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A Beginner’s Guide to the Universe

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1 A Beginner’s Guide to the Universe
Lecture Outlines Introduction Astronomy: A Beginner’s Guide to the Universe 5th Edition Chaisson / McMillan © 2007 Pearson Prentice Hall This work is protected by United States copyright laws and is provided solely for the use of instructors in teaching their courses and assessing student learning. Dissemination or sale of any part of this work (including on the World Wide Web) will destroy the integrity of the work and is not permitted. The work and materials from it should never be made available to students except by instructors using the accompanying text in their classes. All recipients of this work are expected to abide by these restrictions and to honor the intended pedagogical purposes and the needs of other instructors who rely on these materials.

2 Introduction Exploring the Heavens

3 Units of the Introduction
The “Obvious” View Earth’s Orbital Motion The Motion of the Moon The Measurement of Distance Scientific Theory and the Scientific Method

4 What is Astronomy and how do we use the celestial sphere to study space?

5 What is Astronomy? Astronomy: study of the universe Universe
Totality of all space, time, matter and energy Solar system, stars, galaxies, astrobiology, etc Actual science (physical) observations, data, facts

6 What is Astronomy? Astrology: study of the movements and relative positions of celestial bodies and their supposed influence on human affairs horoscopes, lunatics….

E.1 The “Obvious” View Earth is average – we don’t occupy any special place in the universe Scales are very large: measure in light-years, the distance light travels in a year – about 10 trillion miles THE BIGGEST STARS IN THE UNIVERSE VIDEO

8 Celestial Sphere Ancients used to think stars moved around Earth
Stars’ apparent motion is due to Earth’s rotation on axis Axis intersection points: -North Celestial Pole -South Celestial Pole -Midway = Celestial Equator

9 Celestial Sphere -Stars seem to be on the inner surface of a sphere surrounding the Earth -They aren’t!! -Use two-dimensional spherical coordinates (similar to latitude and longitude) to locate sky objects

10 E.1 Celestial Coordinates
Declination: degrees north or south of celestial equator (similar to latitude) Celestial Equator = 0° (0-90) Above CE = +X°; below CE = -X°

11 E.1 Celestial Coordinates
Right ascension (RA): measured in hours, minutes, and seconds eastward from position of Sun at vernal equinox (similar to longitude; east-west)

12 E.1 Celestial Coordinates
Right ascension: Starting Line (0) = line from North star to Sun on the vernal equinox (March 21) Maximum RA= 24 hrs

13 How does the Earth’s orbital motion cause changes on Earth?

14 Revolution vs. Rotation
Revolution: time it takes to orbit around an object EXAMPLE Earth year: 365 ¼ days around the sun (counterclockwise) Moon: ~27 1/3 days around Earth (cc)

15 Revolution vs. Rotation
Rotation: time it takes to complete a turn on its own axis EXAMPLE Earth day: 24 hours (counterclockwise) Moon: ~27 1/3 days (cc)

16 Synchronous Rotation Rotation time = Revolution time
Always see same side of the moon!

17 E.2 Earth’s Orbital Motion
Solar day- Daily cycle, noon to noon, is diurnal motion 24 hours Sidereal day – Time it takes the stars to be in the exact same location 23 hrs 56 min “sidus”= star

18 E.2 Earth’s Orbital Motion
Ecliptic is plane of Earth’s path around Sun at 23.5° to celestial equator

19 E.2 Earth’s Orbital Motion
Northernmost point (above celestial equator) is summer solstice Southernmost is winter solstice Points where path cross celestial equator are vernal and autumnal equinoxes

20 E.2 Earth’s Orbital Motion


22 E.2 Earth’s Orbital Motion
Summer solstice longest amount of daylight of year usually June 21 first day of summer Winter solstice shortest amount of daylight of year usually Dec. 21 or 22 first day of winter

23 E.2 Earth’s Orbital Motion
Vernal equinox equal amount of daylight and dark usually March 20 or 21 first day of spring Autumnal equinox usually Sept first day of fall

24 E.2 Earth’s Orbital Motion
Seasons are caused by: Combination of day length and sunlight angle due to axis TILT Not distance from sun Perihelion- January 3 Aphelion- July 4

25 E.2 Earth’s Orbital Motion
Tropical year (Our calendar) Time from one vernal equinox to the next Follows seasons Sidereal year Time for Earth to orbit once around Sun, relative to fixed stars Follows constellations In 13,000 years July and August will still be summer, but Orion will be a summer constellation

26 Watch the changing seasons
Notice it is harder to tell in Southern Hemi. Because not as much land

27 E.2 Earth’s Orbital Motion
Precession: rotation of Earth’s axis itself; makes one complete circle in about 26,000 years (like a top)

28 Essential Question How does the motion of the moon cause us to see different phases and different types of eclipses? animated GIF created by Antonio Cidadao


30 E.3 Motion of the Moon Half of moon’s surface is ALWAYS illuminated by the sun!!! Wax-grow Right edge Wane-shrink Left edge

31 Lunar Phases Motion of the Moon
animated GIF created by Antonio Cidadao

32 E.3 Motion of the Moon Synodic month
29.5 days to go through whole cycle of phases Phases -different amounts of sunlit portion being visible from Earth Sidereal month Time to make full 360° around Earth (orbital time) 27.3 days

33 Moon Features Natural Satellite Gravity causes tides Maria
Most obvious darkened areas Craters Circular, bowl shaped holes Formed by impacts long ago No erosion forces Atmosphere, water, wind

34 Waxing crescent – 1st quarter – waxing gibbous
Lunar Phases Waxing crescent Waxing crescent – 1st quarter – waxing gibbous Waxing gibbous Full – waning gibbous Waning gibbous – waning crescent Waning crescent-new moon Photo from:

35 Motion of the Moon Eclipse:
When the sun or moon is blocked to an observer on Earth for a short period of time (minutes or hours) Caused by shadows of Earth or Moon Umbra- darkest part of the shadow Penumbra- lightest part of the shadow Lunar eclipse: Moon is blocked Solar eclipse: Sun is blocked

36 Motion of the Moon Lunar eclipse: Earth is between Moon and Sun
Only occurs during full moon phase

37 When the Earth’s shadow covers the Moon, we have a lunar eclipse


39 3 types of Lunar Eclipses
Penumbral Partial Total

40 3 types of Lunar Eclipses
Penumbral lunar eclipse the Moon only passes through the penumbra of Earth’s shadow

41 3 types of Lunar Eclipses
Partial lunar eclipse part of the Moon passes through the umbra of Earth’s shadow

42 3 types of Lunar Eclipses
Total lunar eclipse the entire Moon passes through the umbra of Earth’s shadow (turns red) Total Lunar Eclipes Time Lapse Video *Next Total Lunar Eclipse not until April 15, 2014*

43 Why is the Moon red during an eclipse?
Atmosphere filters some sunlight and allows it to reach the Moon’s surface Blue light is removed Remaining light is red or orange Bent or refracted so that a small fraction of it reaches the Moon Exact appearance depends on dust and clouds in the Earth’s atmosphere

44 E.3 Motion of the Moon Solar eclipse: Moon is between Earth and Sun
New Moon 3 types Partial Total Annular


46 Solar Eclipse

47 E.3 Motion of the Moon Partial part of Sun is blocked
Seen by people located in the penumbral shadow

48 E.3 Motion of the Moon Total entire sun is blocked
Corona becomes visible Low density cloud of plasma with higher transparency than the inner layers “Diamond Ring” effect

49 “Diamond Ring” Effect Before Totality Begins
In the last seconds before totality begins, the remaining bit of Sun resembles a dazzling jewel as the ring-like corona appears.

50 Photo of a Total Solar Eclipse

51 Total Solar Eclipse from Antarctica
Credit: Fred Bruenjes It’s possible to see a total eclipse from anywhere on Earth. This image was shot in Antarctica in 2003.


53 E.3 Motion of the Moon Annular-
Moon is too far from Earth for total (umbra doesn’t reach surface of Earth) Forms a ring No corona visible photos taken by Fred Espenak

54 Annular Solar Eclipse

55 Solar Eclipse This is a photo taken from the former Soviet space station MIR. It shows the shadow of the Moon falling on the Earth in Anyone under the shadow saw a solar eclipse.

56 E.3 Motion of the Moon Eclipses don’t occur every month because Earth’s and Moon’s orbits are not in the same plane 5° tilt compared to ecliptic

57 E.3 Motion of the Moon Eclipse tracks,

58 Constellations and parallax
How do astronomers identify stars, name stars and calculate their distances?

59 Constellations Patterns of stars in the sky that’s “relative” distance doesn’t change Most visible in Northern Hemisphere named after mythological heroes and animals by Greek astrologers Different constellations visible at night during different times of year; appear to move from east to west during night 88 total constellations Still used to specify large areas of the sky

60 Locating a star Easiest way: specify constellation then rank in order of brightness using Greek alphabet Alpha (α)- Brightest star Beta (β)- Second brightest Method can only be used with naked eye since limited number of letters

61 The “Obvious” View Stars that appear close in the sky may not actually be close in space:

62 Earth’s Orbital Motion
12 constellations Sun moves through during the year are called the zodiac

63 The Measurement of Distance
Triangulation: measure baseline and angles, can calculate distance

64 The Measurement of Distance

65 The Measurement of Distance
Parallax: similar to triangulation, but look at apparent motion of object against distant background from two vantage points Larger parallax= closer the object Smaller parallax= farther the object


67 Measuring with Parallax
Ruler, tape, cardboard, scissors Cut out both pieces along dashed line Fold up arrows on dotted lines Stick pushpin through both pieces and cardboard Select a colored target Make a perpendicular baseline taping ruler to desk

68 Measuring with Parallax
Put EYE ARROW on one end of baseline Line up EYE ARROW, REFERENCE ARROW and REFERENCE POINT (corner)-gunsight Pivot TARGET ARROW until it is aligned with EYE ARROW and TARGET OBJECT (scale piece should NOT move, only the pointer) Read “Angle to Target object” and put on worksheet as “Target Angle 1” Repeat previous steps from opposite side of the baseline and write down Angle in “Target angle 2” Complete calculations (Baseline=30 cm)

69 Scientific Theory and the Scientific Method
What is a Scientific theory and how is it developed?

70 Scientific Theory and the Scientific Method
Scientific theories: must be testable must be continually tested should be simple should be elegant Scientific theories can be proven wrong, but they can never be proven right with 100% certainty

71 Scientific Theory and the Scientific Methods
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.

72 Summary of the Introduction
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

73 Summary of the Introduction
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, …

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