosynchronous satellite: a satellite that orbits eastward around Earth with a period of 24hrs and
remains above the same spot of the earth’s surface Centre of mass: the balance point of a body or system of masses. The point about which a body or system of masses rotates in the
absence of external forces Closed orbit: an orbit that repeatedly returns to the same starting point Escape velocity: the initial velocity an object needs to escape from the surface of a
celestial body Open orbit: an orbit that carries an object away, never to return to its starting point
Kepler’s Law: 1) Planetary orbits are ellipses with a sun at the focus 2) The line from the sun to the planet sweeps out equal areas in equal times 3) P2 a3
   
 
 
e =0 (circle) e=1 (flattened ellipse)
 
only holds if d > x
m M = -2.5log (d22/ d11) ; m = apparent magnitude M = absolute magnitude
 
r min = a x = a (1- x/a) = a (1-e) ; r max= a+x = a (1 + x/a) = a (1 + e)
F = mg ; F= GMm / r 2
R= 3r earth
I 1 = P 1 / r12 (joules/sec)
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Document Summary

Milky way: the hazy band of light that circles our sky, produced by the glow of our galaxy spiral arms: long spiral pattern of bright stars, star clusters, gas, and dust. Spiral arms extend from the center to the edge of the disk of spiral galaxies constellation: one of the stellar patterns identified by name, usually of mythological gods, people, animals, or objects. Also, the region of the sky containing that star pattern asterism: a named grouping of stars that is not one of the recognized constellations magnitude scale: the astronomical brightness scale. The larger the number, the fainter the star apparent visual magnitude (mv): a measure of the brightness of a star as seen by human eyes on earth flux: a measure of the flow of energy out of a surface. Also, the beginning of spring summer solstice: the point on the celestial sphere where the sun is at its most northerly point.

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