Download Why We Have Seasons

Why We Have Seasons? * tilt of the earth’s rotation axis with respect to the ecliptic
(combined with Earth’s revolution around the Sun)
* ARNT caused by the changing distance from the Earth to the Sun that results from the
shape of Earth’s orbit.
– axis is tilted –revolve around the sun
The Ecliptic
- Straight path on the celestial sphere the sun traces
- A plane (described by earths path around the sun)creates 2(plane rep. earths orbit)
Kepler (Johannes) – favored the Copernican Model
- used Tycho’s data for the motion of mars to figure out the nature of planetary
orbits
- model was precice and did not require use of epicycles (<- no such thing as)
- laws describe orbital shapes, changing speeds and the lengths of planetary years
- Law #1~ orbits of planets are ellipses with sun at 2 of the focal points
o Explains perihelion and aphelion
- Law #2~ (line joining the) Planets sweep out equal areas in equal amounts of time
o Explains apparent variable motion of the sun
- Law #3 ~ square of a planet’s sidereal period around the sun is directly proptional
to the cube of the length of its orbits semi major axis
o Explains higher orbital velocities of inner planets
Newton
- showed Keplers laws can be derived from his 3
- found the formula to express the force of gravity
- able to mathematically to describe the orbits of the planets and their satellites, the
moon, comets, asteroids
- laws were used by friend, Edmond Halley to predict the reappear of a comet
- also used by Adams and Leverrier to find a planet beyond the orbit of Uranus,
based on slight irregularities in that planets orbital motion: Neptune
- Law #1- a body remains at rest or moves in a straight line at a constant speed
unless acted upon by a net outside source (the law of inertia)
o Planets would leave their orbits if no forced acted on them
- Law #2- acceleration of an object is proportional to the force action up it
o Force equals mass times acceleration
- Law #3- whenever one body exerts a force on the 2nd body the 2nd exerts on equal
and opposite force on the 1st
o The law of “action and reaction”
Retrograde motion – Planets seem to have stop and then back up for the reverse
movement to the west relative to the background stars
Tycho Brahe ~most accurate observational astronomer (pre-telescope)
- observed a new star in Cassiobeia and comets with no parallax
- believed the sun revolved around the earth
- kept accurate records of the planetary obsercations over a period of about 20 years
-
hired Kepler as his assistant
died because he drank to much and couldn’t go to the bathroom (socially wrong)
Copernicus- model is complex and required the use of epicycles
- planets closer to the sun move faster
- worked out a relative seate(?) for the solar system
- earth to the sun distance is one AU (astronomic units)
Renaissance Astronomy – Copernicus, Tycho Brahe, Kepler, Galileo, Newton
Aristotle – he observed earth centered shadow on the moon during a lunar eclipse
- knew that ones view of the sky changed with travel north or south
- concluded that earth was a sphere
- understood the cause of lunar phases
Aristarchus (heliocentric model)
- measured the relative distances to the moon and sun
- realized that the sun was much larger than the earth
- put earth in orbit around the sun even though he had no proof (parallax)
Eratosthenes- measured the earth’s circumference
- At Alexandria measured the points by using the sun (7 degrees(
Hipparchus
- Made accurate observations/produced a catalog of 850 plus stars
- Revived a magnitude scale to compare star brightnesses
- Detected slight change in the norm celesnalpede
- Determined the length of the year to within 6 minutes
- Recognized the sun’s annual apparent motion was irregular; the sun appeared to
move faster new the winter solstice and slower at summer solstice
- Explained how planets could move from direct retrograde motion and still orbit
earth
Ptolemy
- earth centered cosmology which remained in favor into the 1400’s
- complied the almagest, a collection of material from earlier astronomers
- explained retrograde with epicycles and circular planetary orbits
- produced one of the earliest accurate maps of the Mediterranean region
- though the earth’s circumference was only 19.000 miles
Scientific notation- “powers of ten”(much larger or smaller then one)