Ancient Astronomy Ancient Astronomy and History of and History of

AstronomyAstronomyPhysics 101Physics 101

Physical SciencePhysical Science

Dr. SwezDr. Swez

Prehistoric AstronomyPrehistoric Astronomypre 500 B.C.pre 500 B.C.

► Daily motions of Sun, moon, planets, Daily motions of Sun, moon, planets, starsstars

► ConstellationsConstellations► Annual motions of Sun, moon, planets, Annual motions of Sun, moon, planets,

starsstars► EclipsesEclipses► Phases of the moonPhases of the moon► Time keeping and navigationTime keeping and navigation

Prehistoric AstronomyPrehistoric Astronomy► Cyclicity Cyclicity ► Celestial sphere, poles, equatorCelestial sphere, poles, equator► ConstellationsConstellations► SeasonsSeasons► EclipticEcliptic► Planets, Planets, Retrograde motion of planetsRetrograde motion of planets► ZodiacZodiac► Solar and Lunar EclipsesSolar and Lunar Eclipses

Prehistoric Astronomy - CyclicityPrehistoric Astronomy - Cyclicity

►Rising and setting of the Sun, moonRising and setting of the Sun, moon►Phases of the moonPhases of the moon►Planets (wanderers) different from Planets (wanderers) different from

starsstars►Allowed time-keeping, predictionAllowed time-keeping, prediction►Eclipses predictedEclipses predicted►Recognized several thousand years Recognized several thousand years

agoago

Prehistoric Astronomy - CyclicityPrehistoric Astronomy - Cyclicity

►Ancient Structures built to track Ancient Structures built to track astronomical motions (for astronomical motions (for predictions?)predictions?)

►Stone circles, Standing stones, Stone circles, Standing stones, Stone rows, Barrows, Hillforts, Stone rows, Barrows, Hillforts, Settlements, Dolmens, Menhirs, Settlements, Dolmens, Menhirs, StonehengeStonehenge

►Date back about 4000 yearsDate back about 4000 years

Stonehenge – England (started 2800 BC)

http:/www.amherst.edu/~ermace/sth/sth.html

http:/www.amherst.edu/~ermace/sth/maps.html

Maps of Stonehenge

Where possibly did the stones come from? How was Stonehenge constructed?

The stones of Stonehenge didn’t have to be quarried; they simply could be carried off. Up to six feet in height and four tons, the approximately 80 original bluestones are mostly doleite spotted with milky feldsparWhy did they bring these stones 250 miles to build Stonehenge and why did they retain these stones throughout its structural history.

Ockham’s Razor – the simplest solution to a problem is most likely to be right

“Nature alone set up these standing stones in Wales’s Preseli Mountains, source of the first stones installed at Stonehenge—the bluestones. Local folklore attributes healing power to springs gushing from the hills, and some researchers speculate tht’s why the stones were moved 250 miles east. Stonehenge may have been a place of healing”.From National Geographic “Secrets of Stonehenge, June 2008 page 54”

No physical reality

Recognition of the earth’s rotational axis and tilt

Extension of axis ontoCelestial SphereExtension of earth’s equator onto

the Celestial Sphere

Invariant points

ConstellationsConstellations

►Constellations are not real!Constellations are not real!► Imaginary ordering of starsImaginary ordering of stars►Stars have no physical relation to Stars have no physical relation to

each othereach other►Form of mnemonic to help us order Form of mnemonic to help us order

the skythe sky►Navigational aidsNavigational aids►Time keeping Time keeping

Betelgeuse

Rigel

Procyon

Sirius

Orion

http://www.astro.wisc.edu/~dolan/constellations/

Star charts of Orion

Annual Motions

Path of the Sun throughthe constellations definesa circumference on the celestialsphere - The Ecliptic

This is also an extension of the Earth’s orbit

Planets move in a narrow bandknown as the ZodiacEcliptic is the centerline of the ZodiacEcliptic is inclined at 23.5 o

to the Celestial sphere

Planets generally show anwest to east motion across the night sky

Sometimes planets appear to move backwards relative to the Stars

Shape of Earth

Classical AstronomyClassical Astronomy500 B.C. to 1400 A.D.500 B.C. to 1400 A.D.

►MeasurementsMeasurements Shape of the Earth (Pythagoras, Aristotle, 384-Shape of the Earth (Pythagoras, Aristotle, 384-

322 BC)322 BC) Relative sizes and distances of Earth, Moon, Relative sizes and distances of Earth, Moon,

Sun (Aristarchus, ~300BC)Sun (Aristarchus, ~300BC) Size of the Earth (Eratosthenes, 276-195 BC)Size of the Earth (Eratosthenes, 276-195 BC)

►Geocentric (Earth-centered) Geocentric (Earth-centered) Theory of the UniverseTheory of the Universe Aristotle, Aristotle, PtolemyPtolemy

► Aristarchus advocated helocentric!Aristarchus advocated helocentric!

GeocentricityGeocentricity

► Aristotle proposed Aristotle proposed his Earth -centered his Earth -centered UniverseUniverse

► Earth or sublunary Earth or sublunary region at center, region at center, consisting of earth, consisting of earth, water, fire, airwater, fire, air

► Heavens were made Heavens were made of ether or of ether or quintessence. quintessence. Planets were in fixed Planets were in fixed spherical shellsspherical shells

GeocentricityGeocentricity

► Ptolemy and others Ptolemy and others adapted the adapted the Aristotlean Aristotlean cosmology to cosmology to account for account for movement of planets movement of planets and geometric and geometric measurementsmeasurements

► In the In the AlmagestAlmagest Ptolemy laid out his Ptolemy laid out his visionvision

Evidence for Geocentric Evidence for Geocentric SystemSystem

Stellar brightness does not vary Stellar brightness does not vary over the yearover the year

Earth close, star should be bright

Typical star

Earth far, star should be

fainter

Evidence for Geocentric Evidence for Geocentric SystemSystem

Star positions do not vary as the Earth Star positions do not vary as the Earth moves (stellar parallax is not observed)moves (stellar parallax is not observed)

The ancients didn’t know the stars are The ancients didn’t know the stars are too far away to easily see these thingstoo far away to easily see these things

The RenaissanceThe Renaissance1400 - 1650 A.D.1400 - 1650 A.D.

► Re-examination, revision, rejection of Re-examination, revision, rejection of existing modelsexisting models

► Heliocentric (Sun centered) Theory of Heliocentric (Sun centered) Theory of Universe Universe (Copernicus, Digges, Bruno)(Copernicus, Digges, Bruno)

► Data and Records Data and Records (Brahe, Kepler)(Brahe, Kepler)

► Laws Laws (Kepler)(Kepler)

► Telescope Telescope (Lippershey, Galileo)(Lippershey, Galileo)Tycho Brahe 1546 – 1601

Johannes Kepler 1571 - 1630

The heliocentric model provided a more elegant explanation for Retrograde Motion

Kepler’s use of Tycho’s data led to a convincing description of planetary motions….but it wasn’t until Galileo and Newton came along that we could explain why

Planets move in ellipticalorbits

Orbital Speeds vary

Johannes Kepler (1571 – 1630)

Kepler’s Third LawKepler’s Third Law

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2

R

tt is the period of the planet in earth years

R is the distance from the sun in AU *

AU stands for astronomical unit. The distance from the sun to the Earth (93 million miles) is 1 AU.

Question 1 (text). A rock lies in the asteroid belt 3 times as far from the sun as the earth. What is it’s orbital period?

Modern AstronomyModern Astronomy1650 A.D. - present day1650 A.D. - present day

► Physical laws that govern the Universe Physical laws that govern the Universe (Newton, Einstein)(Newton, Einstein)

► Mathematics used extensively and Mathematics used extensively and calculus developed calculus developed (Newton)(Newton)

► TechnologyTechnology powerful telescopespowerful telescopes non-visible light telescopes (e.g., x-ray, IR)non-visible light telescopes (e.g., x-ray, IR) space explorationspace exploration

► Stellar evolution, Early Universe (big bang)Stellar evolution, Early Universe (big bang)

Tip of the Day: (1) How sunrise to sunset is defined. Sunrise is time from just when the top of the sun clears the horizon to sunset when the last bit of sun disappears.

“Apparent Magnitude” was defined by Hipparachus in 150 BC. He devised a magnitude scale based on:

Magnitude Constellation Star

1 (Orion) Betelgeuse

2 Big Dipper various

6 stars just barely seen

However, he underestimated the magnitudes. Therefore, many very bright stars today have negative magnitudes.

Magnitude Difference is based on the idea that the difference between the magnitude of a first magnitude star to a 6th magnitude star is a factor of 100. Thus a 1st mag star is 100 times brighter than a 6th mag star. This represents a range of 5 so that 2.512 = the fifth root of 100. Thus the table hierarchy is the following.

Magnitude Difference of 1 is 2.512:1, 2 is 2.5122:1 or 6.31:1, 3 is 2.5123 = 15.85:1 etc.

(2) Astronomy Magazine Sept. 2002 issue defines the faintest naked eye star at 6.5 apparent magnitude.

Absolute Magnitude is defined as how bright a star would appear if it were of certain apparent magnitude but only 10 parsecs distance. A parsec is 3.26 light year.

2

Some Apparent Brightness Ranges

This page was copied from Nick Strobel's Astronomy Notes.

Go to his site at www.astronomynotes.com for

the updated and corrected version.

1. This page was copied from Nick Strobel's Astronomy Notes. Go to his site at www.astronomynotes.com for the updated and corrected version

Men and women have looked up at the sky and wondered about the things they see up there for as long as humans have lived on our Earth. Long ago, the Sun and Moon were mysterious objects that could be seen in the day and night. But the planets and stars were even more mysterious probably because they are so far away that we could only see them as points of light. Unlike the things on the Earth that we can study up close, handle, listen to, smell, and taste, the only thing ancient watchers of the sky had to learn about things in space was their eyes and imaginations. Only very recently in the history of humanity have astronomers been able to extend the reach of our eyes (and our imaginations!).

Galileo pioneered modern explorations in the early 1600's by using a device originally invented for naval operations to explore the heavens. The device he used, of course, was the telescope, an instrument used to gather and focus light. Our atmosphere prevents most of the electromagnetic radiation from reaching the ground, allowing just the visible band, parts of the radio band, and small fractions of the infrared and ultraviolet through. Our eyes can detect the visible (optical) band, so the early telescopes were all built to observe in that part of the electromagnetic spectrum. It wasn't until the 1930's that astronomers began observing with another part of the electromagnetic spectrum---the radio band. The development of space technology has enabled astronomers to put telescopes above the atmosphere and explore all of those places out there using the full range of the electromagnetic spectrum

1

How your perception may be fooled.

From Explorations An Introduction to Astronomy 3rd ed, Thomas Arny p 123

Both circles in the sky and the bottom circle look smaller than the circle on the horizon.

Indeed all the circles are the same size!

6

Basic Type of Telescopes

Basic Diagram of Schmidt-Cassegrain Technology

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The Horsehead Nebula in Orion. This image, approximately 1.5° across, was obtained with the UK Schmidt telescope at the Anglo-Australian Observatory.(Image Credit: David Malin, Anglo Australian Observatory/Royal Observatory

Edinburgh.)

For photography of large areas of the sky the primary mirror is made with spherical curvature and an aspheric `corrector plate' is placed at the top end of the telescope tube. There are three large Schmidt telescopes in the world with fields about 6° across (the Moon's apparent diameter in the sky is half a degree). The oldest of these is the Palomar Schmidt (not to be confused with the Palomar 200-inch) and the other two are the ESO Schmidt in Chile and the United Kingdom Schmidt in Australia. These have been used to produce photographic charts of the whole sky.

The Schmidt Telescope

11a

10-meter Keck Telescope at the W.M. Keck Observatory.

1. This page was copied from Nick Strobel's Astronomy Notes. Go to his site at www.astronomynotes.com for the updated and corrected version.

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“The Hubble Space Telescope orbits far above the distorting effects of the atmosphere, about 600 kilometers above the Earth. This perch gives astronomers with their clearest view ever, but it also prevents them from looking directly through the telescope. Instead, astronomers use Hubble's scientific instruments as their electronic eyes.” Upper Left: Closer View

Photo and text courtesy of http://hubble.nasa.gov/

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The outer two stars of the big dipper point to polaris, the north star as do the contour lines. Polaris is off the picture and to the upper right.