History of AstronomyHistory of

Astronomy

From Prehistoric Times to the Present Day

From Prehistoric Times to the Present Day

Periods of Astronomical Discovery

• Our picture of the universe has been assembled from ________________ of discoveries made by scientists from all part of the world.

• Prehistoric Period (Before 500 B.C.)• Classical Period (500 B.C. – 1400 A.D.)• Renaissance (1400 – 1650)• Modern Period (1650 to Present)

Prehistoric Astronomy

• Astronomical observations are a part of every __________________

• Observations of the rising and setting _____, the changing patterns of the ____________, eclipses

• These observations uncovered a ___________ pattern – __________________________________

• These patterns could serve as timekeepers because they are _____________________

• Could help foretell future events

Stonehenge

What is its purpose

Prehistoric Astronomy

• The early astronomers had to rely on ____________________ observation

• The most direct link to our ancient ancestors come from studying the _____________________

The Celestial Sphere• Impossible to get a sense of the 3-

dimensional shape of the universe• We can treat the stars as if they were all the

same distance from Earth and that they lie on the inside of gigantic dome surrounding the Earth called the __________________ with the Earth at the very center

• This serves as a model even though it has no ___________________ reality

• This served as the first model of the heavens

Constellations

• An arrangement of the stars on the celestial sphere that seemed to resemble something from their everyday lives (mostly animals)

• Many have shapes that bear _____________ resemblance to their namesake

• The stars in a constellation have no ____________________ relationship to each other except their direction in the night sky

The Constellations

• Astronomers recognize _______ constellations

• These are a collection of stars that appear to form a pattern

The constellations

• Help divide the sky up into __________

• Stars are labeled within the constellation based upon their ______________________ magnitude

α – alpha is the ________________

β – beta is the next brightest

Orion – The Hunter

Ursa Major – The Great Bear

Cassiopeia – The Queen

Constellations

• All stars move, but their positions as seen from Earth change so ____________ that it takes tens of thousands of years to notice any shift at all

• Ancient people used the rising sun and what ____________________ was present in that portion of the sky to predict _____________ and to __________________

Constellations

• If the sun rose in the constellations Pisces and Aquarius ______ travel was dangerous because they appear in the eastern sky when the stormy winter season is upon us.

• Harvest time is when the sun appears in the constellation __________

Motions of the Sun and Stars

• ________________ or Diurnal motion• Stars rise in the __________ and set in the

_____________ just like the Sun• Could be explained by the rotation of the

celestial sphere around us• Was easier for the ancient people to believe

this than that the earth wasn’t moving

Motions of the Sun and Stars• If we look at the spinning

celestial sphere there are two points that don’t move, the ____________________

• The north celestial pole marks the direction of _____________ north

• Helps to locate stars in the sky just like N & S on regular maps

• Celestial _____________ lies directly above Earth’s equator, another useful reference pt.

Motions of the Sun and Stars

• Earth’s orbit around the sun also changes the motion of the Sun and stars across the sky

• This motion is ____________________ and harder to observe so records need to be kept of these observations

• These motions repeat on an annual basis and are called __________________ motions

• The stars move in a tilted line with respect to the horizon which is 90° minus your latitude

Motions of the Sun and Stars• Annual Motion• New constellations appear in the eastern sky and

other disappear in the west• Allowed for a means to measure the passage of

time and the coming and going of seasons• Caused by the Earth’s motion about the sun• The stars that we can’t see are still there, we just

can’t see them through the _________________• A given star rises ________________________

earlier each night – If we add that up over a full year we get just about 24 hours.

The Ecliptic

• The path that the sun traces out on the celestial sphere and it is merely an extension of the Earth’s orbit

• This path is tilted with respect to the Earth’s axis by _______________°

• The name comes from eclipse because when a new or full moon would cross this line an eclipse takes place

The Ecliptic

• In reality it is the Earth’s axis that is tilted and gives us the seasons we experience

Solstices and Equinoxes

• For half of the year the sun rises _________ of due east and for the other half of the year it rises _______________ of due east (and likewise sets the same way in the west)

• In the Northern Hemisphere in the summer the sun rises in the northeast and sets in the northwest. What happens in the winter?

Solstices and Equinoxes• Spring and Fall begin when the sun crosses the

______________________; this is the ___________________ where day and night are of equal length

• Spring or vernal equinox is about _____________• Fall or autumnal equinox is about _____________• At this point the sun will rise due east and set due

west• Summer and winter begin when the sun stops its

northern or southern trek and reverses direction• These are called the _______________________• Summer solstice is around ____________ and the

winter solstice is around ____________________

Solstices and Equinoxes

• Buildings were also aligned to coincide with astronomical events

• Mayan pyramids allowed them to devise a very precise and complex calendar based on the movements of the planet _____________

The Planets and the Zodiac

• Greeks gave the name planets to those heavenly bodies that didn’t move in the same way that the other stars did

• The planets appear to move because of Earth’s orbiting of the Sun and their own orbits around the Sun

• Planets moved within a very narrow band on the celestial sphere called the ___________

• ___ constellations are within this narrow band

Signs of the Zodiac

The Planets and the Zodiac

• Planets appear to move ________________ against the stars

• However, they rise in the east and set in the west. Why the difference in apparent motion?

• Sometimes the pattern is interrupted and the planets move in the opposite direction of that expected.

• This is called ___________________ motion

Retrograde Motion

The Moon

• Rises in the __________ and sets in the _______________

• Lunar phases take place over a months time

• Origin of the ___________________

• What causes the phases?

Eclipses

• ___________: when one planetary body passes through the shadow of another

• ___________: part of the shadow where sunlight is completely blocked

• ___________: part of the shadow where sunlight is only partially blocked

Solar Eclipses• When the ____________ is between the sun

and the earth• Shadow of the __________ falls on the earth• If within the umbra we see a total solar

eclipse – never lasts more than _____ minutes

• Outside the umbra we see a ________ solar eclipse

• ____________ solar eclipse: when the shadow doesn’t reach earth – moon is near apogee (furthest from Earth) – thin ring of sunlight visible around the outer edge of the moon

Lunar Eclipses

• ____________ is between the moon and the sun• Total lunar eclipse: moon passes into earth’s

umbra• Partial lunar eclipse: moon passes through only

part of the umbra• Penumbral eclipse: when the moon passes only

through the earth’s penumbra – moon darkens only slightly

• Must be a _____________ moon

Eclipse Frequency

• Lunar eclipses are seen by more people – visible anywhere on the dark side of the earth

• Solar eclipses seen only by those people where the small shadow of the moon is cast

• Occur almost ______________ as often

Eclipse Frequency

• Orbit of the moon tilted 5º to plane of the earth and the sun – moon is usually above or below the plane of the earth’s orbit

• 2X each year the moon crosses the plane of the earth’s orbit

• Usually no eclipse happens when the moon crosses the plane of the earth’s orbit. Why?