2Earth rotates on its axis and simultaneously revolves or orbits around the Sun. Which of these two motions is responsible for each of the following:SunEarthEarth
3The sun rises in the east and sets in the west Is this because the Earth rotates on its axis, or because the earth orbits the sun?
4The sun rises in the east and sets in the west Is this because the Earth rotates on its axis, or because the earth orbits the sun?The earth rotates on its axis from east to west.
5Different constellations appear in the summer than in the winter Is this because the Earth rotates on its axis, or because the earth orbits the sun?
6Different constellations appear in the summer than in the winter because of the Earth’s orbit around the sun.+10+10SunEarthEarth−10−10OphiuchusOrionFIGURE The night sky changes with the seasons because Earth is continuously changing positions as it orbits the Sun.Observed region of night sky during one seasonObserved region of night sky six months later
7Orion’s BeltThe ancient Greeks saw this…….and imagined this!
8At night, stars in the Northern Hemisphere appear to revolve around the North Star Is this because the Earth rotates on its axis, or because the earth orbits the sun?
9At night, stars in the Northern Hemisphere appear to revolve around the North Star Is this because the Earth rotates on its axis, or because the earth orbits the sun?The stars seem to rotate because the Earth rotates on its axis.
10Moon revolves around Earth while Earth rotates on its axis Which of these two motions is responsible for the following?
11The moon rises in the east and sets in the west, just like the sun. Is this because the earth rotates on its axis or because the moon orbits around the earth?
12The moon rises in the east and sets in the west, just like the sun And like the sun, it is because the earth rotates on its axis.
13The moon rises approximately 53 minutes later each day. Is this because the earth rotates on its axis or because the moon orbits around the earth?
14The moon rises approximately 53 minutes later each day. The moon rises once a day because the earth rotates on its axis.Its 53 minutes later each day, because the moon orbits the earth and therefore moved “forward” by a small amount.
15Why the moon rises later each night Full moon rises at about sunset.In 24 hours, the earth makes a complete rotation, but the moon has move ahead on its orbit, so the earth must rotate “a bit extra” for the moon to rise above the horizon. This extra bit is about 53 minutes.
16The moon passes through monthly phases The moon passes through monthly phases. Is this because the earth rotates on its axis or because the moon orbits the earth?
17The moon passes through monthly phases. The moon passes through monthly phases. Is this because the earth rotates on its axis or because the moon orbits the earth?The phase of the moon depends where it is in its orbit around the earth.
18Why are there phases of the moon? The moon only reflects light from the Sun.When the moon is at point E (farthest from sun), entire lit face can be seen.At point A, only dark side points towards Earth.B-D, F-H, occur in between full moon and new moon.
19Planets Move independently of stars. Sometimes appear to move “backwards” relative to other heavenly bodies (“retrograde motion”).Larger and brighter than most stars.Don’t twinkle because they are much closer than stars.
20Aristotle and the Geocentric (Earth-centered) Universe All heavenly bodies orbited the Earth, including the Sun:People have no sensation of motion so it must be the sky that movedPeople do not fall off the Earth, so it must not be moving (at least not suddenly)Stars position relative to each other never changesModified by Ptolemy to explain retrograde motion of planets.
22The Renaissance and the Heliocentric Solar System
23The Beginning: Copernicus (1473-1543) Polish astronomer found Ptolemaic system too complicatedProposed a heliocentric (sun-centered) model that was more simple than Ptolemy’s adaptation of Aristotles’s modelNot censored by the Church at the time, but also not widely circulated.
24Brahe & KeplerBrahe ( ) mapped all known objects in the sky, but did not explain their motions.Kepler ( ) Brahe’s assistant, who believed in the heliocentric theory, proposed the idea of elliptical orbits for planets.
25Galileo (1564-1642) – the Father of Modern Science the Scientific Method: the laws of nature must be understood by observation, experimentation, and analysis.Developed a telescope far better than those of previous astronomersUsed his observations of heavenly motions and analysis of earthly motion to question the geocentric model
26Galileo – Study of Physics Law of Inertia – the tendency for an object to resist a change in motion. People living on a planet moving at a constant speed would realize no motion, unless it were suddenly accelerated.
27Galileo – Study of Milky Way and Moon with telescope contradicts Aristotle’s Ideas Saw Milky Way was a collection of individual stars, not a cloud of light.Realized the Moon was not an unblemished body.
28Therefore it would always appear as a crescent. FIGURE (A) In Ptolemy’s theory,Venus could never move farther from the Sun than is shown by the dotted lines.Therefore it would always appear as a crescent.Fig a, p.567
29Final Proof for Galileo of the Heliotropic Solar System Moons of Jupiter orbited Jupiter, not the Sun.Phases of Venus not possible for in a geocentric configuration.
30Galileo was persecuted by the Roman Catholic Church for his beliefs
31Isaac Newton ( )Why do planets orbit around the Sun, instead of flying off into space?Newton's work combined the contributions of Copernicus, Kepler, Galileo, and others to answer this question by explaining the unversal laws of gravity and motion
3222.4 The motions of the Earth and the Moon By 1700, the heliocentric system was well establishedrotation – the Sun and planets spin on their axesRevolution – the Earth traveling around the sun in its orbitPrecession – the wobble of Earth’s axis
33Figure The night sky changes with the seasons because the Earth is continuously changing positions it orbits the Sun.Fig , p.535
34Figure The Earth’s axis wobbles or precesses like a top, completing one precession cycle every26,000 years.Fig , p.536
35The Moon Revolves around Earth in 29.5 days Rotates on its axis in 29.5 daysNew moon – when the moon is darkCrescent moon – four days laterGibbous moon – bright moon 10 days afterFull moon – days after the new moonWaning moon – as it shrinks toward the next new moon
36Orbital plane of earth and moon The Moon’s plane of orbit is tilted 5.2o relative to that of the EarthThus the Earth’s shadow misses the full moon.The new moon’s shadow usually misses the Earth.
37Eclipses of the Sun and Moon If the Moon passes through the Earth–Sun plane when the three bodies are aligned properly, then an eclipse will occur
38Eclipses of the Sun and Moon Solar eclipse – when the Moon passes directly between Sun and EarthUmbra – the region of shadow exhibiting total eclipsePenumbra – the edge of shadow showing partial eclipseLunar eclipse – When the Earth lies in line between the Moon and the Sun.Last longer and more common as Earth has a bigger shadow
39Figure A total solar eclipse is viewed in the narrow band, called the umbra, formed by the projection of the Moon’s shadow on the Earth. The penumbra is the wider band where a partial eclipse is visible. (Drawing is not to scale.)Fig , p.540