Glossary Flashcards
1
Q
What is absolute magnitude?
A
The apparent magnitude that a star would have if it were seen from a standard distance of 10 parsecs, or 32.6 light-years.
2
Q
What is absolute zero?
A
A temperature equivalent to -273.15 oC; all atoms and molecules stop moving at this temperature.
3
Q
What is an absorption spectrum?
A
Created by gas absorbing light at particular wavelengths that are unique to a chemical.
4
Q
What does accommodation refer to in astronomy?
A
Shape changes in the lens of the eye enabling a person to focus on near and far objects.
5
Q
What is accretion?
A
Material coming together to create, or increase the size of, a celestial object.
6
Q
What is an accretion disc?
A
Material coming on to a spinning star or AGN becomes flattened due to the high spin speed.
7
Q
What is an active galactic nucleus?
A
A supermassive black hole, together with its accretion disc, at the centre of an active galaxy.
8
Q
Define albedo.
A
The reflecting power of a body, from 0 (black) to 100 (a perfect reflector).
9
Q
What does ALSEP stand for?
A
Apollo Lunar Surface Experiments Package.
10
Q
What is an altazimuth mount?
A
A type of telescope mount in which the telescope can be moved freely in both altitude and azimuth.
11
Q
What is altitude in astronomy?
A
The angular distance of a celestial body above the horizon, from 0° at the horizon to 90° at the zenith.
12
Q
Define amplitude.
A
Maximum displacement of a wave measured from the mean position.
13
Q
What is an Ångstrom unit?
A
One hundred-millionth part of a centimetre.
14
Q
What is annihilation in physics?
A
Destruction caused by interaction of a particle with its anti-particle.
15
Q
Define antimatter.
A
Matter made up of anti-particles, such as positrons.
16
Q
What is aphelion?
A
The position of a planet or other body when at its greatest distance from the Sun.
17
Q
What does apogee refer to?
A
The point at which an object is furthest from the Earth in its elliptical orbit.
18
Q
What is apparent magnitude?
A
The brightness of a star as you see it in the night sky (symbol m).
19
Q
Define asterism.
A
A shape within a constellation (often better known than the constellation).
20
Q
What are asteroids?
A
Minor planets that mostly move around the Sun between the orbits of Mars and Jupiter.
21
Q
What is an astronomical unit (AU)?
A
The mean distance between the Earth and the Sun: 149,598,500 km.
22
Q
What is atmosphere in astronomy?
A
The layer of gases surrounding a planet.
23
Q
Define atmospheric pressure.
A
The pressure exerted by the atmosphere of the Earth; at sea level the atmospheric pressure is 100 kPa.
24
Q
What is an atom?
A
The basic ‘building block’ of an element that cannot be chemically broken down.
25
Define atomic number.
The number of protons inside the nucleus of an atom (same as the proton number).
26
What are aurorae?
Glows in the upper atmosphere due to charged particles from the Sun.
27
What does Avogadro’s law state?
Equal volumes of all gases contain an equal number of moles of gas.
28
Define azimuth.
The angular bearing of a celestial object, measured from north (0°) through east (90°), south (180°), and west (270°).
29
What are Baily’s Beads?
The ‘beads’ of light seen near to a total eclipse, caused by sunlight shining through the valleys of the Moon.
30
What is a barred-spiral galaxy?
Galaxies with a nucleus with a bar shape extending either side of the central bulge.
31
What is barycentre?
The centre of gravity of the Earth-Moon system.
32
What is beta-minus (β-) decay?
Emission of an electron from an unstable nucleus.
33
What is beta-plus (β+) decay?
Emission of a positron from an unstable nucleus.
34
What is the Beyer System?
Naming stars in a constellation in order of their brightness, using Greek letters.
35
What is the Big Bang?
An ‘explosion’ approximately 13.8 thousand million years ago that created both space and time.
36
What is the Big Bang theory?
The theory that all matter in the Universe came into existence at the same moment, approximately 13.8 thousand million years ago.
37
What is a binary star?
A star made up of two components, physically associated.
38
What is a black dwarf?
A dead star that has used up all its energy.
39
What is a black hole?
A region around an old, massive, collapsed star from which nothing can escape.
40
What is a blazar?
An AGN with jets of particles that shoot out and point directly towards Earth.
41
What is Bode’s law?
A mathematical series linking the distances of the planets from the Sun.
42
Define bolide.
A meteor that bursts into a fireball.
43
What is a brown dwarf?
A failed star because its mass is too small for a nuclear reaction.
44
What is captured rotation?
When the axial rotation of a body is equal to its revolution period around its primary.
45
What is a Cassegrain reflector?
A type of reflecting telescope that uses a convex secondary mirror.
46
What does CCD stand for?
Charge-coupled device.
47
Define celestial sphere.
An imaginary sphere surrounding the Earth, whose centre is the same as that of the Earth.
48
What is centripetal force?
The resultant force acting at right angles to the velocity of an object that gives rise to circular motion.
49
What is a Cepheid?
A short-period variable star whose variations are perfectly regular.
50
What is the chromosphere?
The part of the Sun’s atmosphere lying above the photosphere, consisting mainly of hydrogen.
51
What are ciliary muscles?
Muscles that help to change the shape of the eye lens.
52
What is a circumpolar star?
A star that never sets from the place of observation.
53
What are stellar clusters?
Groups of stars that have a common origin.
54
What is CMB radiation?
Cosmic microwave background radiation, the ‘left-over’ radiation from the Big Bang.
55
What is colour blindness?
A sex-linked genetic disorder caused by a mutation on the X chromosome.
56
What is a colour index?
A measure of a star’s colour; the difference between the photographic magnitude and the visual magnitude.
57
What are colures?
Great circles on the celestial sphere.
58
What are compressions in sound waves?
Regions where particles are pushed together creating higher pressure.
59
What does conjunction mean in astronomy?
When a planet passes close by a star or another planet in the sky.
60
Define constellation.
A group of stars named after a mythological character or object.
61
What is a continuous spectrum?
The full visible spectrum.
62
What is the convective zone of the Sun?
The upper 500km of the Sun, where energy is brought to the surface by convection currents.
63
What is a converging lens?
A lens that focuses parallel rays of light to a point.
64
What is the Copernican System?
The system in which the Sun is the central body, with the planets moving around it.
65
What is the cornea?
The curved layer over the front of the eye.
66
What is the corona?
The outermost part of the Sun’s atmosphere, made up of thin gas at a very high temperature.
67
What is a coronagraph?
An instrument used to observe the corona even when there is no total solar eclipse.
68
What is a coronal hole?
A region of exceptionally low density in the solar corona.
69
What is a coronal mass ejection?
The largest explosions from the Sun’s surface that fire bursts of plasma into space.
70
What are cosmic rays?
High-speed atomic particles from outer space.
71
What is a cosmic year?
The time taken for the Sun to complete one orbit around the centre of the Galaxy.
72
What is a Coudé system?
An optical system in which the light from the body under observation is received in a fixed direction.
73
What is counterglow?
The faint skyglow known more commonly as the Gegenschein.
74
What is the critical angle?
The angle of incidence in a denser material that gives an angle of refraction equal to 90°.
75
What is culmination?
The maximum altitude of a celestial body above the horizon.
76
What is dark energy?
The energy causing a repelling force in the Universe, making up 73% of it.
77
Define dark matter.
Invisible matter found in space between the galaxies.
78
What is a day in astronomy?
The time taken for the Earth to spin once on its axis.
79
What is deceleration?
Negative acceleration.
80
What is declination?
The angular distance of a celestial body north or south of the celestial equator.
81
What is a degree of arc?
A unit for measuring angles; a full circle contains 360°.
82
Define density.
The density of a substance is found by dividing its mass by its volume.
83
What does dichotomy refer to?
The time of exact half-phase of the Moon, Mercury, or Venus.
84
What is diminished in optics?
An image that is smaller than the object.
85
What is a dioptre?
A unit for the optical power of a lens.
86
What is direct motion in astronomy?
Bodies which move around the Sun in the same sense as the Earth.
87
What is diurnal motion?
The apparent daily rotation of the sky, due to the real rotation of the Earth.
88
What is a diverging lens?
A lens that makes parallel rays of light spread out rather than focus to a point.
89
What is the Doppler effect?
The change in wavelength or frequency of a wave due to relative motion between the source and observer.
90
What is a double star?
A star made up of two components, which may be optical or binary.
91
What is a down quark?
A fundamental particle with a charge of -1/3.
92
What is the Drake equation?
An equation to estimate the number of planets supporting life in our galaxy.
93
What are early type stars?
Stars of spectral type W, O, B and A.
94
What is earthshine?
The dim visibility of the non-sunlit side of the Moon, due to light reflected from the Earth.
95
What does EASEP stand for?
Early Apollo Surface Experiments Package.
96
Define eccentricity in astronomy.
The extent that an orbit or elliptical galaxy differs from a circle.
97
What are lunar eclipses?
The entry of the full moon into the shadow cast by the Earth.
98
What are solar eclipses?
The temporary blotting-out of the Sun when the new moon passes in front of it.
99
What is an eclipsing binary?
A binary system where the components pass regularly in front of each other, causing a drop in apparent magnitude.
100
What is the ecliptic?
The projection of the Earth’s orbit on to the celestial sphere.
101
What are electrons?
Tiny negatively-charged particles within an atom that orbit the nucleus.
102
What are elements in chemistry?
Substances made out of only one type of atom.
103
What is elongation in astronomy?
The apparent angular distance of a planet or comet from the Sun.
104
What is an emission spectrum?
The specific frequencies of light an element emits or gives out.
105
What does EM spectrum stand for?
Electromagnetic spectrum.
106
What are EM waves?
A group of transverse waves that carry different amounts of energy.
107
What is an ephemeris?
A table showing the predicted positions of a moving celestial body.
108
What is an epoch in astronomy?
A date chosen for reference purposes in quoting astronomical data.
109
What is the equation of time?
The interval by which the real Sun is ahead of or behind the mean sun.
110
What is the celestial equator?
The projection of the Earth’s equator onto the celestial sphere.
111
What is equatorial mounting?
A mounting in which the telescope is set upon an axis parallel to the axis of the Earth.
112
What is an equinox?
A point where the ecliptic cuts the celestial equator.
113
What is escape velocity?
The minimum velocity at which an object must move to escape from the surface of a planet.
114
What does EVA stand for?
Extra Vehicular Activity.
115
What is the exosphere?
The outermost part of the Earth’s atmosphere.
116
What is extinction in astronomy?
The dimming of the light from a celestial body when near the horizon.
117
Define extraterrestrial.
A term used to describe things ‘beyond Earth’.
118
What is an eyepiece?
Also known as the ocular.
119
What does EVA stand for?
Extra Vehicular Activity
## Footnote
Refers to activities performed by an astronaut outside a spacecraft.
120
Define Exosphere.
The outermost part of the Earth’s atmosphere
## Footnote
It extends from the thermosphere to outer space.
121
What is extinction in astronomy?
a) When species die out (cease to exist)
b) The dimming of light from a celestial body near the horizon
## Footnote
Extinction varies with the angle of the celestial body above the horizon.
122
What does the term extraterrestrial refer to?
Things ‘beyond Earth’
## Footnote
Often used in the context of life or objects from outside our planet.
123
What is an eyepiece?
The lens at the end of a telescope used for magnifying the image
## Footnote
Also known as the ocular.
124
What are faculae?
Bright, temporary patches above the Sun’s photosphere
## Footnote
Associated with sunspot groups.
125
What is the false colour technique?
The use of colours on an image or chart for analysis
## Footnote
Helps in interpreting data visually.
126
Define far point.
The furthest point the eye can see clearly
## Footnote
Opposite of the near point.
127
What is a finder in astronomy?
A small, wide-field telescope attached to a larger one
## Footnote
Used to help locate target objects.
128
What is a fireball?
An exceptionally bright meteor (above magnitude -5)
## Footnote
Often seen as a shooting star.
129
What does first contact refer to?
When the Moon first starts to cover the disc of the Sun during a total solar eclipse
## Footnote
Marks the beginning of the eclipse.
130
What is the First Point of Aries?
The vernal equinox
## Footnote
The point in the sky where the Sun crosses the celestial equator.
131
What is a flame test?
Heating of metal ions in a flame to produce a colour for identification
## Footnote
Different metals produce different flame colours.
132
What are solar flares?
Brilliant outbreaks in the Sun’s atmosphere usually associated with active spot-groups
## Footnote
Emit charged particles and short-wave radiation.
133
Define focal length.
The distance between the centre of the lens and the focal point
## Footnote
Crucial in determining the magnification of a lens.
134
What is focus in optics?
The point where rays of light meet after convergence by a lens or mirror
## Footnote
Essential for image formation.
135
What is the force of gravity?
An attractive force between all particles that have mass
## Footnote
Fundamental to the structure of the universe.
136
What are Fraunhofer lines?
The dark lines in the spectrum of the Sun
## Footnote
Indicate the absorption of light by elements in the solar atmosphere.
137
What is a free-body diagram?
A diagram showing all the forces acting on an object
## Footnote
Helps in understanding the dynamics of the object.
138
What is free fall?
The normal state of motion of an object in space under central body pull
## Footnote
The Earth is in free fall around the Sun.
139
Define frequency.
The number of vibrations per second
## Footnote
Measured in hertz (Hz).
140
What is friction?
Energy losses caused by two or more objects rubbing against each other
## Footnote
Affects motion and energy efficiency.
141
What is fusion in nuclear physics?
A reaction in which lighter nuclei join together to produce energy
## Footnote
Powers stars, including the Sun.
142
What is a galaxy?
A collection of billions of stars held together by gravity
## Footnote
Example: Milky Way Galaxy.
143
What are Galilean satellites?
The four large satellites of Jupiter: Io, Europa, Ganymede, and Callisto
## Footnote
Discovered by Galileo Galilei.
144
What are gamma rays?
Electromagnetic waves of short wavelength emitted from unstable nuclei
## Footnote
High-energy radiation used in various applications.
145
What is the Gauss?
The standard unit of measurement for a magnetic field
## Footnote
Earth's magnetic field ranges between 0.3 and 0.6 gauss.
146
What does gegenschein refer to?
A faint sky-glow seen opposite to the Sun due to interplanetary material
## Footnote
Caused by sunlight scattering off dust.
147
What is the geocentric model?
Earth-centred model of the Solar System
## Footnote
Predominantly used before the heliocentric model.
148
What is a geostationary orbit?
An orbit maintaining a satellite directly above the same part of the Earth
## Footnote
Useful for communication satellites.
149
What is the gibbous phase?
The phase of a body shining by reflected light when between half and full
## Footnote
Visible during the lunar cycle.
150
Define globular cluster.
Hundreds of thousands of stars tightly clustered together
## Footnote
Often the first generation of stars formed in a galaxy.
151
What is a gnomon?
The pointer on a sundial
## Footnote
Casts a shadow to indicate time.
152
What is the Goldilocks zone?
The region where conditions are right for life around a star
## Footnote
Not too hot, not too cold.
153
What does GPE stand for?
Gravitational potential energy
## Footnote
Energy due to an object's position in a gravitational field.
154
What are solar granules?
Features of the Sun’s photosphere lasting about 10 minutes each
## Footnote
Represent upcurrents in the solar surface.
155
Define gravitation.
The force of attraction that exists between all particles of matter
## Footnote
Fundamental to the structure of the universe.
156
What is a gravitational field?
Gravitational force acting on an object per unit mass
## Footnote
Measured in newtons per kilogram (N/kg).
157
What is a great circle?
A circle on the surface of a sphere whose plane passes through the center
## Footnote
Important for navigation on Earth.
158
What is the Great Dark Spot?
A storm seen on Neptune's surface during the Voyager 2 mission
## Footnote
Has since disappeared, but new dark spots have appeared.
159
What is the Great Red Spot?
A storm on Jupiter observed since the 1600s
## Footnote
It has wind speeds of 350 km/hour.
160
What is the greenhouse effect?
A process where the atmosphere is warmed by infrared radiation re-radiated back to Earth
## Footnote
Essential for maintaining Earth's temperature.
161
What are greenhouse gases?
Gases in the atmosphere responsible for the greenhouse effect, e.g.
* carbon dioxide
* methane
* water vapour
## Footnote
They trap heat in the atmosphere.
162
What is Greenwich Mean Time (GMT)?
The local time at Greenwich, reckoned according to the mean sun
## Footnote
Used as a reference time worldwide.
163
What is the Greenwich meridian?
The line of longitude that passes through the Old Royal Observatory in Greenwich Park
## Footnote
Marks longitude 0°.
164
What is the Gregorian calendar?
The calendar now in use
## Footnote
Introduced by Pope Gregory XIII in 1582.
165
What is a Gregorian telescope?
An obsolete type of reflector telescope with a concave secondary mirror
## Footnote
Provided an erect image.
166
What are H.I and H.II regions?
Clouds of hydrogen in the Milky Way
* H.I: complete hydrogen atoms
* H.II: ionised hydrogen
## Footnote
H.II regions shine as gaseous nebulae.
167
What is Halley’s Comet?
The only bright periodic comet with a period of 76 years
## Footnote
Next due at perihelion in 2061.
168
Define halo, galactic.
The spherical-shaped cloud of stars around the Galaxy
## Footnote
Contains older stars and globular clusters.
169
What is the Harvest Moon?
The full moon nearest to the autumnal equinox
## Footnote
Traditionally signifies the harvest season.
170
What is heliacal rising?
The rising of a celestial body at the same time as sunrise
## Footnote
Indicates the first visibility in the dawn sky.
171
What is the heliocentric model?
Sun-centred model of the Solar System
## Footnote
Proposed by Copernicus.
172
What is helium?
The second lightest element with two electrons
## Footnote
Commonly found in stars.
173
What is the Hoba meteorite?
The biggest meteorite in the world, weighing 60 tonnes
## Footnote
Found in Namibia.
174
What is the horizon in astronomy?
The great circle on the celestial sphere 90° from the zenith
## Footnote
Defines the observable universe from a location.
175
What is hour angle?
The time that has passed since a celestial object crossed the meridian
## Footnote
Important for celestial navigation.
176
What is the hour circle?
The great circle on the celestial sphere passing through both celestial poles
## Footnote
Key for determining local time.
177
What is the H-R Diagram?
The Hertzsprung-Russell Diagram plotting stars by spectral types and absolute magnitudes
## Footnote
Useful for understanding stellar evolution.
178
What is the Hubble constant?
A constant relating the recessional velocity of galaxies
## Footnote
Usually taken as 77 km/s/Mpc.
179
What is Hubble time?
The time elapsed since the origin of the Universe
## Footnote
Related to the expansion of the universe.
180
What is the Hunter’s Moon?
The full moon following the Harvest Moon
## Footnote
Traditionally marks the beginning of hunting season.
181
What is immersion in astronomy?
The entry of a celestial object into occultation or eclipse
## Footnote
Important for observing celestial events.
182
What is inferior conjunction?
The position of an inferior planet when between the Earth and the Sun
## Footnote
Applies to Mercury and Venus.
183
Define infrared radiation.
Electromagnetic radiations with wavelengths between 10^-6 and 10^-4 metres
## Footnote
Associated with thermal energy.
184
What are infrared waves?
Non-ionising waves with wavelengths longer than red light
## Footnote
Carry radiant heat.
185
What is intensity in terms of radiation?
The power of radiation per unit area
## Footnote
Measured in watts per square meter.
186
What is interplanetary dust?
Dust particles from old comet tails or asteroids left in space
## Footnote
Burns up upon entering Earth's atmosphere.
187
What is the inverse square law?
A relationship where doubling one quantity reduces the related quantity by a factor of four
## Footnote
Commonly seen in gravitational and light intensity calculations.
188
Define ion.
An atom with an electrical charge due to gaining or losing electrons
## Footnote
Can be positive or negative.
189
What is ionisation?
A process where radiation transfers energy to liberate an electron from an atom
## Footnote
Fundamental in various chemical and physical processes.
190
What is ionisation energy?
The energy required to remove an electron from an atom
## Footnote
Varies for different elements.
191
What is an ion tail?
The straight, gaseous tail of a comet
## Footnote
Formed by the solar wind.
192
What is the ionosphere?
The region of the Earth’s atmosphere above the stratosphere containing charged particles
## Footnote
Important for radio wave propagation.
193
What does IRAS stand for?
Infra-Red Astronomical Satellite
## Footnote
Launched to study infrared radiation from celestial objects.
194
What is the iris?
The coloured part of the eye that controls light entry
## Footnote
Adjusts the size of the pupil.
195
What is an irregular galaxy?
Galaxies that do not fit into any classification
## Footnote
Often formed from the collision of two galaxies.
196
What is an isophote?
A line on a diagram joining all points of equal density or intensity
## Footnote
Used in various fields, including astronomy.
197
What are isotopes?
Nuclei of atoms with the same number of protons but different numbers of neutrons
* a) Same protons, different neutrons
* b) Atoms with same proton number, different neutron numbers
## Footnote
Important in nuclear chemistry and dating methods.
198
What is a Julian day?
A count of days from 12 noon on 1 January 4713 BCE
## Footnote
Used in astronomy for timekeeping.
199
What is a joule?
The unit of work done and energy
## Footnote
Defined as the work done when a force of 1 N moves a distance of 1 m.
200
What is the Kelvin scale?
A temperature scale where temperature is measured in Kelvin (K)
## Footnote
Absolute temperature scale.
201
What are Kepler’s laws?
Three important Laws of Planetary Motion announced by Johannes Kepler
## Footnote
Fundamental to celestial mechanics.
202
What is a kiloparsec?
One thousand parsecs (3260 light-years)
## Footnote
Used in measuring astronomical distances.
203
What is kinetic energy?
The energy that moving objects have
## Footnote
Calculated as KE = 1/2 mv².
204
What is a lander?
A robotic space probe sent to planets and moons for soil analysis
## Footnote
Used in planetary exploration missions.
205
What are late-type stars?
Stars of spectral types M, R, N, and S
## Footnote
Typically cooler and redder than early-type stars.
206
Define latitude.
The angle of a location above or below the equator
## Footnote
Measured in degrees.
207
What is the lens equation?
Relates image distance v, object distance u, and focal length f: (1/u) + (1/v) = (1/f)
## Footnote
Essential for lens calculations.
208
What are librations?
The apparent tilts enabling us to see 59 percent of the Moon’s surface from Earth
## Footnote
Occur due to the Moon's elliptical orbit.
209
What is a life cycle in astronomy?
The journey of a star in time
## Footnote
Includes formation, evolution, and eventual death.
210
What is a light-curve?
A graph showing the changing brightness of a variable star
## Footnote
Used to study stellar variability.
211
What is light energy?
Energy due to light (electromagnetic) waves
## Footnote
All glowing objects emit light energy.
212
What is a light-year?
The distance travelled by light in one year: 9.4607 million million kilometres
## Footnote
Used to measure astronomical distances.
213
What does LM stand for?
Lunar Module
## Footnote
Used in Apollo missions to land on the Moon.
214
What is the Local Group?
The group of galaxies of which our Galaxy is a member
## Footnote
Includes over 54 galaxies.
215
What are longitudinal waves?
Waves with vibrations parallel to the direction they travel
## Footnote
Example: sound waves.
216
What does LRRR stand for?
Laser Ranging Retroreflector
## Footnote
Used to measure distances to the Moon.
217
What is luminosity?
The brightness/magnitude of a star or celestial object
## Footnote
Measured in watts.
218
What is a lunation?
The interval between successive new moons: 29d 12h 44m
## Footnote
Important in lunar calendars.
219
What is magma?
Hot molten rock found in the mantle below the Earth’s surface
## Footnote
Can form igneous rocks when cooled.
220
What is a magnetic storm?
A sudden disturbance of the Earth’s magnetic field
## Footnote
Caused by solar flares.
221
What is the magnetosphere?
The area around a celestial body where its magnetic field is dominant
## Footnote
Protects the planet from solar winds.
222
What is magnification?
The magnification of a telescope can be adjusted by changing the eyepiece
## Footnote
Calculated by the focal length of the objective / focal length of the eyepiece.
223
What does magnified mean?
An image that is larger than the object
## Footnote
Commonly referred to in optics.
224
Define magnitude in astronomy.
a) Apparent: brightness of a celestial body
b) Absolute: brightness at 10 parsecs
c) Photographic: measured from a photographic plate
## Footnote
Lower magnitude indicates a brighter object.
225
What is the Main Sequence?
The belt on the H-R Diagram running from upper left to lower right
## Footnote
Most stars lie in this region.
226
What is a Maksutov telescope?
An astronomical telescope that uses both mirrors and lenses
## Footnote
Known for its compact design.
227
What is the mantle of the Earth?
The semi-liquid layer beneath the crust
## Footnote
Composed of silicate rocks.
228
Define mass.
The amount of matter inside an object, measured in kilograms
## Footnote
Does not change regardless of location.
229
What is the mass-energy equation?
Einstein’s equation E = mc²
## Footnote
Links mass with energy.
230
What is the mass number?
Total number of protons and neutrons within the nucleus of an atom
## Footnote
Also known as the nucleon number.
231
What does matter refer to?
Anything that has mass and volume
## Footnote
Comprises all physical substances.
232
What is the Maunder minimum?
The period between 1645 and 1715 when sunspots were rare
## Footnote
Associated with a colder climate.
233
What is the mean in mathematics?
The midpoint in an arithmetic progression
## Footnote
Commonly referred to as the average.
234
What is the mean sun?
An imaginary body travelling eastward along the celestial equator
## Footnote
Used for calculating time zones.
235
Define melting point.
The temperature at which a solid becomes a liquid
## Footnote
Varies for different substances.
236
What is the celestial meridian?
The great circle on the celestial sphere passing through the zenith and both celestial poles
## Footnote
Cuts the observer’s horizon at north and south points.
237
What are Messier numbers?
Numbers allotted to clusters and nebulae in Charles Messier's catalogue
## Footnote
Used for identifying astronomical objects.
238
What is the mesosphere?
Part of the ionosphere at an altitude of 50 km to 80 km above Earth
## Footnote
Region where meteors burn up.
239
What is a meteor?
A small particle seen when it enters the Earth’s upper atmosphere
## Footnote
Often referred to as a shooting star.
240
What is a meteorite?
A solid body that strikes the Earth from space
## Footnote
Composed of iron, stone, or a mixture.
241
What is a meteoroid?
Chunks of rock in space orbiting the Sun
## Footnote
Varies in size from small to large.
242
What are micrometeorites?
Extremely small particles not massive enough to produce luminous effects
## Footnote
Often burn up upon entering the atmosphere.
243
What is a micron?
A unit of length: one-thousandth of a millimetre
## Footnote
Symbol: μ.
244
What are microwaves?
Electromagnetic radiations intermediate between infrared and radio waves
## Footnote
Wavelengths range from 1 mm to 1 metre.
245
What is the Milky Way?
The luminous band crossing the sky, looking along the main plane of the Galaxy
## Footnote
Contains our Solar System.
246
What are minerals?
Solid metallic or non-metallic substances found naturally in the Earth’s crust
## Footnote
Essential for various geological processes.
247
What are minor planets?
Another name for asteroids
## Footnote
Smaller celestial bodies orbiting the Sun.
248
What is a minute of arc?
One-sixtieth of a degree
## Footnote
Used in angular measurements.
249
What are Mira stars?
Variable stars with periods of a few hundred days
## Footnote
Notable for their brightness changes.
250
What is the Greek letter for the symbol μ?
Mu
251
Define microwaves.
Electromagnetic radiations, intermediate between infrared and radio waves; wavelengths 1 mm to 1 metre.
252
What is the Milky Way?
The luminous band crossing the sky, due to the fact that in this direction we are looking along the main plane of the Galaxy.
253
What are minerals?
Solid metallic or non-metallic substances found naturally in the Earth’s crust.
254
What is another name for asteroids?
Minor planets
255
What is a minute of arc?
One-sixtieth of a degree.
256
Define Mira stars.
Variable stars with periods of a few weeks or months, named after the prototype star, Mira Ceti.
257
What is a molecule?
A stable association of atoms.
258
How is momentum calculated?
By multiplying the mass of an object by its velocity.
259
What is a calendar month?
The civil month – 30 or 31 days (28 or 29 in February).
260
What is sidereal month?
The time taken for the Moon to complete one orbit (27.32 days).
261
What are moving clusters?
Groups of stars sharing a common motion through space.
262
What defines a multiple star?
A star made up of more than two physically-associated components.
263
What does NASA stand for?
The National Aeronautics and Space Administration (USA).
264
What is the NGC?
The New General Catalogue of Clusters and Nebulae, compiled by J.L.E. Dreyer.
265
What is a nadir?
The point on the celestial sphere immediately below the observer.
266
Define a nanometre.
One thousand millionth of a metre.
267
What is a neap tide?
The tide produced when the Sun and Moon are at right angles to the Earth.
268
What is a nebula?
A mass of ‘dust’ and tenuous gas in space.
269
What is a neutrino?
A fundamental particle with no electrical charge and, apparently, no rest mass.
270
What is a neutron?
A fundamental particle with no electrical charge, but a mass practically equivalent to that of a proton.
271
What is a neutron star?
A star made up mainly of neutrons, the remnant of a supernova outburst.
272
What is a Newtonian reflector?
The most common type of reflecting telescope.
273
State Newton’s first law.
A body will remain at rest or continue to travel at a constant velocity unless acted on by an external force.
274
State Newton’s second law.
Force = mass x acceleration.
275
State Newton’s third law.
When two bodies interact, each exerts an equal and opposite force on the other.
276
What are nodes in orbital mechanics?
The points at which the orbit of the Moon, a planet, comet, or asteroid cuts the plane of the ecliptic.
277
What is a nova?
A stellar outburst in the white dwarf component of a binary system.
278
Define nuclear energy.
Energy that is stored inside the nuclei of atoms.
279
What is nuclear fusion?
The fusing together of hydrogen nuclei to produce helium nuclei.
280
What is a nucleon?
A term used to refer to either protons or neutrons.
281
What is nucleon number?
Total number of protons and neutrons within the nucleus of an atom.
282
What is the nucleus of an atom?
The central core of an atom, which contains protons and neutrons and has a positive charge.
283
What is an object-glass in telescopes?
The main lens of a refracting telescope.
284
Define obliquity of the ecliptic.
The angle between the ecliptic and the celestial equator: 23o26’24”.
285
What is occultation?
The covering-up of one celestial body by another.
286
What is Olbers’ paradox?
A paradox discussing why the sky is dark at night.
287
What is the Oort cloud?
A theory of a cloud of comets orbiting the Sun at a distance of about a light-year.
288
What is an open cluster?
A loose galactic cluster of stars.
289
What is opposition in astronomy?
The position of a planet when exactly opposite the Sun in the sky.
290
What is an optical double?
A double star in which the two components are not genuinely associated.
291
How is optical power calculated?
Using ‘1/focal length of the lens in metres’.
292
What is an optical window?
The region of the electromagnetic spectrum in which radiations can pass through the atmosphere.
293
What is an orbit?
The path of a celestial body.
294
What is an orrery?
A model showing the Solar System with movable planets.
295
Define parallax, trigonometrical.
The apparent shift of an object when observed from two different directions.
296
What is a parsec?
The distance at which a star would show a parallax of 1 second of arc; 3.26 light-years.
297
What is a peak in wave terminology?
Uppermost point of a wave.
298
What is peer review?
The process of evaluating the quality of research using anonymous reviews by experts.
299
What is a penumbra?
The area of partial shadow to either side of the main cone of shadow cast by the Earth.
300
What is perigee?
The position of the Moon in its orbit when closest to the Earth.
301
What is perihelion?
The position of a body in the Solar System when at its closest to the Sun.
302
What are perturbations?
The disturbances in the orbit of a celestial body produced by the gravitational pulls of other bodies.
303
What is a phase in terms of celestial bodies?
Non-circular shape that includes a crescent.
304
What is the phase angle?
The angle between the Earth and the Sun, as seen from another body in space.
305
What is a photoelectric cell?
An electronic device that produces an electric current when light falls upon it.
306
What is a photoelectric photometer?
An instrument used for measuring the brightness of celestial objects.
307
What is photography?
The process of producing permanent images.
308
What is a photon?
The smallest ‘unit’ of light.
309
What is the photosphere?
The bright surface of the Sun.
310
What are plages, solar?
Brighter regions on the Sun’s surface, observed in the light of one element only.
311
What is a planetary nebula?
A small, hot dense star surrounded by a shell of gas.
312
Define plasma.
Gas in which the atoms are wholly ionised.
313
What is Pogson’s ratio?
The ratio between the brightness of two stars at successive magnitudes.
314
What is a polar orbit?
An orbit where a satellite passes regularly over the north and south poles.
315
Define the celestial poles.
The north and south points of the celestial sphere.
316
What are stellar populations?
Two main types of star regions: * (I) hot and white stars; (II) old red giants and supergiants.
317
What is the position angle?
The apparent direction of one object with reference to another.
318
What is a positron?
The anti-particle of an electron with a positive charge.
319
What is power in physics?
The rate of work done or the rate of energy transfer.
320
Define precession.
The apparent slow movement of the celestial poles.
321
What is the prime meridian?
The meridian on the Earth’s surface that passes through both poles.
322
What is the principal focus in optics?
The point at which rays of light parallel to the principal axis of a converging lens converge.
323
State the principle of conservation of energy.
Energy cannot be created or destroyed, it can be transferred from one form to another.
324
State the principle of conservation of momentum.
The total momentum before and after a collision remains the same.
325
What is a prism?
A block of glass used to split white light into a visible spectrum.
326
What are prominences?
Masses of glowing gas, mainly hydrogen, rising from the Sun’s surface.
327
What is proper motion?
The individual motion of a star on the celestial sphere.
328
What are protons?
Small positively-charged particles found in the nucleus of an atom.
329
What is proton number?
Number of protons inside the nucleus of an atom.
330
What is a protoplanetary disc?
A disc of dust seen around a protostar from which planets form.
331
What is a protostar?
A fragment of a nebula which gives off light as a star begins to form.
332
What is the Ptolemaic System?
The old geocentric theory of the Solar System.
333
What is a pulsar?
A rapidly-rotating neutron star, sending out pulsed radio waves.
334
What is a pulsating variable star?
A variable star in which the changes are intrinsic.
335
What is the pupil in the human eye?
The central hole produced by the iris.
336
What is a P wave?
Primary (longitudinal) seismic wave.
337
What does QSO stand for?
Quasi-Stellar Object.
338
What is a quadrant in astronomy?
An astronomical measuring instrument used in ancient times.
339
What is quadrature?
The position when the Moon or a planet is at right angles to the Sun as seen from the Earth.
340
What is quantum in terms of light?
The energy possessed by one photon of light.
341
What is a quark?
A fundamental particle within particles such as neutrons and protons.
342
What is a quasar?
A very remote, super-luminous object; probably the core of a very active galaxy.
343
What is radial velocity?
The towards-or-away movement of a celestial body.
344
Define radiant in meteorology.
The point in the sky from which the meteors of any particular shower appear to radiate.
345
What is radiation?
Any form of energy that originates from a source.
346
What is the radiative zone of the Sun?
The zone that radiates heat from the Sun’s core to within 500 km of its surface.
347
What are radioactive isotopes?
Atoms with the same number of protons but different numbers of neutrons with an unstable nucleus.
348
What is a radio telescope?
An instrument used for collecting and analysing natural radio waves from space.
349
What is the radio window?
The region of the electromagnetic spectrum that is transparent to radio waves from space.
350
What is a radius vector?
An imaginary line joining the centre of a planet to the centre of the Sun.
351
What are rarefactions in sound waves?
Regions where particles are pulled apart and create regions of low pressure.
352
What is Rayleigh scattering?
The colours in the sky produced by the atmosphere scattering light.
353
What is a real image in optics?
Image formed on the other side of the lens to the object.
354
What is a recurrent nova?
A star that has been known to suffer more than one nova outburst.
355
What is a red giant?
A huge expanded star with a cooler surface.
356
What is red-shift?
The apparent increase in wavelength of the light of a body that is receding from the observer.
357
What is a reflecting telescope?
An optical telescope in which the light from the target object is collected by a curved mirror.
358
What is reflection?
When a wave is bounced off a surface.
359
What is refraction?
The bending of a ray of light when passing through a transparent surface.
360
What is a refractor telescope?
A telescope in which the light from the target object is collected by a lens.
361
What is regolith?
The outermost layer of the surface of the Moon or planetary body.
362
What is resolving power?
The ability of a telescope to separate objects that are close together.
363
What is retardation in astronomy?
The difference in the time of moonrise on successive nights.
364
What is the retina?
Covering of light-sensitive cells at the back of the eyeball.
365
What is retrograde motion?
Orbital or rotational movement in the opposite sense to that of the Earth’s movement.
366
What is a reversing layer?
The gaseous layer above the Sun’s bright surface responsible for the Fraunhofer lines.
367
What is right ascension (RA)?
The angular distance of a star from the vernal equinox, measured westward.
368
What is a rill?
Crack-line feature on the Moon’s surface.
369
What are rods and cones?
Different types of photoreceptor.
370
What are RR Lyrae variables?
Variable stars with regular light curves and very short periods of a day or less.
371
What does RTG stand for?
Radioisotope Thermoelectric Generator.
372
What are satellites in astronomy?
Minor bodies orbiting planets.
373
What is a scalar quantity?
A quantity that only has size or magnitude.
374
What is a Schmidt telescope?
A type of telescope using a spherical mirror together with a special correcting plate.
375
What are scientific conferences?
Meetings where participants exchange and present new ideas for research.
376
What are scientific journals?
Periodic publications with articles contributed to by scientists.
377
What is scintillation?
The official name for ‘twinkling’ of a star or other celestial body.
378
What is secular acceleration?
The apparent speeding-up of the Moon in its orbit.
379
What are seismic waves?
Shock waves from earthquakes.
380
What is a seismometer?
An earthquake-detecting instrument.
381
What are Seyfert galaxies?
Galaxies with small, bright nuclei and weak spiral arms.
382
What is a shooting star?
The popular name for a meteor.
383
What is a sidereal period?
The time taken for a body to complete one orbit round its primary.
384
What is sidereal time?
The local time measured according to the apparent rotation of the celestial sphere.
385
What is Snell’s law?
An equation relating the angle of incidence and refraction in different media.
386
What is a solar day?
From noon one day to noon the next.
387
What is the time taken for a body to complete one orbit around its primary with the Earth?
365.25 days
388
Define sidereal time.
The local time measured according to the apparent rotation of the celestial sphere.
389
What does Snell’s law relate?
The angle of incidence, angle of refraction, and the refractive index of a medium.
390
What is a solar day?
From noon one day to noon the next day.
391
What does the Solar System consist of?
The Sun and all the objects orbiting it.
392
What is solar time?
Local time, reckoned according to the mean sun.
393
What is solar wind?
A flow of charged particles streaming out from the Sun.
394
When do solstices occur?
When the Sun is at its northernmost or southernmost point in the sky.
395
What does a spectrometer do?
Analyzes light from various sources.
396
What is the function of a spectroscope?
Splits up light from a light-source using a prism or diffraction grating.
397
What is spectroscopy?
A sophisticated type of flame test that produces a unique emission spectrum.
398
Define a spectroscopic binary.
A binary system whose components are detected spectroscopically.
399
What is a speculum in astronomy?
The main mirror of a reflecting telescope.
400
How is speed calculated?
Speed = distance / time.
401
What shape is the Earth?
Oblate spheroid.
402
What is a spring tide?
The tide produced when the Sun and Moon are aligned.
403
What is the Steady State theory?
The theory that the Universe has always existed and creates new material spontaneously.
404
Where is the stratosphere located?
Between the troposphere and the ionosphere.
405
What is the strong nuclear force?
An attractive force between all neutrons and protons.
406
What is the style of a sundial?
The pointer or gnomon.
407
What stars make up the summer triangle?
* Vega * Deneb * Altair
408
What are sunspots?
Dark areas on the Sun's surface caused by magnetic effects.
409
What is a superior planet?
A planet moving around the Sun at a distance greater than that of the Earth.
410
What is a supernova?
A stellar explosion.
411
What is an S wave?
A secondary (transverse) seismic wave.
412
What is the synodic period?
The interval between successive oppositions of a superior planet.
413
Define syzygy.
The position of the Moon in its orbit when new or full.
414
What are tektites?
Small, glassy objects found on Earth, possibly of terrestrial origin.
415
What is the terminator in astronomy?
The boundary between the daylit and night hemispheres of a celestial body.
416
What is the thermosphere?
Part of the ionosphere at an altitude of 80 km to 120 km.
417
What is transit in astronomy?
The passage of a celestial object across the observer’s meridian.
418
What is the troposphere?
The lowest region of the Earth’s atmosphere.
419
What is ultraviolet radiation?
The region of the electromagnetic spectrum between 10^-8 and 4 x 10^-7 metres.
420
Define umbra.
The dark, inner part of a shadow cast by a celestial object.
421
What does the Universe encompass?
The whole of space containing all the galaxies.
422
What is an up quark?
A fundamental particle with a charge of +2/3.
423
What is a vacuum?
Empty space that has no particles.
424
What are Van Allen zones?
Zones around the Earth where charged particles are trapped by its magnetic field.
425
What are variable stars?
Stars that change in magnitude over relatively short periods.
426
Define vector.
A quantity that has both magnitude and direction.
427
What is velocity?
Speed in a certain direction.
428
What is the vernal equinox?
The First Point of Aries.
429
What is the Virgo Cluster?
A cluster of over 2,000 galaxies spread over a diameter of about 10 million light years.
430
What is a virtual image?
An image formed on the same side of the lens as the object.
431
What is a watt?
The unit of power equal to one joule per second.
432
What is the wave equation?
Speed = frequency x wavelength.
433
What is wavelength?
Distance between neighboring wave peaks.
434
What is weight?
The gravitational force acting on an object.
435
Define white dwarf.
A small, very dense star that has exhausted its nuclear power.
436
What is Wien’s law?
The relationship between the peak emission wavelength of a star and its temperature.
437
What is the Wilson effect?
The foreshortening of a sunspot near the solar limb.
438
What is work done in physics?
The product of force and distance moved in the direction of the force.
439
What are wrinkle ridges?
Wavy, raised markings seen on the surface of lunar Maria.
440
What is X-ray radiation?
Electromagnetic radiation with wavelengths between 10^-12 meters and 10^-8 meters.
441
What is a year in terms of Earth's orbit?
The time taken for the Earth to complete one orbit around the Sun.
442
What is zenith?
The observer’s overhead point.
443
Define zenith hourly rate.
The expected number of meteors from a shower under ideal conditions.
444
What is zenith distance?
The angular distance of a celestial body from the zenith.
445
What is the zodiac?
A belt around the sky where the Sun, Moon, and planets are found.
446
What is zodiacal light?
A cone of light rising from the horizon along the ecliptic.
447
What is the Zürich number?
A measure of sunspot activity.
