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Astronomy > Terms and Definitions > Flashcards

Terms and Definitions Flashcards

1
Q

Celestial Sphere

A

imaginary sphere of infinite radius centred on the earth in which all celestial bodies are assumed to be projected

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2
Q

ecliptical

A

the path the sun traces in the sky during one year

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3
Q

vernal equinox

A

the point where the sun crosses the celestial equator, south to north, occurs in march marks the first day of spring in the northern hemisphere

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4
Q

autumnal equinox

A

the point where the sun crosses the celestial equator , occurs in september when the sun enters the southern hemisphere

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5
Q

right asension

A

the celestial equivalent to terrestrial longitude, moves eastward, 24 hours is one circle, the point where the sun crosses the celestial equator on the vernal equinox is 0 hour

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6
Q

declination

A

comparable to laittitude measured in degrees north and south of the equator , north is postive and south is negative

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7
Q

summer and winter solstice

A

june, sun is over the tropic of cancer, december sun is over the tropic of capricorn

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8
Q

the big bang

A

1929, mt wilson observaotry, edwin hubble determined that the farther away a galaxy is from earth the faster it appeasr to move away, this notion of ‘expanding universe’ the universe began with an intense burst of energy at a single moment in time and has been expanding ever since, 13.8 billion years

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9
Q

dark energy

A

albert einstein 1917. the expansion of the universe is accelerating caused by dark energy

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10
Q

dark matter

A

hypothetical form of matter accounting for approximately 85% of the matter in the universe. implied through gravitational effects. not discovered yet. dark because it does not emit, reflect, absorb em radiation so difficult to detect.

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11
Q

interstellar medium

A

the matter and radiation that exist in the space between star systems in a galaxy, includes gas in atomic, ionic and molecular forms and dist and cosmic rays. it ills interstellar space (closest to an absolute vacuum) and blends smoothly into the intergalactic space.

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12
Q

molecular clouds

A

coldest, densest clouds in the interstellar medium, formation of stars, made of dust and hydrogen gas. located primarily in the disk of spiral galaxies and active regions of irregular galaxies

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13
Q

star formation

A

dust and gas collects and clumps together which attracts more materials. the mass, temperature and pressure will increase and hydrogen gas fuses to form helium. this thermo nucler reaction provides the nergy for the star

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14
Q

protoplanetary disk

A

is the rotating circumstellar disc of dist and gas surrounding the newly young star

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15
Q

protoplanets

A

large planetary embryo orginated within the protoplanetary disk that undergone internal melting to produce a differentiated interior
Protoplanets are thought to form out of kilometer-sizedplanetesimalsthat gravitationally perturb each other’s orbits and collide, gradually coalescing into the dominantplanets.

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16
Q

accretion and accretion disc

A

accummulation of matter by a star or other clestial object, strucure formed by diffuse material in orbital motion around a massive central body.

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17
Q

stellar black hole

A

formed by the gravitational collapse of a star , wighs 5 to several 10s of solar masses

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18
Q

supermassive black hole

A

largest type of black hole, formed during the big bang and lie within the centre of active galaxies, millions ot billions times the mass of the sun

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19
Q

the solar system

A

the gravitationally bound system of the sun and the planets that orbit it, the sun and the largest of the 8 planets and the dwarf planets and the small system bodies

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20
Q

planets

A

a astronomical body orbiting a star that is massive enough to be rounded by its own body but not massive enough to cause thermonuclear fusion and has cleared its neighbouring region of planetisimals

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21
Q

dwarf planets

A

a round celestial body orbitng the sun but has not cleared its neighbouirng region from other objects pluto, eris, makemake, haunmea , ceres

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22
Q

minor planets

A

astronomical object in direct orbit of the sun that is neither a planet or comet

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23
Q

Trans neptunion objects

A

any minor or dwarf planet that orbits the sun at a greater average distance than neptune, 30AU

24
Q

plutoids

A

round celestial bodies that in orbit around the sun at agreater distance than neptune and have notcleared their neigbourhood arou d their orbit, round TNO that have not cleared their path

25
Q

small solar system bodies

A

object in the solar system that is not a planet, natural satellite or dwarf planet
They include comets, asteroids, andscattered discobjects,
with the exception of the dwarf planets andtrans-Neptunian objects.

The orbits of the vast majority of small Solar System bodies are located in theasteroid beltand theKuiper belt.

26
Q

centaur

A

exibits characterisitcs of both asteriod and comet, revolve around the sun in the outer solar system between the orbits of jupiter and neptune

27
Q

Near earth object

A

a small solar system body whose orbit brings it tino proximity with earth 1.3 AU

28
Q

potentially hazardous object

A

a neo crosses the earths and is larger than 140 meters

29
Q

constellation

A

an area of the celestial sphere, 88

30
Q

zodiacal constellations

A

the apparent path of the sun across the heavens through the constellations that divide the ecliptic into 12 equal zones of celestial longitude

31
Q

precession

A

the change in direction of the earths axis and the effect on astronomical observations, 26000

32
Q

first point of ares

A

the vernal equinox was first called the first point of ares by hipparchus in 130BC because the sun crossed the clestial equautor of the constellation ares, now due to the precession the sun crosses the celestial equtor of the pisces and soon aquarius

33
Q

aphelion and perihelion

A

aphelion is the furthest point on the earths orbit from the sun july , perihelion is the closest point of the earths orbit to the sun january.

34
Q

perigee and apogee

A

orbits around the earth

35
Q

side real day

A

length of time which passes between a given distant star and in the sky crossing the meridian

36
Q

solar day

A

lenth of time which passes between the sun reaching its highest point in the sky two consecutive times, synodic day

37
Q

eclipse

A

when a body siappears or partially disappears from view, wither by an occulation as with a solar eclipse or kunar eclipse where its cast into the shadow of another

38
Q

transits and occulatations

A

tranist occurs when a smaler body passes in front of a larger one , occulateion is when an apparent larger body passes in front of a apparent smaller body

39
Q

astronomical unit

A

mean distance between the earth and the sun = 149.6 million km

40
Q

luminosity

A

the amount of light emitted by a star

41
Q

lunation

A

the bright part of the moon always faces towards the sun

42
Q

terminator

A

the boundary of the light side and dark sidr of a planet or other body

43
Q

libration

A

the rocking motion of the moon, it makes 59 % of the moon visible from earth

44
Q

ejecta

A

the material from beneath a body that is ejected by an impact and distributed around the surface

45
Q

opposition

A

the postion of a planet when it is exactly opposite the sun, best time for observing

46
Q

elongation

A

the angular distance brom the sun as seen from the earth, max elongation for mercury is 18-28 and venus is 45-47. varies due to elliptical orbit

47
Q

eastern and western elongation

A

inferior planet is visible after sunset greatest eastern elong bisible before sunrise is greatest westen elong

48
Q

apparition

A

the appearance of a comet in the sky or period in which a planet is observable

49
Q

asterism

A

a small group of easily recognnizable stars not forming a complete constellations

50
Q

albedo

A

ratio of reflected to incidetn light,how strongly it reflects light from light sources , 0 to 1

51
Q

radiant

A

point in sky which metors in metoer showers seem to originate

52
Q

parallax angle

A

if we look at the position of a star against a a distance background it would h=appear to have moved 6 months later when the earth has shifted its position, change in view

53
Q

parsec

A

use 1 AU as the base of a triangle and the parallex angle is (1 arcsecond, the height is 1 parsec)= 3.26 light years to measure stellar distances

54
Q

parsec formula

A

the reciprocal of its parallex error where d is distance to star , smaller parallax angle the further away the star

55
Q

pertubation

A

when multiple objects are present in one system the gravitationalforces affect eachother cauing slight disturbances in their path around a central object, changes the object parameters

56
Q

conjunction

A

an event that occurs when two or more objects appear close together in the sky

57
Q

great conjunction

A

when jupiter overtakes saturn in its orbit, they appear closest together in the sky, happens 20 years the rarest conjunction of naked eye planets

Astronomy (2 decks)

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