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Midterm

ASTA01H3 Study Guide - Midterm Guide: Planetesimal, Curve, Lunar Eclipse


Department
Astronomy
Course Code
ASTA01H3
Professor
Kristen Menou
Study Guide
Midterm

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Theory
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 massMilky 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 Ellipses: 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
12:
Iron in the body was produced by carbon fusion in type Ia supernova and the decay of radioactive atoms in the expanding matter expelled by Type 2 supernovae. Solar
nebula theory: a rotating cloud of gas and dust gravitationally collapsed and flattened into a disk around the forming sun at the centre, from which the planets were
formed. Two kinds of planets; terrestrial and jovian. Inner 4 planets are terrestrial, the outer 4 are jovian. Asteroids are small rocky worlds, most orbit the sun in a belt
between mars and Jupiter. Asteroids are debris left over by a planet that failed to form about 3 AU away from the sun. Comets are produced an icy nucleus, the nucleus
remain frozen when far from the sun. As it moves along its elliptical orbit into the inner solar system, sunlight vaporizes the ice releasing gas and dust, solar wind
pushes the gas away forming a tail. The nuclei contain ices of water, co2, co, ch4,nh3, etc. Kuiper belt: the collection of icy planetesimals orbiting in a region from
just beyond Neptune out to 50AU or more. Longer period comets originated from the Oort cloud, a swarm of icy bodies understood to lie in a spherical shell
extending to 100000AU from the sun. Planet formation sarts with condensation, accretion and gravitational collapse. A particle grows by condensation when it
adds matter one atom at a time from its surroundings. Dust grains got bombarded by gas atoms which stuck to the grains. Accretion is the sticking together of solid
particle, dust grains were no more than a few cm apart so they collided frequently and accreted into larger particles. No distinction between a very large grain and a
small planetesimal. Coalescing of planetesimals formed protoplanets, the protoplanets grew by accumulating solid material because they didnt have
enough gravity to trap large amounts of gas. In the warm nebula, atoms of gas were travelling at velocities higher than that of the escape velocity of the
protoplanets so they could only grow by attracting solid bits of ice, rock and metal. Once the protoplanet approached 15
earth masses, it could begin to grow by gravitational collapse, the rapid accumulation from the nebula of large
amounts of infalling gas. According to the solar nebula theory, the Jovian planets began growing by the same
processes that built the Terrestrial planets, but the outer solar nebula contained abundant ices as well as the main solid
bits of metals and silicates.Min distance w/ a and e given + assume e is 0 dmin = (1e)aaE dmax = (1+e)a+aE…….
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