Chapter 2 - Spaceship Earth PDF

Spaceship Earth Our goals for learning: – How is Earth moving through space? – How do galaxies move within the universe?  How is Earth moving through space? Contrary to our perception, we are not "sitting still." We are moving with Earth in several ways, a...

Spaceship Earth Our goals for learning: – How is Earth moving through space? – How do galaxies move within the universe?  How is Earth moving through space? Contrary to our perception, we are not "sitting still." We are moving with Earth in several ways, and at surprisingly fast speeds. The Earth rotates around its axis once every day. © 2014 Pearson Education, Inc.  How is Earth moving through space? Earth orbits the Sun (revolves) once every year: – at an average distance of 1 AU ≈ 150 million kilometers. – with Earth's axis tilted by 23.5º (pointing to Polaris) It rotates in the same direction it orbits, counterclockwise as viewed from above the North Pole. © 2014 Pearson Education, Inc.  How is our Sun moving in in the Milky Way Galaxy? Our Sun moves randomly relative to the other stars in the local solar neighborhood… – typical relative speeds of more than 70,000 km/hr – but stars are so far away that we cannot easily notice their motion … and orbits the galaxy every 230 million years. © 2014 Pearson Education, Inc.  How is our Sun moving in in the Milky Way Galaxy? More detailed study of the Milky Way's rotation reveals one of the greatest mysteries in astronomy: © 2014 Pearson Education, Inc.  How do galaxies move within the universe? Galaxies are carried along with the expansion of the universe. But how did Hubble figure out that the universe is expanding? © 2014 Pearson Education, Inc.  Hubble discovered that All galaxies outside our Local Group are moving away from us. The more distant the galaxy, the faster it is racing away. Conclusion: We live in an expanding universe.  Are we ever sitting still? © 2014 Pearson Education, Inc.  What have we learned? How is Earth moving through space? – It rotates on its axis once a day and orbits the Sun at a distance of 1 AU = 150 million kilometers. – Stars in the Local Neighborhood move randomly relative to one another and orbit the center of the Milky Way in about 230 million years.  What have we learned? How do galaxies move within the universe? – All galaxies beyond the Local Group are moving away from us with expansion of the universe: the more distant they are, the faster they're moving.  The Human Adventure of Astronomy Our goals for learning: – How has the study of astronomy affected human history? How has the study of astronomy affected human history? The Copernican revolution showed that Earth was not the center of the Universe. Study of planetary motion led to Newton's laws of motion and gravity. Newton's laws laid the foundation of the industrial revolution. Modern discoveries are continuing to expand our "cosmic perspective."  Discovering the Universe for Yourself © 2014 Pearson Education, Inc.  Patterns in the Night Sky Our goals for learning: – What does the universe look like from Earth? – Why do stars rise and set? – Why do the constellations we see depend on latitude and time of year? © 2014 Pearson Education, Inc.  What does the universe look like from Earth? With the naked eye, we can see more than 2000 - stars as well as the Milky - Way. S - -The milky way > 3 : sort of band of clouds ps of gas and dust and other stars. depending upon Eights polition ( how we can see it ? getaway from from city lights. get far away , , go to dark spot. © 2014 Pearson Education, Inc.  ! Constellations Betelgense is the most likly star to explode in stars red in region it also - a part & your lifetime. oConstellation. A constellation is a region of the sky. - > - gi county lines. - There are eighty-eight (88) constellations in the entire sky. Winter tringle - closest brightest star ↳ in oursky. ↳ Slight years away. At winter. © 2014 Pearson Education, Inc.  Thought Question The brightest stars in a constellation A. all belong to the same star cluster. B. all lie at about the same distance from Earth. ⑨ C. may actually be quite far away from each other. © 2014 Pearson Education, Inc.  I s/ The Celestial Sphere sofficial The constellations cover the celestial Stars at different sphere distances all appear to lie on the celestial sphere. Some might appear close to each other and we group them in the same constellation. © 2014 Pearson Education, Inc.  We are in our planet Earth we & The Celestial Sphere on rotate on our axis we rotate , around the pole Ga Taxis - we are title actually as we are going around the sun we are tilted to that plane that we go around the Sun slibj the sun and degree > - equator by 23 The Ecliptic is the - Sun's apparent path through the celestial sphere. - the angle of O the Ecliptic - © 2014 Pearson Education, Inc.  The Celestial Sphere North celestial pole is directly above Earth's North Pole. South celestial pole is directly above Earth's South Pole. Celestial equator is a projection of Earth's equator onto sky. © 2014 Pearson Education, Inc.  The Milky Way A band of light making a circle around the celestial sphere. What is it? Our view into the plane of our galaxy. © 2014 Pearson Education, Inc.  The Milky Way we are about 30 , 000 light I6 years away from the central bulge. © 2014 Pearson Education, Inc.  The Local Sky An object's altitude (above horizon) and direction (along horizon) specify its location in your local sky. (directly overhead > - moving with me line from north to ↑ south that goes through the meridian. (right) > - moving with me © 2014 Pearson Education, Inc.  The Local Sky Meridian: line passing through zenith and connecting N and S points on horizon Zenith The · : point directly overhead. Horizon: all points Zenith: the point directly 90° away from zenith overhead © 2014 Pearson Education, Inc.  We measure the sky using angles. © 2014 Pearson Education, Inc.  Angular Measurements Full circle = 360º 1º = 60ʹ (arcminutes) 1ʹ = 60ʺ (arcseconds) geometrica ent Z Insert Figure 2.8 © 2014 Pearson Education, Inc.  Thought Question The angular size of your finger at arm's length is about 1°. How many arcseconds is this? A. 60 arcseconds B. 600 arcseconds O C. 60 × 60 = 3600 arcseconds © 2014 Pearson Education, Inc. Angular Size An object's angular size appears smaller if it is farther away. © 2014 Pearson Education, Inc. > - stars rise and set why ? Why do stars rise and set? , ↳ largely because our planet ↓apse photo is not because the spining , - stars are moving ↳ from 2-3 hours. J the pole Earth rotates from west to east, so stars appear to circle from east to west. © 2014 Pearson Education, Inc.  Our view from Earth: Stars near the north celestial pole are circumpolar and never set. We cannot see stars near the south celestial pole. All other stars (and Sun, Moon, planets) rise in east and set in west. you can't see the stars in this region. © 2014 Pearson Education, Inc.  Thought Question What is the arrow pointing to in the photo below? A. the zenith ⑨ B. the north celestial pole C. the celestial equator © 2014 Pearson Education, Inc.  Why do the constellations we see depend on latitude and time of year? They depend on latitude because your position on Earth determines which constellations remain below the horizon. They depend on time of year because Earth's orbit changes the apparent location of the Sun among the stars. © 2014 Pearson Education, Inc.  Review: Coordinates on the Earth GD Latitude: position north or south of equator -- Longitude: position east or west of prime sesibe meridian (runs through Greenwich, England) - sligt © 2014 Pearson Education, Inc. The sky varies with latitude but not with longitude. © 2014 Pearson Education, Inc.  Altitude of the celestial pole = your latitude Big bear little bear un bpole star © 2014 Pearson Education, Inc.  Thought Question The North Star (Polaris) is 50° above your horizon, due north. Where are you? A. You are on the equator. B. You are at the North Pole. ⑨ C. You are at latitude 50°N. D. You are at longitude 50°E. E. You are at latitude 50°N and longitude 50°E. © 2014 Pearson Education, Inc.  The sky varies as Earth orbits the Sun As the Earth orbits the Sun, the Sun appears to move eastward along the ecliptic. At midnight, the stars on our meridian are opposite the Sun in the sky. · E we go around the Sun as our planet Veles around the Sun. & The stars in the night sky will change because we are moving to see different parts of the sky © 2014 Pearson Education, Inc.  What have we learned? What does the universe look like from Earth? – We can see over 2000 stars and the Milky Way with our naked eyes, and each position on the sky belongs to one of 88 constellations. – We can specify the position of an object in the local sky by its altitude above the horizon and its direction along the horizon. Why do stars rise and set? – Because of Earth's rotation. © 2014 Pearson Education, Inc.  What have we learned? Why do the constellations we see depend on latitude and time of year? – Your location determines which constellations are hidden by Earth. – The time of year determines the location of the Sun on the celestial sphere. © 2014 Pearson Education, Inc.  The Reason for Seasons Our goals for learning: – What causes the seasons? – How does the orientation of Earth's axis change with time? © 2014 Pearson Education, Inc.  Thought Question TRUE OR FALSE? Earth is closer to the Sun in - = summer and farther from the Sun in winter. & Flase , distance Seasons cannot be are opposite in the N and S hemispheres the reason. , so & The real reason for seasons involves Earth's filt. (Mars Earth Saturn) axis -Like , , - - every planet have tilt : have seasons = ↳ planet does'n have tilt doesn't have every seasons i. & ↳Like (Jupiter Venus, © 2014 Pearson Education, Inc.  Why doesn't distance matter? jad Variation of Earth– - > for objects - variation in their with greater Earth-Sun Sun distance is small distance it can , play a large role in seasons Pluto is an example -. 3 20% or even more - —about 3%; this - not causing so much small variation is variation overwhelmed by the effects of axis tilt. Variation in any season of each hemisphere-Sun distance is even smaller! © 2014 Pearson Education, Inc.  What causes the seasons? Direct light causes more heating. © 2014 Pearson Education, Inc.  What causes the seasons? tilted 50 on 23. summer E ↑ inter Printer & T summer > - - june December = - : 98 Seasons depend on how Earth's axis affects the directness of sunlight. © 2014 Pearson Education, Inc. Axis tilt changes directness of sunlight during the year. When your hemisphere is pointing towards the Sun, it will be summer. When your hemisphere is pointing away from the Sun, it will be winter. have the - You length of day and night a exactly equal. "no matter where you are" to be. & "spring equinox" O "autumn equinox" © 2014 Pearson Education, Inc.  Sun's altitude also changes with seasons. Sun's position at noon in summer: Higher altitude F G summer higher it more means means more direct sunlight. sunlight more , warmer it means summer , Sun's position at Es winter noon in winter: Lower altitude means less direct sunlight. © 2014 Pearson Education, Inc.  Summary: The Real Reason for Seasons Earth's axis points in the same direction (to Polaris) all year round, so its orientation relative to the Sun changes as Earth orbits the Sun. Summer occurs in your hemisphere when = - sunlight hits it more directly; winter occurs when - - the sunlight is less direct. AXIS TILT is the key to the seasons; without it, we would not have seasons on Earth. © 2014 Pearson Education, Inc. How do we mark the progression of the seasons? We define four special points: &+54 summer (June) solstice & 15614 · winter (December) solstice 561615015 spring (March) equinox fall (September) equinox :$615414 © 2014 Pearson Education, Inc.  We can recognize solstices and equinoxes & by Sun's path across sky either fall or equinoxes. spring equinoxes. Summer (June) solstice: highest path; rise and set at most extreme north of due east Winter (December) solstice: lowest path; rise and set at most extreme south of due east Equinoxes: Sun rises precisely due east and sets precisely due west. 2 /j S S - - ↳ - · 2W. ·gspe 5 , ·I, 5555551j66. jus © 2014 Pearson Education, Inc. Seasonal changes are more extreme at high latitudes Path of the Sun on the summer solstice at the Arctic Circle © 2014 Pearson Education, Inc. How does the orientation of Earth's axis change with time? Although the axis seems fixed on human time - scales, it actually precesses over about 26,000 => years. - ⇒ Polaris won't always be the North Star. ⇒ Positions of equinoxes shift around orbit; e.g., spring equinox, once in Aries, is now in Pisces! - - Os - Earth's axis :, Ca 20051 precesses like -tword another star that the J051 the axis of a 7 reasons that the orientations - of seasons will change 54565 gi199 - - spinning top 5. bid i 15 (5j 4) 1997). · 255154 · = j5 1 155s"" ·j © 2014 Pearson Education, Inc.  What have we learned? What causes the seasons? – The tilt of the Earth's axis causes sunlight to hit different parts of the Earth more directly during the summer and less directly during the winter. – We can specify the position of an object in the local sky by its altitude above the horizon and its direction along the horizon. – The summer and winter solstices are when the Northern Hemisphere gets its most and least direct sunlight, respectively. The spring and fall equinoxes are when both hemispheres get equally direct sunlight. © 2014 Pearson Education, Inc.  What have we learned? How does the orientation of Earth's axis change with time? – The tilt remains about 23.5° (so the season pattern is not affected), but Earth has a 26,000 year precession cycle that slowly and subtly changes the orientation of Earth's axis. © 2014 Pearson Education, Inc.  The Moon, Our Constant Companion Our goals for learning: – Why do we see phases of the Moon? – What causes eclipses? © 2014 Pearson Education, Inc.  Why do we see phases of the Moon? 27 3. ·24j : 8192 Lunar phases are a > - the phase because of different angle of relected a a consequence of the sunlight with where respect to the observer. Moon's 27.3-day orbit around Earth. Mini © 2014 Pearson Education, Inc.  Phases of the Moon /1s , D ↳ did / ↑ this different phases of the moon and it's because Half of Moon is - relative to where we are on earth , what time we have , what part of month we are illuminated by Sun j J &S >Note - Emoon sun and is reflecting portion ofthe light that's how a we see it from the and half is dark. > - - - / 65519 We see a changing egg - combination of the counters bright and dark j - lockwise * faces as Moon &155big orbits. > - jjf), 50 Jogsd - - · hasspening when you have the moon on i the sun the opposite side compared to - % 09 [15 Sobserver © 2014 Pearson Education, Inc.  Phases of the Moon © 2014 Pearson Education, Inc.  Moon Rise/Set by Phase © 2014 Pearson Education, Inc.  Phases of the Moon: 29.5-day cycle Waxing Moon visible in afternoon/evening - - Gets "fuller" and rises later each day Waning Moon visible in late - night/morning -- Gets "less full" and sets later each day © 2014 Pearson Education, Inc.  Thought Question It's 9 a.m. You look up in the sky and see a moon with half its face bright and half dark. What phase is it? A. first quarter B. waxing gibbous C. third quarter D. half moon © 2014 Pearson Education, Inc. We only see one side We see only one side of Moon & of the moon we don't , reallysee the other side ↳ the names of it the you will see all of tislissie moons in russian because Synchronous rotation: the russions were the First people to send a spacecraft to study - what's behind the back of the moon , but we only see one side of it. the Moon rotates exactly once with each & because of it synchronous rotation. orbit. That is why only one side is visible from Earth. © 2014 Pearson Education, Inc.  -5) What causes eclipses? - The Earth and Moon cast shadows. When either passes through the other's shadow, we have an eclipse. 51jei Note "lunar eclipse S and the -if you the earth between the sun moon : have earth it's called "solar eclipse & if you see the shadow of the moon on : 15 3 it is related to 05 the orientation of moon , earth , and the Sun. ↳ if it is full - shadow "numbra" , if it is partially shadowed "penumbra". © 2014 Pearson Education, Inc. ·95155/17  Lunar Eclipse we are looking to the T shadow of the earth on the moon. - = © 2014 Pearson Education, Inc.  When can eclipses occur? Lunar eclipses can occur only at because moon on the side opposite full moon. - Lunar eclipses can = be penumbral, partial, or total. = - © 2014 Pearson Education, Inc.  Shadow of Solar Eclipse > - the moon on earth. b the moon is blocking the sunlight forms for a few minites of fewslands. © 2014 Pearson Education, Inc.  Solar Eclipse © 2014 Pearson Education, Inc.  When can eclipses occur? Solar eclipses can occur only at new moon. - Solar eclipses can be partial, total, or annular. - - - = = = © 2014 Pearson Education, Inc. Why don't we have an eclipse at every new and full moon? Sony , don we it. see month f every G 2 = - this angle I - between moon or bit and ecliptic - Plane & that cause to nothave a solar and lunar eclipse once every month. = path of the earth d I around - Sun the - The Moon's orbit is tilted 5°to ecliptic plane. = - So we have about two eclipse seasons each year, with a lunar eclipse at - new moon and solar eclipse at full moon. © 2014 Pearson Education, Inc. Summary: Two conditions must be met to have an eclipse: 1. It must be full moon (for a lunar eclipse) or new - - - moon (for a solar eclipse). - - AND & 2. The Moon must be at or near one of the two points in its orbit where it crosses the ecliptic 01e5115915 J 5 199 plane (its nodes). ↳ jopBois © 2014 Pearson Education, Inc.  Predicting Eclipses Eclipses recur with the 18-year, 11 1/3-day saros cycle, but type (e.g., partial, total) and location may vary. © 2014 Pearson Education, Inc.  What have we learned? Why do we see phases of the Moon? – Half the Moon is lit by the Sun; half is in shadow, and its appearance to us is determined by the relative positions of Sun, Moon, and Earth. What causes eclipses? – Lunar eclipse: Earth's shadow on the Moon – Solar eclipse: Moon's shadow on Earth – Tilt of Moon's orbit means eclipses occur during two periods each year. © 2014 Pearson Education, Inc.  The Ancient Mystery of the Planets Our goals for learning: – What was once so mysterious about planetary motion in our sky? – Why did the ancient Greeks reject the real explanation for planetary motion? © 2014 Pearson Education, Inc.  Planets Known in Ancient Times w Mercury – difficult to see; always close to Sun in sky Venus (above Mercury – very bright when visible; morning or evening "star" Mars (middle) – noticeably red Jupiter (top) – very bright Saturn Cabore Mars – moderately bright same bath ecliptic plane © 2014 Pearson Education, Inc. What was once so mysterious about planetary motion in our sky? Planets usually move slightly eastward from night to night relative to the stars. But sometimes they go westward relative to the stars for a few weeks: apparent retrograde motion. © 2014 Pearson Education, Inc.  pd5131 & We see apparent retrograde motion when we pass by a planet in its orbit. © 2014 Pearson Education, Inc.  Explaining Apparent Retrograde Motion Easy for us to explain: occurs when we "lap" another planet (or when Mercury or Venus laps us). But very difficult to explain if you think that Earth is the center of the universe! In fact, ancients considered but rejected the correct explanation. © 2014 Pearson Education, Inc.  Why did the ancient Greeks reject the real explanation for planetary motion? El 11991 1559199 sitley e issis · Their inability to ·g b observe stellar i : parallax was a major factor. Parallax Interactive Animations Stars in the Earth-Sun plane: http://www.kcvs.ca/site/projects/ astronomy_files/parallax.swf Stars perpendicular to Earth-Sun plane http://www.ifa.hawaii.edu/ ~barnes/ast110_10/stars/ parallax_of_nearby_star.swf The Greeks knew that the lack of observable parallax could mean one of two things: 1. Stars are so far away that stellar parallax is too small to notice with the naked eye. 2. Earth does not orbit the Sun; it is the center of the universe. With rare exceptions such as Aristarchus, the Greeks rejected the correct explanation (1) because they did not think the stars could be that far away. Thus, the stage was set for the long, historical showdown between Earth-centered and Sun- centered systems. © 2014 Pearson Education, Inc.  What have we learned? What was so mysterious about planetary motion in our sky? – Like the Sun and Moon, planets usually drift eastward relative to the stars from night to night, but sometimes, for a few weeks or few months, a planet turns westward in its apparent retrograde motion. Why did the ancient Greeks reject the real explanation for planetary motion? – Most Greeks concluded that Earth must be stationary, because they thought the stars could not be so far away as to make parallax undetectable. © 2014 Pearson Education, Inc.