Astronomy

1
Astronomy

• Celestial Observations

2
The Celestial Sphere

• All celestial objects, (sun, stars, moon,
  planets), from Earth appear to be on the surface
  of an imaginary sphere surrounding Earth.
• This imaginary sphere is called the Celestial
  Sphere.

3
(No Transcript)
4
Celestial Observation Terms

• Horizon where celestial sphere meets Earth.
• Zenith point on celestial sphere directly above
  observers position.
• Altitude objects distance, in degrees, above
  horizon.
• Azimuth objects distance, in degrees, measured
  clockwise from due north position (due north is
  00 azimuth).

5
(No Transcript)
6
Star Paths

• All celestial objects appear to move from east to
  west across the sky in an arc. Why?
• Circumpolar stars move in counterclockwise
  circles between the northern horizon and Polaris
  and never set.

7
Rotation

• The apparent daily motion of celestial objects is
  due to Earths rotation.
• Rotation is the turning of an object on its axis.
• Celestial objects are not actually moving from
  east to west across the sky, rather the earth is
  rotating under them.

8
(No Transcript)
9
Rotations
10
Revolution

• Revolution is the movement of one celestial
  object around another.
• The path along which an object travels during a
  revolution is called an orbit.

11
Earths Revolution
12
Orbits
13
What are Constellations?

• Constellations are stars that appear to be
  grouped in patterns that form the outlines of
  things (people, animals, objects).
• The night sky is divided into 88 constellations.
• Circumpolar constellations are those
  constellations that are always visible as they
  never set below the horizon.

14
(No Transcript)
15
(No Transcript)
16
Star Shifts

• Constellations shift, rise and set, (similar to
  the rise and set of the Sun) during a night due
  to the rotation of the Earth.
• Constellations in the sky slowly change from one
  night to the next as a result of the revolution
  of Earth around the sun.
• Constellations rise approximately 4 minutes later
  each night.

17
(No Transcript)
18
Planetary Motions

• On a daily basis planets and stars appear to move
  from east to west.
• Over long periods of time the planets appear to
  move eastward relative to the stars behind them.

19
Celestial Models

• Geocentric Theory this theory, put forward by
  the ancient Egyptian astronomer Ptolemy, states
  that the Earth is the center of the universe.

• Heliocentric Theory this theory, put forward by
  the Polish scientist Copernicus, states that the
  Sun is the center of the universe.

20
Ptolemy and Geocentric Theory
21
(No Transcript)
22
Copernicus and Heliocentric Theory
23
Orbital Forces

• Johann Kepler developed the Laws of Planetary
  Motion which states that planets orbit in
  ellipses.
• Unlike a circle the center of an ellipse consists
  of two fixed points called foci.
• Keplers First Law
• The orbits of the planets around the Sun are
  ellipses, with the Sun at one of the foci.

24
Keplers Laws

• Keplers second law states that
• An imaginary line joining a planet to the Sun
  will sweep over equal areas in equal periods of
  time.
• Perihelion when the planet is closest to the
  Sun (moving the fastest).
• Aphelion when the planet is farthest from the
  Sun (moving the slowest).

25
Evidence of Earths Rotation

• Foucault Pendulum the greater the latitude the
  greater the hourly change in direction.
• Coriolis Effect is the tendency of matter moving
  across the Earths surface to be deflected from a
  straight-line path.
• Other evidence includes the day night cycle, star
  paths and satellite photos.

26
Apparent Motions of the Sun

• Due to the rotation of the Earth, the Sun appears
  to move in an arc across the sky from east to
  west.
• The tilt of the Earths axis, 23.50, causes the
  location of the direct rays of the Sun to change
  in a cyclic pattern.

27
Change of Seasons

• Three factors cause the seasonal changes
• Earths revolution around the sun
• Tilt of the Earths axis
• Parallelism of the axis

28
Time and Earth Motions

• Sidereal day is the time period for Earth to make
  one complete rotation on its axis (23 hrs, 56
  min, 4 sec.).
• Apparent solar day is about 4 min longer (based
  on solar noon to solar noon) to account for the
  additional rotation needed as a result of Earths
  revolution around the sun.
• Since our orbital speed varies, therefore the
  apparent solar day varies, the mean solar day (24
  hrs) is used for daily timekeeping.

29
Moon Motions

• Moon orbits earth once every 27 1/3 days.
• The barycenter is the gravitational center the
  Earth and Moon revolve around (1700km beneath
  surface of Earth).
• Sidereal month (27 1/3 days) is time for the Moon
  to revolve around the Earth.
• Synodic month (29 ½ days) is the time for the
  Moon to complete a cycle of phases.

30
Phases of the Moon

• The illuminated portion of the moon that faces
  Earth varies in a cyclic pattern called phases.
• New moon when the entire illuminated portion is
  facing away from Earth.
• Waxing period when right hand portion seems to
  grow more lighted.
• Full moon when the entire illuminated portion
  is facing toward Earth.
• Waning period when the left hand portion
  shrinks in illumination.

31
(No Transcript)
32
(No Transcript)
33
(No Transcript)
34
Eclipses

• Solar eclipse occurs when the Moon passes between
  the Earth and the Sun.
• Umbra is the part of the Moons shadow in total
  darkness
• Penumbra is the part of the Moons shadow in
  partial darkness.
• Annular eclipse occurs when the Moon is at apogee
  and the outer edge of the Sun is visible.
• Lunar eclipse occurs when the moon passes through
  the Earths shadow.

35
Solar and Lunar Eclipse
36
(No Transcript)
37
(No Transcript)
38
(No Transcript)