Transcript Astronomy

The First Science
Ancient Astronomy
First observed and used by cultures like the Chinese,
Egyptians, and Babylonians
• Used for planting crops, tracking hunting migrations
• Used to track the Sun, Moon, and the 5 known planets.
• Chinese tracked Halley’s comet for 10 centuries. Also
observed and recorded “guest stars”. We know these as
normal stars, which are usually too faint to be visible, which
increases its brightness as it explosively ejects gases from its
surface, a phenomenon we call a nova or supernova (novus =
new).
Golden Age of Astronomy
Occurred in Greece from 600 BC – 150 AD
Used Geometry and Trigonometry to
measure the distances between as well as
the size of the Sun and Moon.
• The Greeks created both geometry and
trigonometry!
Geocentric Model
Geo = Earth
Centric = center
Stated that Earth was a motionless sphere
at the center of the universe in which
everything else orbited.
• Earth’s rotation not demonstrated until 1851.
Ptolemy’s Model
Created in 141 AD.
Was a model that accounted for observable motions
of celestial bodies.
Noticed planets had a retrograde motion and
accounted for it with this model.
• Results from the combination of the motion of the Earth and
the planet’s own motion around the sun.
• Mars looked like it went backwards because Earth orbits the
Sun faster than Mars.
Ptolemy’s Model (cont.)
Used circular orbits around the Earth with
smaller circular orbits following them called
epicycles.
One step forward, two steps back…
Much of the accumulated
knowledge of astronomy was lost
around the 4th century during the
fall of the Roman Empire when
libraries were burned and
destroyed.
Saving Science!!
After the decline of Greek and Roman
civilizations the center of the study of
astronomy moved to the Middle East.
Specifically Baghdad.
• Ptolemy’s model had been translated into Arabic.
• Arabic astronomers expanded the then current star
catalog and divided the sky into 48 constellations.
• Became the foundation of our present day constellation
system.
• Ptolemy’s model had been
translated into Arabic.
• Arabic astronomers expanded the
then current star catalog and divided
the sky into 48 constellations.
• Became the foundation of our present
day constellation system.
• Ptolemy’s model not reintroduced into Europe until the 18th century.
Modern Astronomy
Break from philosophical and religious
views.
Took almost 13 centuries after Ptolemy to
make any major advances in astronomy in
Europe.
5 major scientists contributed to what we
know about astronomy.
Nicolaus Copernicus
(1473-1543) Poland
The idea of Earth being a sphere was
lost.
Convinced that Earth was a planet, just
like the other 5 then known planets.
Daily motions of celestial bodies
explained more simply by a rotation
Earth.
Nicolaus Copernicus (cont.)
Constructed the Heliocentric model.
• Helio = Sun (Greek)
• Centric = center
Still used circular orbits and smaller
epicycles like Ptolemy.
~~Follower Giordano Bruno was burned at the stake in
1600 for refusing to denounce Copernican theory.
Tycho Brahe
(1546-1601) Danish
Had an observatory near Copenhagen,
Denmark where he used pointers to measure
locations of celestial bodies for 20 years.
• Didn’t use telescopes because he didn’t have one! No
one did…..
Tried to disprove Copernicus using stars.
• Couldn’t observe the apparent shift shown with
rotation
• The apparent shift of stars is called stellar parallax,
which is used to measure distances between stars.
Johannes Kepler
(1571-1630) Czech Republic
Created 3 laws of planetary motion (16091619).
• He used these to account for the motion of Mars.
• Led him to find that the orbit of Mars is elliptical
not circular and its speed varies based on its
location during its orbit.
Kepler’s First Law of Planetary Motion
The path of each planet around the Sun, while
almost circular, is actually an ellipse, with the Sun
at one focus.
Kepler’s Second Law of Planetary
Motion
Each planet revolves so that an imaginary line
connecting it to the Sun sweeps over equal areas in
equal
intervals of time.
This law or equal
areas geometrically
expresses the
variations in orbital
speeds of the planets.
Kepler’s Third Law of Planetary Motion
The orbital periods of the planets and the
distances to the Sun are proportional. The
orbital period is measured in Earth years,
and the planet’s distance to the Sun is
expressed in terms of Earth’s mean distance
to the Sun called the astronomical unit (AU)
(1 AU ≈ 150 millions or 93 million miles). The
planet’s orbital period squared is equal to
its mean solar distance cubed.
Johannes Kepler (cont.)
Kepler’s laws support Copernicus’
theory
•Still didn’t determine the forces that act to
produce planetary motion.
Galileo Galilei
(1564-1642) Italy
Supported Heliocentric model.
Used telescopes for astronomy after
hearing about a Dutch lens maker who had
devised a system of lenses to magnify
objects.
• He built many of his own and was able to magnify
x30
Galileo (cont.)
5 Major Discoveries
•1: Jupiter’s 4 largest satellites (moons).
•2: Planets are circular disks (like Earth) rather
than points of light.
•3: Venus exhibits phases like the moon showing
that is must orbit around the Sun, not Earth.
Galileo (cont.)
• 4: The moons surface is not smooth glassy sphere,
instead it has craters and plains (he thought plains
might be bodies of water)
• 5: The sun has sunspots which were areas of
darker regions caused by slightly lower
temperatures. These were also tracked and
estimated a rotational period of the Sun to just
under a month.
Sir Isaac Newton
(1642-1727) England
Formalized the concept of inertia, the first law of
motion.
Determined the force that keeps the planets from
going in a straight line out in to space; Gravity.
Formulated and tested the law of universal
gravitation.
• Everybody in the universe attracts every other body with a
force that is proportional to their masses and inversely
proportional to the square of the distance between them.
Earth’s Movement
Rotation = 1 day
Revolution = 1 year
Earth rotates as it revolves around the sun.
Earth’s orbit is an ellipse
Axial tilt is the reason for the seasons!!
Perihelion = Earth is closest to the sun.
• About 91 million miles away from sun.
• Northern Hemisphere pointed away from sun makes is our
winter (January)
Aphelion = Earth is furthest from the sun.
• About 95 million miles away from sun.
• Northern Hemisphere pointed towards the sun makes is
our summer (July)
Earth/Sun Relationships
Equinoxes and Solstices determined by the
circle of illumination.
Equinoxes
• 2 per year
• Vernal (spring) – March 20
• Autumnal (fall) – September 24
• 12 hours of day and night at every latitude.
Earth/Sun Relationships (cont.)
Solstices
2 per year
• Winter Solstice (Dec 22)
• Winter for northern hemisphere
• Northern hemisphere tilted away from sun
• Occurs during perihelion.
• Summer Solstice (Jun 22)
• Summer in northern hemisphere
• Northern hemisphere tilted towards the sun.
• Occurs during aphelion.
Earth/Sun/Moon Relationships
Tides – daily changes in the elevation of the
ocean surface.
• Easiest ocean movement to observe other than
waves.
• Were not explained until Sir Isaac Newton showed
that there is a mutual attractive force between
two bodies (ex: Earth and Moon)
Tides
Moon causes bulge of water on side
nearest the moon because of
gravitational forces.
•Creates a equal sized bulge on the opposite
side of the Earth.
•The Sun’s tide-generating effect is only
about 46% that of the moon.
Tides (cont.)
New and Full moons
• Sun and Moon are aligned and their forces are
added together.
• The combined gravity causes higher high tides
and lower low tides.
These are called Spring tides.
Tides (cont.)
First and Third Quarter moon phases.
• Moon and Sun act on right angles and each
partially offset the influence of the other.
• Daily tidal range is less.
These are called Neap tides.