1
Q
What is an Astronomical Unit (AU)?
A
The average distance between Earth and the Sun — about 150 million km (1.5 × 10⁸ km).
2
Q
What is a light-year (ly)?
A
The distance light travels in one year — about 9.5 trillion km (9.5 × 10¹² km).
3
Q
Size of the Solar System?
A
~1 × 10¹⁰ km (≈ 60 AU).
4
Q
What is a star?
A
A large, glowing ball of gas that generates heat and light through nuclear fusion
5
Q
What is a planet?
A
A moderately large object orbiting a star that shines by reflected light; may be rocky, icy, or gaseous.
6
Q
What is a moon (satellite)?
A
An object that orbits a planet.
The Moon is a type of satelite
7
Q
What is an asteroid?
A
A relatively small, rocky object that orbits a star.
8
Q
What is a comet?
A
A small, icy object that orbits a star.
9
Q
Define solar system (star system).
A
A star and all material that orbits it, including planets and moons.
10
Q
What is a nebula?
A
An interstellar cloud of gas and/or dust.
11
Q
What is a galaxy?
A
A massive island of stars in space held together by gravity, orbiting a common center.
12
Q
What is a galaxy group?
A
A few dozen galaxies bound by gravity, a few million light-years across.
13
Q
What is a galaxy cluster?
A
A group of a few hundred to a few thousand galaxies
14
Q
What evidence shows that the universe is expanding?
A
Distant galaxies are moving away from us; the farther they are, the faster they recede.
15
Q
What is the Big Bang?
A
The origin of the universe, marking the beginning of its expansion.
16
Q
What elements were formed in the Big Bang?
A
Hydrogen and helium (plus traces of lithium, beryllium, boron).
17
Q
How did heavier elements form?
A
By nuclear fusion inside stars and in supernovae or neutron-star mergers.
18
Q
Why are humans considered “star-stuff”?
A
Our bodies are made of elements created inside stars and recycled into new star systems.
19
Q
What happens when we look farther into space?
A
We look further back in time, because light takes time to travel.
20
Q
How long does light take to reach us from the Sun?
A
About 8 minutes and 20s.
21
Q
How long does light take from Andromeda Galaxy?
A
About 2.5 million years
22
Q
How often does Earth rotate on its axis?
A
Once every day.
23
Q
How long is one orbit of Earth around the Sun?
A
One year (365.26 days).
24
Q
What is Earth’s average distance from the Sun?
A
1 AU = 150 million km.
25
What is the tilt of Earth’s axis?
23.5° (pointing toward Polaris).
26
Direction of Earth’s rotation and orbit?
it rotates west to east, and orbits counter clockwise
27
How fast does the Sun move relative to nearby stars?
~70,000 km/h (20 km/s)
28
How long does it take the Sun to orbit the Milky Way?
About 230 million years.
29
What is our Sun’s speed around the Milky Way?
~800,000 km/h.
30
What discovery confirmed the expanding universe?
Observations by Vesto Slipher, Carl Wirtz, Knut Lundmark, and Edwin Hubble (1917–1929).
31
What causes star trails in long-exposure photos?
Earth’s rotation relative to the stars.
32
What do stars appear to be projected onto from Earth’s perspective?
The celestial sphere.
33
Why do stars appear fixed even though they aren’t?
They are extremely far away and at vastly different distances.
34
What does the 23.5° tilt affect?
The apparent motion of the Sun, stars, and planets across the sky.
**It also is what causes the seasons**
35
Who has the oldest continuous astronomical tradition?
Indigenous Australian peoples, who have observed the sky for over 60,000 years.
36
What celestial features are important in Indigenous Australian astronomy?
The Emu in the Milky Way and the Southern Cross.
37
What are latitude and longitude used for in astronomy?
To determine what celestial events can be seen from your location.
38
What is the “False Southern Cross”?
A similar but misaligned star pattern that can mislead observers in the Southern Hemisphere.
39
What are the key points in Earth’s orbit marking seasonal changes?
The solstices and equinoxes.
40
What is Earthshine?
Faint illumination of the Moon’s dark side caused by sunlight reflected from Earth.
41
What is a lunar eclipse?
When Earth’s shadow falls on the Moon.
42
What are the types of solar eclipse?
Total, partial, and annular.
43
What is the Diamond Ring Effect?
A bright flash seen just before and after totality during a solar eclipse, along the edge of the moon where the sun peaks through
44
What is planetary alignment?
When several planets appear along a line in the sky.
45
What is retrograde motion?
The apparent backward motion of a planet relative to the background stars, due to Earth’s movement.
46
What is stellar parallax?
The apparent shift in position of nearby stars due to Earth’s orbit around the Sun.
47
What does parallax allow astronomers to measure?
The distances to nearby stars.
48
Why is parallax difficult to observe?
The effect is extremely small—about one-millionth of a meter at one meter (10⁻⁶ radians)—and decreases with distance.
49
What is scientific thinking based on?
Observation and trial-and-error experiments in everyday life.
50
How did astronomical observations benefit ancient societies?
They helped track time and seasons for agriculture, guided religious ceremonies, and aided navigation.
51
What astronomical achievements did ancient civilizations accomplish?
Tracking seasons and lunar cycles
Developing calendars
Monitoring planets and stars
Predicting eclipses
52
What device did ancient people use to tell time during daylight?
Sundials — shadows were used to mark the passage of time.
53
What is the Nebra Sky Disc and why is it significant?
A 3,600-year-old bronze disc from Germany — the oldest known depiction of astronomical phenomena, showing the Sun/Moon, Pleiades, and solstice angles.
54
How did the Aztecs use astronomy in their architecture?
The Templo Mayor was aligned so that the Sun rose between its twin temples at the equinoxes.
55
What is the Sun Dagger and what does it mark?
A solar marker at Fajada Butte (Chaco Canyon, New Mexico) that marks the summer solstice with sunlight patterns.
56
What supernova event did ancient astronomers record in 1054?
The Crab Nebula (SN 1054), observed by Chinese and possibly Pueblo astronomers.
57
How did Polynesians use astronomy?
For open-ocean navigation, using stars, ocean swells, and bird flight patterns.
58
Why does modern science trace its roots to the Greeks?
They were the first to create models of nature and sought rational (non-mythological) explanations for natural patterns.
59
Which earlier region influenced Greek science and math?
The Middle East — many Greek ideas built upon earlier Mesopotamian and Egyptian discoveries.
60
Who measured the Earth’s circumference around 240 BC, and how accurate was it?
Eratosthenes — his calculation was within about 5% of the modern value (~42,000 km).
61
What did Greek philosophers believe about celestial motion?
Planets and stars moved on perfect spheres or circles, and Earth was at the center (geocentric model).
62
Why was the geocentric model problematic?
It couldn’t naturally explain the apparent retrograde motion of planets.
63
Who created the Ptolemaic model, and what did it propose?
Claudius Ptolemy — planets moved on small circles (epicycles) whose centers moved around Earth on larger circles (deferents).
64
How long did the Ptolemaic model remain dominant?
About 1,500 years.
65
Who proposed the modern heliocentric model of the Solar System?
Nicolaus Copernicus (1473–1543).
66
What was the main limitation of Copernicus’s model?
It still used perfect circles, so it wasn’t more accurate than the Ptolemaic model.
67
Who made the most accurate naked-eye astronomical observations?
Tycho Brahe (1546–1601) — accurate to about one arcminute.
68
What was Tycho Brahe’s main conclusion?
The other planets orbit the Sun, but he believed Earth was stationary because he couldn’t detect stellar parallax.
69
Who used Tycho’s data to discover the true nature of planetary motion?
Johannes Kepler (1571–1630).
70
What did Kepler discover after noticing an 8-arcminute discrepancy in Mars’s orbit?
Planetary orbits are ellipses, not circles.
71
What is Kepler’s First Law (1609)?
Each planet’s orbit around the Sun is an ellipse, with the Sun at one focus.
72
What is Kepler’s Second Law (1609)?
A planet sweeps out equal areas in equal times as it orbits — meaning it **moves faster when closer to the Sun.**
73
What is Kepler’s Third Law (1619)?
The square of a planet’s orbital period (p²) is proportional to the cube of its average distance (a³).
👉
𝑝^2 = 𝑎^3
74
What does Kepler’s Third Law tell us about planetary speed?
More distant planets move slower on average.
75
What technological innovation did Galileo use for astronomy?
The telescope — he built his own to make detailed observations.
76
What did Galileo observe on the Moon?
Mountains and craters — showing it was not a perfect sphere.
77
What did Galileo observe around Jupiter?
Four moons orbiting Jupiter — evidence that not everything revolves around Earth.
78
How did Galileo’s observations of Venus support the heliocentric model?
The phases of Venus matched predictions of the Copernican (Sun-centered) model, not the geocentric one.
79
What were the three main Aristotelian objections to the Copernican view?
1. Earth could not be moving because objects in air would be left behind.
2. Non-circular orbits are not perfect. (The heavens are believed to be perfect)
3. No detectable stellar parallax.
80
How did Galileo refute the first objection (Earth could not be moving)?
He showed that objects in air move with Earth; objects stay in motion unless acted on by a force (Newton’s first law).
81
How did Galileo refute the second objection (heavenly perfection)?
He observed sunspots and mountains on the Moon, proving that the heavens were not perfect spheres.
82
How did Galileo refute the third objection (lack of parallax)?
He showed stars were much farther away than Tycho thought, so parallax was too small to detect with the naked eye.
83
What was Galileo’s overall contribution to the Copernican Revolution?
He overcame the remaining objections to the heliocentric model using observations and experiments.
84
Who explained Kepler’s laws using physics?
Sir Isaac Newton (1642–1727).
85
What was Newton’s major realization about physical laws?
The same laws of physics apply both on Earth and in the heavens.
86
State Newton’s Law of Universal Gravitation.
1. Every mass attracts every other mass.
2. Attraction ∝ product of masses.
3. Attraction ∝ 1 / (distance²).
87
What are the consequences of Newton’s law of gravity?
1. Kepler’s first two laws apply to all orbiting objects.
2. Orbits can be bound (ellipses) or unbound (parabolas/hyperbolas).
88
What is energy?
The ability to do work; the ‘currency of nature’. It enables all activity and requires replenishment (e.g., food for humans).
89
What are the SI and common units of energy?
Joule (J) and electron Volt (eV). 1 eV = 1.6×10⁻¹⁹ J. 1 Cal = 1 kcal = 4.184 kJ.
90
Give examples of everyday energy values.
• 1-ton car at 100 km/h → 386 kJ
• Daily human food intake → ~10,500 kJ
• Photon in sunlight → ~2 eV
91
What is power?
Energy used or produced per unit time. Unit: Watt (W) = 1 J/s.
92
What is the Sun’s power at Earth’s orbit?
1.37 kW/m² of electromagnetic radiation.
93
How do we experience light?
As both brightness and warmth. Light is a form of energy; its energy flow (power) is measured in Watts.
94
What does ‘1 Watt’ mean?
1 Joule per second (1 J/s) — the rate at which energy is delivered or used.
95
How can sunlight at Earth’s orbit meet human energy needs?
At 1.37 kW/m², about 3 m² of sunlight could meet one person’s power needs if fully converted.
96
What is white light?
White light is made up of many component colours (the visible spectrum).
97
How do light and matter interact?
- emission
- absorption
- transmission
- reflection
- scattering
98
What’s the difference between transparent and opaque objects?
Transparent objects transmit light; opaque objects absorb or block it.
99
What is reflection?
Light bouncing off a surface in a specific direction (e.g., a mirror).
100
What is scattering?
Light bouncing in many directions, allowing multiple observers to see it (e.g., a movie screen).
101
Why is a rose red?
Because it reflects red light and absorbs other colours.
102
What is light?
Light behaves as both a wave and a particle — a concept known as wave-particle duality.
103
What are photons?
Particles of light, each carrying energy that depends on its frequency.
104
What is a wave?
A pattern of motion that carries energy without transporting matter.
105
Define wavelength and frequency.
Wavelength: distance between peaks; Frequency: number of vibrations per second.
106
What is the relationship between wave speed, wavelength, and frequency?
Wave speed = wavelength × frequency.
107
What fields make up light waves?
Oscillating electric and magnetic fields (electromagnetic waves).
108
What is the speed of light?
3 × 10⁸ m/s.
109
What determines the energy of a photon?
Its frequency: E = h × f (Planck’s constant h = 6.626×10⁻³⁴ J·s).
110
How are wavelength, frequency, and energy related?
High frequency → high energy → short wavelength; Low frequency → low energy → long wavelength.
**the longer the wavelength, the lower the frequency and energy**
111
What is the electromagnetic spectrum?
The full range of light wavelengths — most of which are invisible to human eyes.
112
What is an atom?
The basic unit of matter consisting of a nucleus surrounded by electrons.
113
What makes up the nucleus of an atom?
Protons and neutrons.
114
What is an electron cloud?
The region around a nucleus where electrons are likely to be found.
115
What is the approximate size of an electron cloud?
About 10^-10 meters.
116
What is the approximate size of a nucleus?
About 10^-15 meters.
117
What is the atomic number?
The number of protons in the nucleus.
118
What is the atomic mass number?
The total number of protons and neutrons in the nucleus.
119
What is a molecule?
A group of two or more atoms bonded together (e.g., H2O, CO2).
120
What is an isotope?
Atoms with the same number of protons but different numbers of neutrons.
121
What are the four main phases of matter?
Solid, liquid, gas, and plasma.
122
What is plasma?
A phase where atoms are broken into ions and electrons.
123
What causes phase changes?
Increasing temperature, which breaks chemical and physical bonds.
124
What is ionization?
The process of stripping electrons from atoms, forming plasma.
125
What is dissociation?
The breaking of molecules into atoms.
126
What is evaporation?
The process that changes liquid into gas by breaking flexible bonds.
127
What is melting?
The process that changes solid into liquid by breaking rigid bonds.
128
What two factors determine a substance’s phase?
Temperature and pressure.
129
How is energy stored in atoms?
In specific, quantized energy levels of electrons.
130
What kind of transitions between energy levels are allowed?
Only specific quantum transitions; arbitrary ones are forbidden.
131
What are the three basic types of spectra?
Continuous, emission line, and absorption line spectra.
132
What produces a continuous spectrum?
Dense materials such as solids or dense gases.
133
What produces an emission line spectrum?
Thin or low-density gases emitting light at specific wavelengths.
134
What produces an absorption line spectrum?
A thin gas absorbing specific wavelengths from background light.
135
What does each atom have that makes it identifiable in a spectrum?
A unique set of energy levels or spectral fingerprints.
136
What do downward transitions in atoms produce?
Emission lines.
137
What do upward transitions in atoms produce?
Absorption lines.
138
What extra energy levels do molecules have?
Vibrational and rotational energy levels.
139
Why are molecular spectra complex?
Because of the large number of vibrational and rotational transitions.
140
In what part of the spectrum are many molecular transitions found?
In the infrared region.
141
What is thermal radiation?
Radiation emitted by all dense objects based on their temperature.
142
What does the thermal radiation spectrum depend on?
Only the object’s temperature.
143
How does the intensity of emitted light change with temperature?
Hotter objects emit more light at all frequencies.
144
How does the color of emitted light change with temperature?
Hotter objects emit shorter wavelength (bluer) light.
145
Which type of star is hotter, blue or red?
A blue star.
146
What can we learn from studying a spectrum?
We can determine composition, temperature, and physical properties of an object.
147
What does a reflected sunlight spectrum with less blue light indicate?
The object appears red.
148
What does an infrared spectrum peaking at 225 K indicate?
Thermal radiation from a cool object like Mars.
149
What molecule causes absorption lines of CO2 in a spectrum?
Carbon dioxide.
150
What do ultraviolet emission lines indicate?
A hot upper atmosphere.
151
What planet’s spectrum shows these combined features?
Mars.
152
What is the Doppler effect?
The change in wavelength of light due to motion of the source toward or away from the observer.
153
What does a redshift indicate?
The object is moving away from the observer.
154
What does a blueshift indicate?
The object is moving toward the observer.
155
What do we measure to determine Doppler shift?
Shifts in the wavelengths of spectral lines.
156
If a star's spectral line shifts from 500.7 nm to 502.8 nm, what does this indicate?
The star is moving away from us (redshift).
157
What is Doppler broadening?
The widening of spectral lines caused by rotation or motion within an object.
158
How can Doppler broadening indicate rotation?
Faster rotation causes wider spectral lines.
159
What part of an object moving toward us causes a blueshift?
The side rotating toward the observer.
160
What part of an object moving away causes a redshift?
The side rotating away from the observer.
161
What is refraction?
The bending of light as it passes from one substance to another.
162
How does your eye focus light?
By using refraction to bend light so it converges on the retina.
163
What is the focal plane?
The surface where light from different directions comes into focus.
164
Is the image formed by a single convex lens upright or inverted?
Inverted (upside down).
165
How do cameras record images?
They use lenses to focus light and CCD detectors to capture it.
166
What is a CCD?
A charge-coupled device used to detect light in cameras and telescopes.
167
How are CCDs in telescopes similar to those in digital cameras?
Both detect light electronically to form digital images.
168
What are the two most important properties of a telescope?
Light-collecting area and angular resolution.
169
What does light-collecting area determine?
How much light a telescope can gather in a given time.
170
How is a telescope’s light-collecting area related to its diameter?
Area = π × (diameter / 2)².
171
What is angular resolution?
The smallest angular separation that a telescope can distinguish.
172
What is the diffraction limit?
The limit on angular resolution caused by interference of light waves.
173
What improves angular resolution?
Larger telescope diameter (larger light collection area).
174
What are the two basic types of optical telescopes?
Refracting and reflecting telescopes.
175
What do refracting telescopes use to focus light?
Lenses.
176
What do reflecting telescopes use to focus light?
Mirrors.
177
Why are refracting telescopes less common today?
They require long tubes and heavy glass lenses.
178
Why are reflecting telescopes preferred?
They can have much larger diameters and are easier to build.
179
Where are the twin Keck telescopes located?
Mauna Kea, Hawaii.
180
How large are the mirrors of the Keck telescopes?
10 meters in diameter.
181
What is the Extremely Large Telescope (ELT)?
A new telescope under construction by the ESO with a massive segmented mirror.
182
When is the ELT expected to achieve first light?
March 2029.
183
What are the three main things astronomers do with telescopes?
Imaging, spectroscopy, and timing.
184
What is imaging in astronomy?
Taking pictures of astronomical objects like planets, stars, and galaxies.
185
What is spectroscopy?
Breaking light into spectra to analyze emission or absorption features.
186
What is timing in astronomy?
Measuring how light output or radiation changes with time.
187
Why do astronomical detectors need multiple images for color?
(They take one pic in yellow, then red, then blue (for example))
They record only one color of light at a time.
188
What do X-ray images often use to represent data?
Colors that represent different energies of non-visible light.
189
What does a spectrograph do?
Separates different wavelengths of light before they hit the detector.
190
What is a light curve?
A graph showing how brightness changes over time.
191
Who was Vera Rubin?
An astronomer who found evidence for dark matter.
192
What is special about the Vera C. Rubin Observatory?
It has the world's largest digital camera with 3.2 gigapixels.
193
What are the two main telescope properties?
Collecting area and angular resolution.
194
What are the two basic telescope designs?
Refracting (lenses) and reflecting (mirrors).
195
Why are most professional telescopes reflectors?
They can be built larger and with fewer optical distortions.
196
What are the three main uses of telescopes?
Imaging, spectroscopy, and timing.
197
What causes light pollution?
Scattering of human-made light in the atmosphere.
198
Why are Starlink satellites a problem for astronomy?
They cause bright streaks and noise in telescope images.
199
What are the best conditions for observing?
Calm, high, dark, and dry locations.
200
Why are the best observatories built on mountains?
Thin, dry air and reduced atmospheric distortion improve viewing.
201
Which wavelengths pass easily through Earth's atmosphere?
Radio and visible light.
202
Why do we put telescopes in space?
To observe wavelengths blocked by Earth's atmosphere.
203
Where is the James Webb Space Telescope located?
1.5 million kilometers from Earth at the L2 point.
204
Does the JWST orbit Earth?
No, it moves with Earth around the Sun.
205
What temperature is JWST’s camera kept at?
Around -100°C.
206
What is a radio telescope?
A large dish that reflects radio waves to a focus.
207
How large is the FAST radio telescope?
500 meters in diameter.
208
What kind of light does a standard satellite dish collect?
Radio waves.
209
Why do infrared and ultraviolet telescopes need to be above the atmosphere?
Because the earths atmosphere blocks them
210
Where was the SOFIA infrared telescope mounted?
In a Boeing 747 aircraft.
211
Why must X-ray telescopes be in space?
Earth’s atmosphere blocks X-rays.
212
Why must gamma-ray telescopes be in space?
High-energy gamma rays are blocked by the atmosphere.
213
Why is focusing gamma rays difficult?
They are very energetic and rare.
214
How are gamma rays detected?
Through electron-positron pair creation in tungsten foils.
215
What is a telescope array?
A system combining signals from multiple telescopes to act as one large one.
216
Where are the SKA telescopes located?
South Africa (mid-frequency) and Australia (low-frequency).
217
What does the H.E.S.S. array detect?
Gamma rays with energies between 30 GeV and 100 TeV.
218
How do Air Cherenkov Telescopes detect high-energy gamma rays?
By observing Cherenkov radiation from particles created in the atmosphere.
219
What types of light can be observed from the ground?
Visible light and radio waves.
220
What is the largest optical telescope size currently in use?
About 10 meters in diameter.
221
What is the largest radio telescope?
The FAST telescope with a 500-meter diameter.
222
What powers the Sun?
Nuclear fusion converting hydrogen into helium.
223
What was the incorrect early theory of the Sun’s power source?
Chemical burning.
224
Why can’t chemical energy power the Sun?
It would only last about 10,000 years.
225
What is gravitational contraction?
Energy released by the slow contraction of the Sun as it formed.
226
What stopped the Sun’s contraction?
Nuclear fusion began, balancing gravity.
227
What is gravitational equilibrium?
Balance between outward pressure from fusion and inward pull of gravity.
228
What equation describes the Sun’s energy from fusion?
E = mc².
229
What type of nuclear reaction powers stars?
Fusion.
230
What is nuclear fission?
Splitting large nuclei into smaller ones (used in power plants).
231
What is nuclear fusion?
Combining small nuclei to form a larger one (powers stars).
232
What enables fusion in the Sun’s core?
High temperature and pressure.
233
What does the Sun fuse in its core?
Four hydrogen nuclei into one helium nucleus.
234
What are the byproducts of hydrogen fusion?
Helium, gamma rays, positrons, and neutrinos.
235
How much mass is lost in the fusion process?
About 0.7% of the mass is converted to energy.
236
What is luminosity?
The total power a star radiates, measured in watts.
237
What is apparent brightness?
The amount of starlight that reaches Earth per square meter.
238
What is the formula relating brightness and luminosity?
Brightness = Luminosity / (4π × distance²).
239
How can luminosity be determined?
By measuring a star’s distance and apparent brightness.
240
What is parallax?
The apparent shift in a star’s position due to Earth’s motion around the Sun.
241
How is distance in parsecs calculated?
d (parsecs) = 1 / p (arcseconds).
242
How is distance in light-years calculated?
d (ly) = 3.262 / p (arcseconds).
243
What are the most and least luminous stars?
Most: 10⁶ L☉, Least: 10⁻⁴ L☉.
244
What is the Sun’s luminosity symbol?
L☉ (L-sun).
245
What determines a star’s temperature?
Its thermal radiation spectrum.
246
What is the temperature range of stars?
From about 3,000 K to 50,000 K.
247
What is the Sun’s surface temperature?
About 6,000 K.
248
What do absorption lines in a spectrum show?
The ionization level and temperature of the star.
249
What does a star’s spectral type indicate?
Its temperature and composition.
250
What are the spectral types from hottest to coolest?
O, B, A, F, G, K, M.
251
What pnumoics helps remember spectral types?
Oh, Be A Fine Girl/Guy, Kiss Me.
252
How are stellar masses measured?
Using gravity and Kepler’s third law in binary star systems.
253
What is a visual binary?
Two stars visible separately that orbit each other.
254
What is a spectroscopic binary?
A system where Doppler shifts reveal the orbital motion.
**We determine the orbit by measuring doppler shift**
255
What is an eclipsing binary?
A system where one star passes in front of the other, dimming the light.
256
What fraction of stars are in binary systems?
About half.
257
What is the mass range of stars?
From 0.08 M☉ to about 150 M☉ (possibly 300 M☉).
258
What is M☉?
The mass of the Sun.
Fall 2025
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