THE UNIVERSE

SUB-PART SOLAR SYSTEM

• A VERY SMALL PART – THE UNIVERSE MAY NOT BE INFINANT

SOLAR SYSTEM

• 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 hunting-gathering 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

• 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