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General Overview
What is Astronomy?
Astronomy is a fundamental science which tries to quench our
thirst for very basic questions like What are we and where are we.
It is the study of the entire universe and Universe is the totality
of all space, time, matter and energy. Hence, in general Astronomy
is science of everything.
Why study astronomy (Its importance and usefulness)
Day (Earths rotation)
Month (Moons revolution around earth)
Year (Earths revolution around Sun)
Time
Calendar
Religion Artificial satellites (communication)
Physics, Chemistry, Geology, Geophysics, Biology etc.
Event predictions (e.g eclipse, meteor shower etc)
Celestial navigation -- ones position on earth (used in
military, commercial airplanes, and ships)
Why study astronomy (Cont.) (Its importance and usefulness)
Resources
Modern Technology
Sun-Earth Connection
Seasons, Tides, Animal behavior
Imagination
Are we alone in the Universe (SETI)
Human curiosities (intellectual satisfaction)
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From Here to
Infinity
Speed of Light is 300,000 km/sec or
186,000 miles/sec (the fastest speed known).
The light from the Sun reaches to the
Earth in about 8 min., and to Pluto in
about 5 hours 30 min.
The nearest star Proxima Centauri is
about 4.2 light years away.
The diameter of the Milky Way Galaxy
is about 100,000 light years.
Chapter 1
Discovering the
Night Sky
Sun rises in the east and sets in the west.
Moon, planets and stars also rise in the east
and set in the west.
The cycle of day and night goes on with the
rising and setting of the Sun.
Seasons change throughout the year.
Constellations change throughout the year.
In our day to day life we observe the
following cycles:
Earths Motions
Rotation Revolution
Spins on its axis
(24 hours)
Orbits around Sun
(365.25 days)
Day to day changes
(e.g. formation of day
and night)
Seasonal changes
(e.g. winters and
summers)
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Cycle of Day and Night
N
S
23
S
N
Formation of Seasons
Earths orbital motion
Tilt of Earths
axis to the ecliptic
Winter in N
Summer in S Summer in N
Winter in S
Subsolar point: The location on the Earth where the
Sun rays come directly, at an angle of 90 is called the
subsolar point.
Seasons Vernal/Spring equinox (March 21): Sun crosses the
celestial equator moving north. (Equal day & night on the
entire Earth.)
Summer solstice (June 21): Sun is at its northernmost point. The
longest day in the Northern hemisphere. 24 hours of daylight in the
Arctic regions near the North Pole, and 24 hours of night in the
Antarctic regions near the South Pole.
Autumnal/Fall equinox (Sept 21): Sun moves into the Southern
Hemisphere.
(Equal day & night on the entire Earth.)
Winter solstice (Dec 21): Sun is at its southernmost point. (The
shortest day in the Northern hemisphere. 24 hours of night in the
Arctic regions near the North Pole, and 24 hours of day in the
Antarctic regions near the South Pole.
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(Summer Solstice) (Winter Solstice)
Reading Reference
Tutorial on Sun-Earth relations and Seasons
outreach.as.utexas.edu/marykay/highschool/EarthSeason.doc
and
http://csep10.phys.utk.edu/astr161/lect/time/seasons.html
Video Geography Seasons
http://www.youtube.com/watch?v=taHTA7S_JGk
Lunar Phases The MOON shows different PHASES
FULL
GIBBOUS
HALF
CRESCENT
NEW
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Lunar phases:
full
3rd quarter(half)
1st quarter(half)
new
Waxing
Sunlight
Waning
Eclipse:
full
new
3rd quarter
1st quarter
No eclipse
is an event during which one body passes in
front of another, such that the light from the obscured
body is blocked.
Sunlight
Lunar Eclipse
Sunlight
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Total lunar eclipse
Lunar Eclipse
Sunlight
Penumbral lunar
eclipse
Partial lunar eclipse
Solar Eclipse
new
Sunlight
Total solar eclipse
(Umbra)
Partial solar eclipse
(Penumbra)
Annular solar eclipse
Solar Eclipse
(Picture from bartley.com)
Eclipse Geometry
Lunar orbit around
Earth is inclined by
about 5.2 degrees from
Earth's orbit around
Sun (ecliptic).
Favorable for eclipse
when line of nodes
(intersection of those
two planes) points at
the sun.
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Earth between Sun and Moon.
Only occurs at FULL MOON but
NOT each month.
Everyone (on night side of Earth) can see it.
Moon between Earth and Sun.
Only occur at NEW MOON but
NOT each month.
Only a small part of Earth can
see one at any given time
Lunar eclipse Solar eclipse
Eclipses
Eclipses
Annular Perfect alignment, but Moon too small to cover entire
Sun (near apogee).
Total Perfect alignment.
Moon big enough to cover Sun (near perigee). Lasts < 7.5
min.
Partial Moon only
covers up part of Sun
Partial In between
penumbra &
umbra
Total (Inside umbra) lasts not more than ~ 100 min.
penumbral
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