The Origin of Modern Astronomy Nicolai Copernicus (1473-1543)
Goals for Today Complete our study of the Moon: lunar phases, the Sun-Earth-Moon geometry, and the eclipses Tides and their origin Earth's place in the cosmos; a little bit of history
Assigned Reading Unit 10: Geometry of Sun, Earth, and Moon Unit 19: Tides Units 11 and 12: Understanding the Motions of Planets, and the Birth of Modern Astronomy
Announcements Homework # 1 starts today; it is due on Thursday, Sept 29th Astronomy Helpdesk is now available: Mondays through Thursdays, 7-9 pm, in Hasbrouck 110
Lunar Phases
Survey Question A third quarter moon is rising. What time is it? 1) sunset 2) sunrise 3) midnight 4) noon
Survey Question A third quarter moon is rising. What time is it? 1) sunset 2) sunrise 3) midnight 4) noon
Earth Rising on the Moon Apollo 11
Survey Question In this picture of the Earth rising, what is the predominant direction of the sun in relation to the observer? 1) above the observer 2) below the observer 3) behind the observer 4) behind the Earth
Survey Question In this picture of the Earth rising, what is the predominant direction of the sun in relation to the observer? 1) above the observer 2) below the observer 3) behind the observer 4) behind the Earth
Solar Eclipses
The Sun is physically 400 times larger than the Moon.! Why can it be obscured by the Moon?!
Angle diameter (in radians) = diameter/distance Full circle = 2! (in radians)=360 degrees=360 o 1 o =60 arminutes = 60 1 = 60 arcseconds = 60 The Sun is 400 times further away than the Moon
Angular Size Some Examples:! Horizon to zenith (point overhead)!! 90 o! Your fist at arm's length!!!! 10 o! Sun or Moon seen from Earth!!0.5 o = 30'! Smallest detail visible to naked eye! 1' = 60''!! Smallest detail visible by a single telescope from!earth's surface:!1''!! Angular size of Pluto: 0.15!! Betelgeuse (largest star) seen from Earth 0.004''!!
Geometry of Moon and Sun Both the Moon and the Sun have angular diameter of about 0.5 degree, the exact value at a given time depending on the exact distance. Therefore, we can periodically have solar eclipses
!! Geometry of Solar Eclipses
Looking Back on an Eclipsed Earth; 1999 August 11! Credit: Mir Space Station Crew!
Annular Eclipse October 3, 2005
Total and Annular Eclipse
It takes about an hour for the moon to cover the sun. Why? The moon moves at an angular speed of! 360 deg/(28x24 hr) = 0.5 deg/hr.!! The angular size of the moon is about 0.5 deg.!!
How come there isn't an eclipse every full moon and new moon? The main reason is that the moon s orbit is tilted from the earth s orbit.!! However, twice a year the nodes of the moon s orbit will align with the Earth-Sun direction, and total eclipses will be possible.!! A total eclipse from a given point on the surface of the Earth is not a common occurrence. For example, next solar eclipse in the USA will occur on 21 August 2017; the following one will be on 8 April 2024.!
Survey Question The phase of the moon at a solar eclipse is? a) new b) 1 st quarter c) full d) it depends on the year
Survey Question The phase of the moon at a solar eclipse is? a) new b) 1 st quarter c) full d) it depends on the year
Lunar Eclipse (the Moon in the Earth s Shadow)!!
Effects of Moon on Earth: Tides To sun
Spring Tides Occur at every new and full moon
Neap tides! Occur at every first- and third-quarter moon
Friction drags the tidal bulges eastward out of the direct earth-moon line Earth's rotation slows down by 0.0023 s/100 years.! Only 900 million years ago, Earth' day was 18 hrs long.! The moon's orbit is growing larger by about 4 cm/yr.!
We see only one side of the moon, because the tidal friction has slowed the rotation of the moon so that its rotation and revolution are synchronized
And Now, Onto the Discussion of the Birth of Modern Astronomy!
Archeoastronomy There is evidence that Human kind has paid very closed attention to the sky, its motions and periodicity. Archeoastronomy is a blend of superstition, astrology, religion, but also common sense Greeks were the first to try to understand (logically) the universe. Pythagoras: universe ruled by geometrical, mathematical relationship --- This notions still fundamental today All ingredients there for the methods of modern science: have a theory and test it against reality the theory may or may not survive Ultimately, Greek science still a blend of scientific method and philosophical believes. True scientific method had to wait for Galileo
Not to scale
Aristotle Universe: Three Basic Assumptions The Earth was at the center of the Universe. The only motion in the heavens was uniform circular motion The heavens were more perfect than the Earth, and objects in the heavens were eternal.
"Common Sense" If the Earth actually spun on an axis, why didn't objects fly off the spinning Earth? If the Earth was revolving around the sun, why didn't it leave behind the birds flying in the air? If the Earth were actually on an orbit around the sun, why wasn't a parallax effect observed?
Two problems for the Geocentric model: (1) Change of brightness (2) Retrograde Motion Ptolemy Solution: add a special fix: epicycle (circle on circle) Brightness changes because of distance change
Ptolemic Model
The Copernican Revolution: The Heliocentric System Nicolai Copernicus (1473-1543). "The Sun, not the Earth, was the center of the Solar System. "The Earth is just another planet (the third outward from the Sun), and the Moon is in orbit around the Earth, not the Sun. "The stars are distant objects that do not revolve around the Sun.
Retrograde Motion and Varying Brightness of the Planets " The planets in such a system naturally vary in brightness because they are not always the same distance from the Earth. " The retrograde motion could be explained in terms of geometry and a faster motion for planets with smaller orbits.
Galileo Galilei Galileo discovered that:! our Moon has craters (is a `mound of rocks );! Jupiter has it's own moons;! the Sun has spots;! Venus has phases like our Moon; The `heavens are imperfect! (1564-1642), Italian These discoveries confirmed the Copernican hypothesis that the Earth was just another planet.
Imperfect and Changing Universe Sun had dark patches on Sun. The motion of such sunspots indicated that the Sun was rotating on an axis. Jupiter had 4 moons; thus planets could have moons circling it that would not be left behind as the planet moved around its orbit The Moon was not smooth, but was covered by mountains and craters.
The Phases of Venus Venus goes through a complete set of phases, just like the Moon. This was the first empirical evidence that allowed a definitive test of the geocentric and heliocentric models.
The introduction of the `scientific method (formulate an hypothesis, test the hypothesis against reality, verify or discard the hypothesis if data do not confirm it) marks the birth of Modern Science, and Astronomy