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Earth in Space
(a work in progress)
Dr. Alan F. Weekes
Astronomy
Possibly the oldest science
Contrast with astrology: belief system
The belief that the positions of the planets
and the sun at the time of your birth affects
your personality and your future.
Calendars
Seasons, festivals, time, flood of the Nile
Year
The time it takes for the sun to rise in the same
place
~365 ¼ days
Month
Roughly the time for the moon to go through its
set of phases
Some cultures exactly a month, from new moon
to new moon
Asian, Jewish, Moslem
29.5 days from new moon to new moon
• Day
– from sunrise to sunrise
– 24 hr.
• Week
– Named for visible moving objects in the sky
– Sun, Moon, Mercury, Venus, Mars, Jupiter, Saturn
– Sunday, Monday, Saturday
– Tiwe’s Day (Mars), Woden’s Day (Mercury), Thor’s Day
(Jupiter), Frige’s Day (Venus)
– lunes, martes, miercoles, jueves, viernes,
sabado, domingo
A Little History
Geocentric Theory
Earth is the center of the universe
• Everything revolves around the earth
• What is apparent, what is observed
• agrees with some religious views
Heliocentric Theory
Nicholas Copernicus
Sun: the center of the solar system
Copernicus (February 19, 1473 – May 24, 1543)
– Polish priest, astronomer
• Considered heretical, not published until his
death bed in 1543
– People were arrested, tortured and killed for
teaching this idea
– Galileo under house arrest for years
for this idea
Giordano Bruno
Galileo Galilei
Motions of the Earth
Revolution
Time it takes to revolve around another body, the sun.
Year
• 365.24 days for the Earth
• Leap years are determined according to the following rule:
– Every year that is exactly divisible by 4 is a leap year
– except for years that are exactly divisible by 100;
these centurial years are leap years only if they are exactly
divisible by 400.
Note: The Earth is held in its orbit by the Sun’s gravity.
Rotation
The time it takes for a body to rotate about
an axis
• Day
– 23 hr. 56 min. for the Earth
– Relative to distant objects
– 24 hr for sunrise to sunrise
– The earth has moved a bit in its orbit relative to
the sun, so it takes a little longer for the sun to
be visible
– ~1000 mph at the equator, 800 mph here
Other important characteristics
Size- diameter: 12,756.3 km (7,926 mi)
Orbit:
149,600,000 km (93,500,000 mi) from Sun
1.00 astronomical unit (au) from Sun
Elliptical, not circular
• More of a squashed circle
– Closest to the sun on Jan. 4, 147.5 million km
– Farthest from the sun July 4, 152.6 million km
Mass: 5.9972x1024 kg
Science 8
Video: Basic Astronomy
Goby Last
Per. ___ 9/13/13
5 Things new or interesting to you in the video.
1.
2.
3.
The Seasons
The earth is tilted in its orbit around the
sun at 23.5o
The earth is always tilted in the same
direction, North Star over the North Pole
• 23. 5o North Latitude- Tropic of Cancer
• 23. 5o South Latitude- Tropic of Capricorn
• 66.5o North Latitude- Arctic Circle
• 66.5o South Latitude- Antarctic Circle
Seasons are determined by where the
most direct rays of the sun are hitting
the Earth.
Animation
Old Farmer’s Almanac Site
Seasons of 2013:
SPRING EQUINOX
March 20, 7:02 A.M. EDT
SUMMER SOLSTICE
June 21, 1:04 A.M. EDT
FALL EQUINOX
September 22, 4:44 P.M. EDT
WINTER SOLSTICE
December 21, 12:11 P.M. EST
The Earth’s Moon
Earth’s companion in space
Large in relation to the Earth
• About ¼ diameter of Earth, approx. the size of
the U.S. from coast to coast
• Diameter: 3,476 km (2,172 mi)
Distance from Earth
• Orbit: 384,400 km (240,000 mi)
Mass: 7.35e22 kg
• Gravity, about 1/6 of Earth’s
Features of the Moon
Craters
Made by impacts with meteorites
Mare
“seas” made by the outpouring of lava
early in the moon’s history
Rays
Bright lines extending out from some
newer craters
The Moon’s Motions
• Rotation- about 27 1/3 days
• Revolution- about 27 1/3 days
– The moon keeps the same side toward the Earth as
it goes around the Earth
– The moon is held in its orbit by the gravitational
attraction between the Earth and the moon.
The Moon’s Phases
The geometry of the Earth- Moon- Sun determines
the phases of the moon
With the phases of the moon, we are seeing
different amounts of the lit portion of the moon.
½ of the moon is always illuminated by the sun.
The Moon’s Phases
The Moon’s Phases 2
Eclipses
Named after what goes dark.
Solar eclipse
Moon comes between the
Earth and the sun.
Occurs during a new moon.
Only a small area sees it
(totality).
Next one here,
August 21, 2017
Lunar Eclipse
The earth is between the moon and sun.
Full moon
Everyone on the night side of earth sees it.
Next here: October 18, 2013
Partial
The Tides
The tides in the ocean
are a result of the
gravitational attraction
of the moon and sun
on the earth.
There is always a
bulge of water facing
toward the moon
and one away from it.
When you are under a
bulge, you have high tide.
When you are between
bulges, you have low tide.
The sun also influences tides
The greatest range is at full and new moon, straight line, spring
tide.
The least range is at the quarter moons, right angle, neap tide.