Transcript Astronomy

Astronomy
Study of the moon, stars, planets and
other objects in space
Vocabulary
•
•
•
•
•
•
•
•
Geocentrism
Heliocentrism
Inertia
Gravity
Ellipse
Rotation
Revolution
Axis
• Solstice
• Equinox
“The Earth is Flat”
• Early Europeans
believed that the earth
was flat-if one sailed
far enough, they would
fall off the edge of the
earth
• Exploration by
Columbus disproved
the myth as did
calculations by early
scientists
A Brief History
• Ancient Greeks -observed the sky and the
constellations
• Named the planets “wandering stars”
because they seemed to move into different
positions in the sky
• Believed that earth is surrounded by rotating
dome called the celestial sphere
• Believed the earth was the center of the
universe-geocentricism
A Brief History, cont.
• Copernicus-had the idea that the sun
was the center of the universe-
heliocentricism
• The earth and the other planets
revolved around the sun
• Galileo-first scientist to view space
through a telescope-found further
evidence to support the heliocentric
model of the universe
Planetary Orbits
• Tycho Brahe-made observations about
the positions of the planets
• Johannes Kepler-figured out that the
orbits of planets around the sun are not
circular, but ellipses
• Ellipse-an elongated circle or oval shape
Inertia and Gravity
• Issac Newton-discovered that the forces
of inertia and gravity keep the planets
in their positions in space
• Inertia-a moving object will stay in
motion; a stationary object will remain
in place
• Gravity-attractive force between two
objects-force depends on the mass and
the distance between them
Gravity
• Everything on earth is affected by
gravity
• The earth has gravity due to its mass
• Earth’s gravity pulls everything on earth
towards its center
• Every living thing also has gravity
because every living thing has mass-so
they are pressing up and away from the
earth
Gravity, cont.
• Gravity holds all the planets in orbit
around the sun
• Planets, sun, moons all have mass and
gravity
• Without gravity, the planets would
move through space through their
inertia
Earth’s Rotation
• Axis-imaginary line that passes
through the earth at the North
and South Pole
• Rotation-earth’s spin on its axis
causes day and night
• Earth rotates counter-clockwise
so the sun appears to move
from east to west
• Rotation of the earth on its
axis takes approximately 24
hours or 1 day
Earth’s Revolution
• Revolution-movement of
one object around another
object
• Orbit-the path an object
travels in its revolution
• Earth’s orbit is not a circle,
but more oval shaped
• The earth takes about one
year to travel around the
sun
Leap Year
• Earth’s orbit around the sun takes 365¼
days
• Our calendar year is based on 365
days/year
• To take into account the ¼ fraction of a
day, one day is added to the month of
February every four years-called Leap Year
• Leap Year is 366 days long
Seasons
• Sun’s rays hit the earth more directly at
the equator and are more spread out
near the poles
• Earth’s Tilt-the earth is not straight up
and down, but is tilted 23.5°
• The earth has seasons because it is
tilted on its axis
Seasons, cont.
• Earth is tilted toward the sun for part of the year
and away from the sun for the other part
• Hemisphere tilted toward the sun-Summer
• Hemisphere tilted away from the sun-Winter
• Neither hemisphere tilted toward or away from
the sun-Spring and Fall
• Distance from the sun has nothing to do with the
seasons-when the earth is at its greatest distance
from the sun it is summer in the Northern
Hemisphere
Sun’s angle at different times of
the year
Solstice and Equinox
• Both occur twice a year
• Summer Solstice (June 21) and Winter
Solstice (December 21)
Shortest
and Longest daylight hours of the year
• Autumnal (Fall) Equinox (September 23)
and Vernal (Spring) Equinox (March 21)
Light and dark hours are equal