What do we see when we look up?
Light Pollution
What do we see when we look up?
The Moon
Points of light
Most are “fixed” stars
A few are “wandering” stars (=“planets”)
Transient objects
Are celestial objects stationary in
the sky?
or
do we observe them to move?
Daily E to W motion of everything
• Sun, moon and planets all trace a similar
path through the sky: rising in the East,
culminating (reaching their greatest height)
in the South, setting in the West going
round below the Northern horizon and
rising in the East again, once every 24
hours
Sun, Moon, Venus and Jupiter rising the East over Fire Fire
Sun, Moon, Venus, and Jupiter rising inin the East over IslandIsland
(6 minute intervals)
(6-min intervals)
Orion rising in the East
Orion rising in the East
Celestial objects setting in the West
Objects setting in the West
Let’s begin
by looking at
the Sun
Rotation of the
Sun
The movement of the Sun defines our
Earth “day.”
http://eee.uci.edu/clients/bjbecker/ExploringtheCosmos/lecture8.html
Daily E to W motion of the Sun
(Period of 1 day)
The movement of the Sun defines our
Earth “year”
Celestial
Sphere
Annual motion of the Sun W to E around the Ecliptic
Sun’s movement along the ecliptic
The Sun moves through the constellations of
the zodiac in about 12 months
http://www.geocities.com/astrologyzodiac
s/zodiaccharts.htm
Seasonal Positions - ecliptic rises
and falls during the year
The north-south motion of the Sun, shown
by its position at sunrise.
first day of summer (the first day of winter
Summer Solstice), (the Winter Solstice),
moved to the north (23 moved to the south
On the first day of spring / winter (23 1/2 degrees,
1/2 degrees, relative to
(the Vernal / Autumnal Equinox), relative to the
the Celestial Equator)
the Sun rises due (exactly) East Celestial Equator)
Angle of Sun at Solstice & Equinox
Solar Eclipse
The Moon
• Each day the Moon
rises in the east and
sets in the west
• The apparent motion
of the Moon, from night
to night (13 degrees,
or approximately 26
diameters) against the
background of stars
The Moon
• Takes 27.3 days for Moon
to complete one orbit
around the Earth - about
the same as the time
taken for it to complete
one rotation.
• This synchronous rotation
means that it always
shows the same face to
the Earth.
Phases of the
Moon
What causes
the phases of
the Moon?
• New Moon occurs when
• ___________________
Phases of the moon
• ___________________
• Full Moon occurs when
___________________
• ___________________
• Between New Moon and
Full Moon, the Moon's
phase is waxing as the
illuminated area we see
from Earth increases and
waning as the illuminated
area we see from Earth
decreases.
Moonth
–Period of revolution around the
Earth: 27.32166 days (sidereal
month)
–Period from new moon to new
moon: 29.5306 days (synodical
month)
Lunar Eclipse
Ancients saw patterns in the “fixed stars”
Both: www.ne.jp/asahi/stellar/scenes
Both: www.ne.jp/asahi/stellar/scenes
Big Dipper actually not a constellation. But part of the
constellation of the Great Bear (Ursa Major),
Ursa Major
Stars circle around the North Celestial Pole in
a counter-clockwise (westward) direction
View at the Celestial Pole
Panoramic view of stars setting on the western
horizon, as seen at the Equator, in Kenya.
Stars set at right angles to the On the right, stars
On the left, stars
horizon, as they all move parallel circle
circle clockwise
to the Celestial Equator, which counterclockwise
around the South
crosses the Horizon at right around the North
Celestial Pole
angles at the Equator. Celestial Pole
S W N
Solar System
Orbits of planets in our solar system
• Revolve around the
Sun in a
counterclockwise
direction when one
views them from the
north pole of the
celestial sphere
• Lie close to the ecliptic
plane
Path of moon and all Planets lie within
8 degrees of ecliptic
Planet Range north or south of Ecliptic
Sun 0 degrees
Moon 5 degrees
Mercury 7 degrees
Venus 8.5 degrees
Mars 3 degrees
Jupiter 1.5 degrees
Saturn 3 degrees
Movement along the ecliptic
Sun, Moon, Venus and Jupiter rising in the East over Fire Island
Sun, Moon, Venus, and Jupiter rising in the East over Fire Island
(6-min intervals)
(6 minute intervals)
Slow motions of the individual
“planets” in the Ecliptic
Different “period” for each planet (time to
return to same position relative to “fixed
stars”):
shortest longest
Mercury Venus Mars Jupiter Saturn
88 days 29 years
Seeing the Planets in the Sky
• Inferior planets
– “morning” and “evening stars”
– Transit across the Sun’s disc
• Superior planets
– Rise and set but seen throughout the evening
• Opposition - when one
celestial body is on the
opposite side of the sky
when viewed from a
particular place
• A planet is said to be "in
opposition" when it is in
opposition to the Sun as
seen from the Earth
Viewing Outer Planets
• months around opposition
best time to view Mars,
Jupiter, Saturn
• closest to the Earth so
appears as large as
possible
• visible almost all night
• rising around sunset
• culminating around
midnight
• setting around sunrise
Viewing Inner Planets
• Inner planets - inside the
Earth's orbit positions
as viewed from Earth are
never very far from the
Sun
• Two kinds of Elongations
• Eastern Elongation:
Planet in the evening sky
• Western Elongation:
Planet in the morning sky
Mercury & Venus as “evening - morning stars”
• When on left between positions
3 and 5 evening star (when
sun sets in the west)
• When on right between positions
6 and 2 morning star (before
sun rises in the east)
• Venus visible about 2 hours and
48 minutes on a given day
(either in the morning sky or the
evening sky)
• Mercury visible about 1 hour and
7 minutes on a given day
A rare event: transit of inferior planet
• At inferior conjunction,
inferior planet may
appear as a dark dot
moving across the
Sun’s disc
• Does not occur every
year because orbit of
inferior planet does not
lie exactly on plane of
orbit of Earth
Slow motions of the individual
“planets” in the Ecliptic:
“direct” and “retrograde” motions
Most of the time: W to E relative to fixed stars
(= “direct” motion)
Sometimes: E to W relative to fixed stars
(= “retrograde” motion)
They normally move east each night, but
sometimes they reverse for a time
http://www.geocities.com/astrologyzodiacs/zodiaccharts.htm
“Wanderers”
Jupiter and Saturn Pas de Deux
Retrograde Motion (3 years of Saturn’s orbit)
Early Astronomy
Stonehenge: an astronomical observatory
begun ~ 3000 years B.C.
Stonehenge as a observatory
At dawn of the summer solstice, the Sun’s rays
fall between the two “Heel stones” and
illuminate the Altar Stone
Left: http://www.english-heritage.org.uk/stonehengeinteractivemap/sites/stonehenge/08.html
Right: http://news.bbc.co.uk/1/hi/england/wiltshire/5098706.stm#map
Many cultures use a lunar calendar
The period between “new moons” defines a lunar month
For example:
• The Jewish calendar contains 12 months of 29-30 days
each (13 in a “Shanah Me'uberet” or a leap year).
• The first sighting of the crescent of a new moon ushers in
Eid-al-Fitr, the three-day feast that signals the end of
Ramadan, the Muslim month of fasting.
•The Western Christian Church celebrates Easter on the
1st Sunday after the 1st full moon after the Vernal Equinox
Sumerian Astronomy (~ 3000 B. C.)
Developed base-60 number
system (Do we ever use
base-60 numbers?
When?)
Made precise
measurements of the
locations and motions of
stars and planets, and
noted eclipses and other
events
… but they didn’t develop a
cosmological “model” of
the heavens
Greek Developments in Astronomy
The Pythagoreans (~500 B.C.)
- laid foundation for Geometry
and Trigonometry
Greek philosophers knew that:
- the Moon shines by reflected
light
- Earth was spherical (from shape
of Earth’s shadow during lunar
eclipses)
- Eratosthenes – determined the size
of Earth in 2nd c. B.C. from
observations & simple geometry
Top: http://www.wherry.com/photos/2004-10-27-lunar-eclipse/
Bottom: http://www.fes.uwaterloo.ca/crs/geog165/images/
eratosthenes.gif
I would like to thank Dr. Ted Georgian and
Dr. George Lapennas for the use of some of
their PowerPoint slides