chapter 0 charting the heavens
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Chapter 0 Charting the Heavens. Charting The Heavens. 0.1 The “Obvious” View . Earth is average – we don’t occupy any special place in the universe Universe: Totality of all space, time, matter, and energy Astronomy: Study of the universe - PowerPoint PPT PresentationTRANSCRIPT
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Chapter 0Charting the
Heavens
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Charting The Heavens
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• Earth is average – we don’t occupy any special place in the universe
• Universe: Totality of all space, time, matter, and energy
• Astronomy: Study of the universe• Scales are very large, measured in
light-years, the distance light travels in a year – about 10 trillion miles
0.1 The “Obvious” View
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Figure 0.2
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Stars that appear close in the sky may not actually be close in space.
0.1 The “Obvious” View
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Stars in a constellation are
Question 1
a) physically close to each other.b) usually equal in brightness.c) about the same age.d) about the same distance away.e) in the same part of the sky.
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Question 1
a) physically close to each other.b) usually equal in brightness.c) about the same age.d) about the same distance away.e) in the same part of the sky.
Stars in a constellation are
Stars within a constellation might be very different distances, ages, types,
and brightness.
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a) the Earth orbits the Sun.b) the Moon orbits the Earth.c) stars are in constant motion.d) the Sun orbits the Earth.e) the Earth spins on its axis.
Question 2
Constellations appear to move across the sky at night because
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Question 1
1) the motion of Earth around the Sun2) the motion of the Moon around Earth3) the motion of Mars around the Sun4) the motion of the constellations around
Earth5) the spinning of Earth on its axis
What motion is responsible for the apparent motion of the constellations (east to west) across the sky?
a) the Earth orbits the Sun.b) the Moon orbits the Earth.c) stars are in constant motion.d) the Sun orbits the Earth. e) the Earth spins on its axis.
Question 2
Constellations appear to move across the sky at night because
The Sun, Moon, planets, and stars all rise and set
because our planet rotates once each day.
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Figure 0.5
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The celestial sphere:• Stars seem to be on the
inner surface of a sphere surrounding the Earth.
• They aren’t, but we can use two-dimensional spherical coordinates (similar to latitude and longitude) to locate sky objects.
0.1 The “Obvious” View
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• Full circle contains 360° (degrees).
• Each degree contains 60′ (arc-minutes).
• Each arc-minute contains 60″ (arc-seconds).
• Angular size of an object depends on actual size and distance away.
More Precisely 0-1: Angular Measure
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• Declination: Degrees north or south of celestial equator
• Right ascension: Measured in hours, minutes, and seconds eastward from position of the Sun at vernal equinox
0.1 The “Obvious” View
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Time for Earth to orbit once around the Sun, relative to fixed stars, is sidereal year.
Tropical year follows seasons; sidereal year follows constellations – in 13,000 years July and August will still be summer, but Orion will be a summer constellation.
0.2 Earth’s Orbital Motion
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• Daily cycle, noon to noon, is diurnal motion – solar day.
• Stars aren’t in quite the same place 24 hours later, though, due to Earth’s rotation around the Sun; when they are in the same place again, one sidereal day has passed.
0.2 Earth’s Orbital Motion
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Question 3What is the path that the Sun, Moon, and planets follow through the constellations?
a) the celestial equatorb) the north celestial polec) the Milky Wayd) the zodiace) the ecliptic
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a) the celestial equatorb) the north celestial polec) the Milky Wayd) the zodiace) the ecliptic
Question 3What is the path that the Sun, Moon, and planets follow through the constellations?
The ecliptic also marks the plane of
Earth’s orbit around the Sun.
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How long does it take the Sun to complete one circuit of the ecliptic?
Question 4
a) one hourb) one dayc) one monthd) one yeare) one decade
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1) one hour2) one day3) one month4) one year5) one decade
How long does it take the Sun to complete one circuit of the ecliptic?
Question 4
The Sun moves around the ecliptic once as the Earth orbits in one year.
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The 12 constellations the Sun moves through during the year are called the zodiac; path is ecliptic.
0.2 Earth’s Orbital Motion
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a) Wobble of Earth’s rotation axis b) the greenhouse effectc) 23.5° tilt of Earth’s rotational axisd) movement of Earth closer to or
farther from the Sune) global warming and cooling
What causes Earth’s seasons?
Question 5
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a) Wobble of Earth’s rotation axis b) the greenhouse effectc) 23.5° tilt of Earth’s rotational axisd) movement of Earth closer to or
farther from the Sune) global warming and cooling
What causes Earth’s seasons?
Question 5
Our planet’s tilt, and not its changing
distance from the Sun, creates seasons.
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• Ecliptic is plane of Earth’s path around the Sun; at 23.5° to celestial equator.
• Northernmost point (above celestial equator) is summer solstice; southernmost is winter solstice; points where path crosses celestial equator are vernal and autumnal equinoxes.
• Combination of day length and sunlight angle gives seasons.
• Time from one vernal equinox to next is tropical year.
0.2 Earth’s Orbital Motion
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Question 6
a) summer.b) fall.c) winter.d) spring.
The vernal equinox marks the beginning of
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Question 6
a) summer.b) fall.c) winter.d) spring.
The vernal equinox marks the beginning of
The vernal equinox occurs around March 21–22.
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a) every month at new moon.b) every week at the quarter phases.c) every month at full moon.d) about every six months at new moon.e) every year at new moon.
A solar eclipse happens
Question 7
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a) every month at new moon.b) every week at the quarter phases.c) every month at full moon.d) about every six months at new moon.e) every year at new moon.
Question 7
A solar eclipse happens
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Precession: Rotation of Earth’s axis itself; makes one complete circle in about 26,000 years
0.2 Earth’s Orbital Motion
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a) the rotation of Earth’s molten core. b) the gravitational pull of the Sun.c) the gravitational pull of the Moon. d) the weight of the ice at the poles.e) gravitational attractions from comets.
Precession is caused by
Question 8
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a) the rotation of Earth’s molten core. b) the gravitational pull of the Sun. c) the gravitational pull of the Moon. d) the weight of the ice at the poles.e) gravitational attractions from comets.
Precession is caused by
Question 8
The Moon’s tug creates a slow “wobble” that takes
26,000 years for one rotation.
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a) one dayb) one hourc) one weekd) one monthe) one year
Question 9
How long does it take the Moon to go around the ecliptic?
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a) one dayb) one hourc) one weekd) one monthe) one year
Question 9
How long does it take the Moon to go around the ecliptic?
The Moon orbits Earth in a month, and passes in front of the constellations of the zodiac, which are arranged around the ecliptic.
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The Moon takes about 29.5 days to go through whole cycle of phases – synodic month.Phases are due to different amounts of sunlit portion being visible from Earth.Time to make full 360° around Earth, sidereal month, is about 2 days shorter than synodic month.
0.3 The Motion of the Moon
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a) during the new moon phase.b) when the Sun blocks the Moon.c) during the full moon phase.d) always around the summer
solstice.
A total lunar eclipse occurs
Question 10
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a) during the new moon phase.b) when the Sun blocks the Moon.c) during the full moon phase.d) always around the summer
solstice.
A total lunar eclipse occurs
Question 10
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Lunar eclipse: • Earth is between the Moon and Sun • Partial when only part of the Moon is in
shadow• Total when all is in shadow
0.3 The Motion of the Moon
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Solar eclipse: the Moon is between Earth and Sun
0.3 The Motion of the Moon
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0.3 The Motion of the MoonSolar eclipse is partial when only part of the Sun is blocked, total when all is blocked, and annular when the Moon is too far from Earth for total.
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a) every month at new moon.b) every week at the quarter phases.c) every month at full moon.d) about every six months at new moon.e) every year at new moon.
A solar eclipse happens
Question 11
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a) every month at new moon.b) every week at the quarter phases.c) every month at full moon.d) about every six months at new moon.e) every year at new moon.
Question 11
A solar eclipse happens
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Eclipses don’t occur every month because Earth’s and the Moon’s orbits are not in the same plane.
0.3 The Motion of the Moon
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0.3 The Motion of the MoonEclipse tracks, 2010 - 2030
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a) the same phase in 24 hours. b) different phases in 24 hours.c) a lunar eclipse once a month.d) different sides of the Moon.
Considering the Moon’s phases, everyone on Earth sees
Question 12
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a) the same phase in 24 hours. b) different phases in 24 hours.c) a lunar eclipse once a month.d) different sides of the Moon.
Considering the Moon’s phases, everyone on Earth sees
Question 12
The Moon goes through its cycle of phases in about 30
days; the Earth rotates once in only 24 hours.
So everyone has a chance to see the same phase!
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Triangulation: Measure baseline and angles, and you can calculate distance.
0.4 The Measurement of Distance
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Parallax: Similar to triangulation, but looking at apparent motion of object against distant background from two vantage points
0.4 The Measurement of Distance
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Figure 0.21
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The angle of parallax increases as
Question 13
a) distances to stars increase.b) the baseline gets larger. c) the baseline gets smaller.d) the Earth moves faster in its orbit.
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a) distances to stars increase.b) the baseline gets larger. c) the baseline gets smaller.d) the Earth moves faster in its orbit.
The angle of parallax increases as
Question 13
The greater the distance between two observation points (the baseline), the
larger the angle of parallax.
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Scientific theories:• Must be testable• Must be continually tested• Should be simple• Should be elegantScientific theories can be proven wrong, but they can never be proven right with 100% certainty.
0.5 Science and the Scientific Method
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• Observation leads to theory explaining it.• Theory leads to predictions consistent with previous
observations.• Predictions of new
phenomena are observed. If the observations agree with the prediction, more predictions can be made. If not, a new theory can be made.
0.5 Science and the Scientific Method
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• Astronomy: Study of the universe• Stars can be imagined to be on inside of
celestial sphere; useful for describing location.• Plane of Earth’s orbit around Sun is ecliptic; at
23.5° to celestial equator.• Angle of Earth’s axis causes seasons.• Moon shines by reflected light, has phases.• Solar day ≠ sidereal day, due to Earth’s rotation
around Sun.
Summary of Chapter 0
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• Synodic month ≠ sidereal month, also due to Earth’s rotation around Sun
• Tropical year ≠ sidereal year, due to precession of Earth’s axis
• Distances can be measured through triangulation and parallax.
• Eclipses of Sun and Moon occur due to alignment; only occur occasionally as orbits are not in same plane.
• Scientific method: Observation, theory, prediction, observation …
Summary of Chapter 0, cont.