* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Document
Astronomical clock wikipedia , lookup
History of astronomy wikipedia , lookup
Antikythera mechanism wikipedia , lookup
Chinese astronomy wikipedia , lookup
Aquarius (constellation) wikipedia , lookup
Rare Earth hypothesis wikipedia , lookup
Late Heavy Bombardment wikipedia , lookup
Corvus (constellation) wikipedia , lookup
Astronomy on Mars wikipedia , lookup
Extraterrestrial life wikipedia , lookup
History of Solar System formation and evolution hypotheses wikipedia , lookup
Formation and evolution of the Solar System wikipedia , lookup
Lunar effect wikipedia , lookup
Geocentric model wikipedia , lookup
Satellite system (astronomy) wikipedia , lookup
Tropical year wikipedia , lookup
Comparative planetary science wikipedia , lookup
Lunar theory wikipedia , lookup
Astronomical unit wikipedia , lookup
Dialogue Concerning the Two Chief World Systems wikipedia , lookup
Lecture 3 ASTR 111 – Section 002 Terms • • • • • • • • • • • Apogee/Perigee Subtend Parsec, light-year, AU Parallax Solar and Sidereal time Small angle formula Ecliptic Zenith Tropic of Cancer, Capricorn, Artic and Antarctic Circle Equinox, Solstice Zodiac Notes on Lecture Notes • Sent out Tuesday afternoon/evening • I suggest that you print them out and bring them to class • I will also post PowerPoints • If you have problems with the file, email me! Outline 1. 2. 3. 4. 5. Quiz Discussion Rotation – review generally The Seasons – finish lecture tutorial The Moon in its orbit Math Review – converting units and scientific notation #3 • In class, we estimated the angular separation of two points on the screen that were separated by 10 feet. Suppose that these two points were separated by 1 AU. How far away from the screen would you need to walk so that the dots appeared to subtend 1 arc-second? A B Gods-eye view Observer’s view “ #4 • How many light-years are in 10 parsecs? 10 parsec 3.26 light - year x 32.6 light - years 1 1parsec • How many parsecs are in 5 light-years? 5 light - year 1 parsec x 1.3 parsec 1 3.26 light - year Units conversion • Start with a relationship like – 1 degree = 60 arcminutes – To convert from degrees to arcminutes, set up a ratio so the unit you want to get rid of cancels – Example: how many arcminutes is 0.5 degrees? 0.5 degree 60 arcminutes 30 arcminutes 1 1 degree Units conversion • Start with a relationship like – 1 parsec = 3.26 light-years – To convert from parsec to light years, set up a ratio so the unit you want to get rid of cancels – Example: How many light-years are in 5 parsecs? #6 • In the image, suppose that a star in the constellation Cygnus appears exactly at an observer's zenith (the dotted line) at 8 pm local time. After 24 solar hours have passed, where would the constellation appear to be? Outline 1. 2. 3. 4. 5. Quiz Discussion Rotation – review generally The Seasons – finish lecture tutorial The Moon in its orbit Math Review – converting units and scientific notation Thinking about rotation With parallax, we learned that the position of a near object relative to a distant object can change if the observer moves. With rotation, the time it takes for the position of a near object to change relative to a distant object can be different if the observer moves. Thinking about rotation In the last lecture I had you do an experiment with a quarter to illustrate this point: When one object “B” rotates about another object, the number of times it rotates with respect to something in the distance depends on if “B” is rotating on its axis. Slippage Meaning • When you skid a tire, there is slippage – same part of tire always touches ground • When you roll a tire, there is no slippage – different parts of tire touch ground George B looking straight to the left (at a distant object) B Table I can get him across the table by “skidding” or “slipping” – the 9 always touches the table. In this case he always is looking to the left at the distant object. B Table Instead of “skidding” or “slipping”, he can “roll”. On a flat table, he will look at same place in distance after 1 revolution – or after he has “rolled” the distance of his circumference Table B Group Question • Rotate B around A with slippage. How many times does George B look straight to the left? – • With slippage, the 9 on the top quarter always touches the bottom quarter Rotate B around A without slippage (like a gear). How many times does George B look straight to the left? – Without slippage, first the 9 in the 1993 on the top quarter touches the bottom quarter, then 1 then the “In God We Trust”. B A (A is glued to the table) Group Question • Rotate B around A with slippage. How many times does George B look straight to the left? – • With slippage, the 9 on the top quarter always touches the bottom quarter One time Rotate B around A without slippage (like a gear). How many times does George B look straight to the left? – Without slippage, first the 9 in the 1993 on the top quarter touches the bottom quarter, then 1 then the “In God We Trust”. Two times B A (A is glued to the table) With slippage A B B B B The nine on B always touches A Without slippage B George B is looking to the left again here! B A B B “rolls” on A, in the same way a tire rolls on the ground. B Note: George B only looks directly at George A’s center one time right about here Summary • When the coin slipped across the table, it did not rotate at all. When a coin slipped around another coin, it rotated once with respect to the “distance”. • When a coin rolled across a table the distance of its circumference, it rotated once. When it rolled the same distance, but around another coin, it rotated twice with respect to the “distance”. What to know • When thinking about rotation, you need to account for rotation about its own axis and rotation about another object. • The number of times you see something in the distance will be different than the number of times you look at the object that you are rotating around. Top view of classroom Someone in back of room (distant object) Stage Student Instructor Or Sidereal Time = star time Sidereal Day = the length of time it takes for a star to repeat its position in the sky. Solar Time = sun time Solar Day = the length of time it takes the sun to repeat its position in the sky. Sidereal Time = star time Solar Time = sun time At 1, line points atLine sun1 goes and through distant sun and star distant star • Sidereal Time = star time • Solar Time = sun time Line At 1,1 goes line through points sun and1 atLine sun distant goes and star through distant sun and star distant star At 2, 24 sidereal hours since 1, line is now pointing at distant star only • Sidereal Time = star time • Solar Time = sun time • Which is longer? 1. Sidereal day 2. Solar day At 1, line points at sun and distant star At 2, 24 sidereal hours since 1, line is now pointing at distant star only • Sidereal Time = star time • Solar Time = sun time • Which is longer? 1. Sidereal day 2. Solar day by ~ 4 min. At 1, line points at sun and distant star At 2, 24 sidereal hours since 1, line is now pointing at distant star only Key • A solar day is longer than a sidereal day • This means it takes longer for the sun to repeat its position in the sky than a distant star Which way is Andromeda at 8:00 pm local time for the person in California? 1. West 2. East 3. Vertical Where is Cygnus 24 sidereal hours later? 1. West 2. East 3. Vertical Where is Cygnus 24 solar hours later? 1. West 2. East 3. Vertical Outline 1. 2. 3. 4. 5. Quiz Discussion Rotation – review generally The Seasons – finish lecture tutorial The Moon in its orbit Math Review – converting units and scientific notation What causes the seasons? 1. Distance of the sun from earth 2. Tilt of Earth with respect to the ecliptic 3. Both 4. None of the above 5. Primarily 2., but with a small contribution from 1. What causes the seasons? 1. Distance of the sun from earth 2. Tilt of Earth with respect to the ecliptic which causes • • Change in length of time sun is visible Change in height of sun in sky 3. Both 4. None of the above 5. Primarily 2., but with a small contribution from 1. The ecliptic is the imaginary plane that the Earth moves on as it rotates around the sun The Celestial Sphere • Sometimes it is useful to think of the stars and planets as moving along a sphere centered on Earth Important! The angle of the light to the ground. The two circled yellow arrows point to the same line of latitude. The right arrow is perpendicular to surface. The left arrow is less than perpendicular to surface. Thinking about light • It is often useful to think of photons as very small particles. • When I point a flashlight at you, you are getting hit with a bunch of little pellets. • Suppose you were hit by 10 pellets in an area the size of a quarter. • How does this compare with getting hit with 10 pellets over an area the size of a book? • See Seasons Lecture Tutorial at end A D F Outline 1. 2. 3. 4. 5. Quiz Discussion Rotation – review generally The Seasons – finish lecture tutorial The Moon in its orbit Math Review – converting units and scientific notation Eventually we want to be able to explain … A simple model • Moon executes circular orbit • Moon orbit is in Earth’s ecliptic plane What is wrong with this picture? B Earth C View of Moon from Earth at one of the positions (A-E) above. Sun’s rays A 1. Fill in the dark and light parts of the Moon for A-D (from this perspective) 2. From the perspective of someone on Earth what position of A-E best fits the Moon view in the E lower-left-hand corner? 3. In the blank boxes below, sketch how the Moon would appear from Earth from the four Moon D positions that you did not choose for Question 2. Label each box with a letter. F H Earth I View of Moon from Earth from one of the positions (F-I) above. Sun’s rays G 4. Shade in the part of the Moon that is not illuminated by the sun when it is at positions F-I. 5. Which Moon position (FI) best corresponds with the Moon phase shown in the lower-left corner? 6. How much of the Moon’s surface is illuminated by the sun during this phase? 7. How much of the Moon’s illuminated surface is visible from Earth for this phase of the Moon? Model can explain the phases of the Moon • The phases of the Moon occur because light from the Moon is actually reflected sunlight • As the relative positions of the Earth, the Moon, and the Sun change, we see more or less of the illuminated half of the Moon. What does the Earth look like from the Moon at • • • • Full Moon New Moon First Quarter Third Quarter What are 2 observations simple model does not predict? 1. 2. What are 2 observations simple model does not predict? 1. Why there are not eclipses every month 2. Why there are “annular” and “total” eclipses Eclipses occur only when the Sun and Moon are both on the line of nodes What are 2 observations simple model does not predict? 1. Why there are not eclipses every month 2. Why there are “annular” and “total” eclipses of the sun Solar eclipses can be either total, partial, or annular, depending on the alignment of the Sun, Earth, and Moon Lunar eclipses can be either total, partial, or penumbral, depending on the alignment of the Sun, Earth, and Moon Question • If you were looking at Earth from the side of the Moon that faces Earth, what would you see during – A total lunar eclipse? – A total solar eclipse? The Moon’s rotation always keeps the same face toward the Earth due to synchronous rotation Time and the Moon • Two types of months are used in describing the motion of the Moon. • With respect to the stars, the Moon completes one orbit around the Earth in a sidereal month, averaging 27.32 days. • The Moon completes one cycle of phases (one orbit around the Earth with respect to the Sun) in a synodic month, averaging 29.53 days. • • • • sidereal month, averaging 27.32 days. sidereal day – 23 hr 56 min synodic (lunar) month, averaging 29.53 days. solar day – 24 hr Question • On a certain date the Moon is in the direction of the constellation Gemini as seen from Earth. When will the Moon next be in the direction of Gemini? 1. One year later? 2. 366.2425 days later? 3. One sidereal month later? 4. One synodic month later?