Transcript THE UNIVERSE

THE UNIVERSE
SUB-PART SOLAR SYSTEM
• A VERY SMALL PART – THE UNIVERSE
MAY NOT BE INFINANT
SOLAR SYSTEM
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Sun at center
8 planets
Planets move in ellipses
Plane of rotation not same as plane of
revolution
• Mathematically highly predictable
• Formed from space trash ~4.6 by ago
Why do (did) we need to
know this stuff??
• To learn this required extensive
expenditure of time, energy, and effort
An answer -- maybe
• There certainty is no practical reason – at
least not yet.
• An answer might be – human nature and
the desire to ‘know’.
• There are some interesting philosophical
questions in these thoughts.
Let’s take a look at the practical
things that a early Homo might
need to know
One
• Living in an equatorial region and huntinggathering or early agriculture
– No winter or summer seasons
– There may be wet or dry seasons, however,
along with plant changes and migration of
selected animals
Two
• Living in a non-equatorial region and
hunting-gathering or early agriculture
– Climate
– Seasons
– Timing
Three
• What clues to changes and coming
events—remember no one has a clock or
a calendar until later on
• Astronomical clues
– Phases of moon
– Position of stars
– Location of sun
• BUT…..
• There is no need to know why.
• Then, why did Homo go looking for
answers??
I don’t know…
What, then, are the
tools for knowing
astronomical things?
Eyesight and counting
• i.e. how may days has it been since the
moon was full (or new)?
• What is the night-time pattern of stars? Is
it the ‘’winter’ pattern? How many ‘moons’
has it been since the appearance of the
‘winter’ pattern?
• Has the sun set (risen) in the ‘winter’ notch
(in yon mountains) yet?
• Note, questions like “How long are the
days?” doesn’t work—no clocks.
• But—are there lights in the sky that are not
always in the same spot? Can they be
used to tell seasons?
Devices for measuring angles
• The sextant, for example, and navigation
• Surveying instruments
Mathematics
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Along with the understanding of physics
triangulation
Parallax
Inverse square law
triangulation
parallax
Inverse square law-1
• Applies to any energy radiated from a
point – spherical radiation
• Example – the radiant energy received by
Venus compared to Earth; Earth = 1 AU,
Venus = 0.72 AU
• 0.72 = 1/1.39; invert and square (1.39)2;
= 1.9 times more energy
Inverse square law-2
• Energy received by Mars as compared to
Earth; Earth = 1 AU, Mars = 1.52 AU
• 1.52 = 1/0.66; invert and square; (0.66)2
= 0.44 (or 44% as much)
Inverse square law-3
• Double the distance; the energy
decreases to 1/4th
• Triple the distance; the energy decreases
to 1/9th
• Take 1/2 the distance; the energy
increases by 4
• Take 1/3 the distance and the energy
increases by 9
What, then, about Venus
• Near same mass as Earth – so has much
the same mass and composition of
atmosphere; never converted CO2 to O2
because
• much hotter! ~2x; and this conversion
required plant life
What, then, about Mars
• Considerably less massive than Earth
~1/9
• Hence unable to hold much of the lighter
gasses
• Cold, thin atmosphere
Telescope
• First ~1608
• Galileo heard about and made several
about 1610; published observations and
numerous discoveries; magnification ~30x
• After some fumbling around – leads to
Solar System as we know it.
Kepler’s laws of Planetary motion
• 1619
• Observed mathematical relationships
– Ellipse
– Equal areas
– Periods and axes
1687-Principia
• Newton’s laws of motion
• Newton’s law of gravitation
• A new mathematics invented
Newton’s first law - I
• “Every body continues in a state of rest, or
of uniform motion in a straight line, unless
it is compelled to change that state by
forces impressed upon it.”
• Objects in motion remain in motion and
objects at rest remain at rest, unless they
are acted upon by an outside force.
II
• “The change in motion is proportional to
the force impressed…..”
III
• “To every action there is always an equal
and opposite reaction…”
Newton’s law of gravitation
• F = G (m1m2)/d2
Photometry
• ~1900 with development of photography
• Use of photographs was first step to
instrumental collection of data
– Brightness (magnitude)
– spectrometry
spectrometry
• ~1815 with discovery of Fraunhofer lines
in spectra of sun
• The stars send us information—all we
need to do is learn how to interpret it.
Spectra (continuous)
How atoms affect light
Fe in the sun
Telescopes of ‘other’ wavelengths
• Radio telescopes 1932
• Other wavelengths
• Radar (~1950)
The Hubble telescope
• Outside Earth’s atmosphere
• Hence unaffected by atmospheric gases,
dust, and light
• ~1985