Earth’s Place in the universe Chapter 21

Astronomy ( origin of modern astronomy)

• The golden age of astronomy was centered in Greece. The basic geometry ,trigonometry, which they developed, were used to measure the size and distances to the largest appearing bodies in the heavenly( the sun and the moon).

• 5th Century BC Greek Anaxogoras reasoned that moon shines by reflected sunlight because it is sphere. Only one half illuminated at one time.

• The early Greeks held incorrect geocentric view of the universe which profound the Earth was remained motionless at the center of the Universe.

• Sun and moon thought to be perfect crystal spheres.• Celestial sphere the stars were attached and

travelled daily around the earth. ( although it appears that the stars and planets move across the sky, this effect is caused by earth rotation on the axis.)

• The famous Greek Philosopher Aristotle concluded that Earth is spherical because it always cast a curved when it eclipses the moon.

A sun centered universe

• Aristarchus was the first to profess sun-centered heliocentric ( helios-sun,centric-center)

• He also used the simple geometric relations to calculate the relative distances of earth to the sun and the moon.

• He discovered the sun was many times more distant than moon and many times larger than Earth.

Measuring the Earth’s circumference.

• Eratosthenes was the first to attempt to established the size of the Earth.

• He observed the angle of noon day in 2 cities in Egyptian cities in North and South Alexandria and Syene. Finding the angle in noon day, sun differed by 7 degree or 1/50 of a complete circle.

Eratosthenes

• He concluded that circumference of the Earth is 50 times the distant of 2 cities.

• His calculation was 39,400km. The actual measurement was very close to the modern value 40,075 km.

Mapping the stars

• Hipparchus was best known for star catalogue.• He determined the location of 850 stars,

which he divided into 6 groups according to their brightness.

• He measured the length of the years to w/in minutes of the modern value and developed a method for predicting the times of lunar eclipse to w/in few hours.

Ptolemy’s model

• Ptolemy was credited w/developing a model of the universe that accounted for observable motions of the celestial bodies.

• According to Ptolemy.• He believed that the stars-studded celestial sphere

made a daily trip around motionless Earth. He proposed that Sun, Moon and Planets made a trip of various length along individual orbits. He likely to utilize something similar to this, to calculate the motion of the heaven.

Retrograde Backward Motion of Mars

• When viewed from Earth, Mars moves eastward among the stars each day, then periodically appears to stop and reverse direction. This apparent westward drift is a result of the fact that Earth has faster orbital speed than Mars overtakes. As this occurs, Mars appears to be moving backward.

Ptolemy

• Ptolemy proposed that planets orbited in small circle called epicycles. Revolving along circle deferent

d

epicycles

Earth

If Ptolemy’s theory was successful, why was it rejected?

• According to Ptolemy Earth-centered model, all heavenly bodies revolves around Earth. When Galileo used his crude telescope, he saw four moon revolving around Jupiter, He demonstrated that Earth was not the center of all motion.

The Birth of Modern Astronomy

• 1. Nicolaus Copernicus ( 1473-1543)• He was 1st great astronomer emerged after

Middle Age.• From Poland• He believed That Earth is a planet, just like

other planet. The daily motions of the Heaven. He reasoned and explained by it was a rotating Earth.

• Nicolaus Copernicus-• His work monumental work. De

REVOLUTIONIBUS ORIBIUM COELESTIUM ( on the Revolution of Heavenly Sphere).

• (Ptolemy objected his ideas.

Tycho Brahe

• Tycho was a Danish.• He persuaded King Frederick II to establish an

observatory where Tycho was head. ( lasted for 20 yrs)

• He observed planet Mars.• If the Earth orbits around the sun, the position of

nearby stars, when observed from 2 locations in Earth’s orbit. In six months apart, shift w/ respect to stars.

Tycho Brahe

• Tycho gave accurate measurement of planet Mars (w/ the use of instrument quadrant).

• He disagree with Copernicus.• Stellar Parallax- same as dominant eye.

Johannes Kepler

• Johannes Kepler-ushered in the astronomy with 3 laws of planetary motion.

• A) The path of each planet around the sun, while almost circular, is actually ellipse, with sun at one focus.

• B) Each planet revolves so that an imaginary line connecting it to the sun sweeps over equal intervals of time. ( if it is nearer to the sun, it moves faster, moves slowly farther from the sun)

• C) The orbital periods of the planets and their distances to the sun are proportional

Galileo Galilei

-He used new invention, the telescope to observe the sun and moon, planets more detail.

a) The discovery of Jupiter’s four largest satellites or moon.

b) The discovery that planets are circular disks rather than points of light.

c) The discovery that Venus appears as smallest planet when it is full phase and thus farthest from the sun.

Galileo ( cont.)

• D) The discovery that the sun ( the viewing of which can caused eye damaged that later blinded him) had sunspot dark region caused by slightly lower temperature. Heavenly bodies was found to have blemishes and rotational motion.

• E)The discovery that Moon’s surface is not smooth glass sphere. Galileo saw mountain, craters and plains indicating Moon and Earth were the same.( Plains are Sea of Tranquility, Sea of Storms)

• Galileo discoveries that the acceleration of falling object does not depend on weight.

• Galileo made this discovery by dropping balls of iron and wood from Leaning Tower of Pisa to show that they would fall together and hit the ground at the same time.

Sir Isaac Newton

• Newton was great genius ever existed quoted by his successor. He was the first one to formulate and test the law of universal gravitational, develop the law of motion and prove the force of gravity and combined with the tendency of an object to move straight line ( inertia) result in the elliptical orbits discovered by Kepler.

• He explained gravity as force that holds planets in orbit around the sun.

Newton• Law of universal gravitational force.• Everybody in the universe attracts every other body with a

force that is directly proportional to their masses and inversely proportion to the square of the distance between them.

• The law of gravitational also states that the greater the mass of object, the greater its gravitational force. Ex. The large mass of the Moon has gravitational force strong enough to cause ocean tides on Earth. Whereas the tiny mass of a communication satellite has very little effect on Earth.

Motion of Earth

• A)Rotation is the turning of a body on its axis. The solar day is the time interval from one noon to next 24 hours.

• B) Revolution is the motion of a body,such as a planet or moon along path around some point in space. Earth revolt around the sun in a elliptical orbit at the average speed of 107,000 km per hour.

• C) Axial precession- very slow movement of Earth.

Motion of the Earth-moom system.

• A) synodic month-the cycle of the moon through it phases requires 29 ½ days a time span.

• B) Sideral-apparent period of the moon’s revolution around Earth, and not true period , which takes 27 1/3 days.

Phases of moon regular cycle

• 1 Moon appear illuminated• 2) New moon position in the cycle as starting

point. After 2 days thin silver crescent appears.

• 3) Illuminated portion of the moon that is visible from Earth increasing to half circle, That can be seen noon to midnight).

Phases of moon regular cycle. ( cont).

• 4) Complete disk ( full moon phase) can be seen in rising in the east, sun sink in the west.

• 5) After 2 weeks, percentage of the moon can be seen steadily decline ( waning) Moon disappear, The cycle moon begins with reappearance of the crescent moon.

Eclipse of the sun and Moon

• A) solar eclipse- when the moon in a line directly between Earth and the Sun during new moon phase. It cast a dark shadow on Earth.

• B) Lunar eclipse-takes place when moon moves within the shadow of the Earth during full moon phase.