Transcript Earth`s Motions

Movement
Rotation and Revolution
• Rotation- earth
spins on its axis
– Creates day and
night (24 hours)
– Tidal bulge
• Revolution- earth
orbits around sun
– Creates year
(365.25 days)
Doppler Effect
• the apparent change in wavelength of light
that occurs when the object is moving
toward or away from the Earth.
• Using the spectroscope, astronomers can
determine whether a particular object is
moving toward Earth or away from Earth
Ex) Ambulance Siren:
Approach observer: High pitch ;
Move away from observer: low pitch
BLUE SHIFT
RED SHIFT
Object approaching
earth
Object moving away
from earth
Light waves are
compressed (pushed
together)
Light waves are
expanded
Wavelengths appear
shorter (blue end of
spectrum)
Wavelengths appear
longer (red end of
spectrum)
Larger Doppler shifts indicate higher
speeds and smaller Doppler shifts indicate
slower speeds.
Larger Doppler shifts indicated higher speeds
and smaller Doppler shifts indicate slower
speeds.
B
R
B
R
What Shift is Shown?
What Shift is Shown?
Remember, the greater the amount of shift,
the faster the star is moving!
Helium
Helium slightly red shifted. Moving away.
Helium more red shifted. Moving away even faster!
ELEMENTAL SPECTRA PRACTICE
Big Bang
• A theory that explains the origin of the
universe
• Began as a singularity that started to
expand and continues to expand today
• Evidence
– Red shifts of galaxies
– Cosmic Background Radiation (CBR)
• Is there an end to the Big Bang?
– Big Crunch
– Ever-expanding universe
Hubble’s Law
• States that galaxies are moving away from
each other at a speed proportional to their
distance from each other
– The farther away, the faster they move
• each raisin will see all other raisins moving
away from it as the loaf expands
Earth’s Orbit and Seasons
Precession
• gradual shift in the orientation of Earth's axis of rotation
• Cause: the gravitational forces of the Sun and the Moon,
and to a lesser extent other bodies
– is similar to the precession of a spinning top
• Effects:
– the positions of the south and north celestial poles
appear to move in circles against the space-fixed
backdrop of stars
– the position of the Earth in its orbit around the Sun at
the solstices, equinoxes, or other time defined relative
to the seasons, slowly changes
http://earthobservatory.nasa.gov/Features/Milankovitch/Images/milankovitch_precess_high.mov
Precession
Nutation
• is a rocking, swaying, or nodding motion in the
axis of rotation of a largely axially symmetric
object
• happens because of tidal forces that cause the
precession of the equinoxes to vary over time so
that the speed of precession is not constant
• principal sources of tidal force are the Sun and
Moon, which continuously change location
relative to each other and thus cause nutation in
Earth's axis
Barycenter
• refers to the point around which two
celestial bodies revolve
– Not usually at the center of an object
– Can be outside of the object (sun and Jupiter)
(a.) Two bodies of
similar mass orbiting
around a common
center of mass, or
barycenter.
(d.) Two bodies with
an extreme difference
in mass orbiting
around a common
barycenter (similar to
the Sun-Earth
system)
(b.) Two bodies with a
difference in mass
orbiting around a
common barycenter,
like the Charon-Pluto
system
(c.) Two bodies with a
major difference in
mass orbiting around
a common barycenter
(similar to the EarthMoon system)
Binary Star Systems
• There are four ways by which a binary star
system can be detected:
– visually, and are hence known as visual
binaries;
– spectroscopically, hence are known as
spectroscopic binaries;
– photometrically, these are known as eclipsing
binaries; and
– Astrometrically (wobbly stars), hence are
called astrometric binaries