Physica Science: The Universe and the Solar System

Celestial Sphere

The Ancient Greeks considered Earth to be enclosed in hollow called the

North celestial pole and South Celestial Pole

The points where Earth’s rotational axis cuts the sphere.

Celestial equator

The projection of Earth’s equator in the celestial sphere.

Ecliptic

The path that the sun appears to take around the sphere. It is inclined 23.5 degrees with respect to the celestial equator.

Solstices

The two points on the ecliptic with the greatest distance from the celestial equator.

Equinoxes

The two points where the ecliptic intersects the celestial equator.

Thales of Miletus

600 BCE, proposed that Earth is a disk floating in water.

Anaximander

520 BCE, also from Miletus suggested that Earth is a cylinder and its surface is curved.

Geocentric Model

Considers Earth as the center of the universe.

Heliocentric Model

Assumes the Sun to be the center of the universe.

Pythagoras

was the first to assert that Earth is round, and that the heavenly bodies move in circles.

Pythagorean Model

Earth is at rest of the universe and everything rotates around it.

Plato’s Model

Adopted the Pythagorean Model and assumed that all motions in the universe are perfectly circular and that all heavenly bodies are ethereal or perfect.

Retrograde Motion

He said planets are moving from west to east. But occasionally, the backtrack for a while and it is called

Eudoxus’ Model

Referred to Plato’s Model, using a series of 27 concentric spheres on which the sun, the moon, and the planets moved in perfect circular motion.

the terrestrial and the celestial

He divided the universe into two realms, the ----- and the --------

Terrestrial

is below the moon’s orbit.

Ptolemy’s model

He used the idea of Epicycle.

Epicycle

is a circle on which planet moves.

deferent

The center of the epicycle in turn moves around Earth along a bigger circular path called the

Equant.

He defined a point on the other side of the deferent’s center and called it the

Nicolaus Copernicus

He asserted that Earth spins on its axis every day and revolves around the sun just like other planets; only the moon orbits Earth.

Stellar Parallax

is the apparant displacement of a star because of change in observer’s point of view.

Tycho Brahe

The last and greatest astronomer prior to the invention of the telescope.

Tycho Brahe

At the age of 30, he establish his own astronomical observatory located between Germany and Sweden.

Tycho Brahe’s Universe

in his model, the sun orbited Earth, while other planets orbited the sun.

Galileo Galilei

His invention of his own telescope helped him to observed things that contradicts the models of Ptolemy and Aristotle and supported the Copernican model.

sunspots

The surface of the sun has some blemishes, which are now called

four

Jupiter has------- moons revolving around it. This showed that not all heavenly bodies revolve around Earth.

Johannes Kepler

served as an assistant to Tycho Brahe. He inherited the numerous observational data on planetary motion when Tycho Brahe died. He was able to formulate his three laws of planetary motion with the use of these data.

Law of Ellipses

States that the planets move in ellipses having a common focus situated at the sun.

perihelion

The closest point to the sun in planet’s orbit is the

aphelion

the farthest point to the sun in planets orbit is the

Law of Equal areas

The planets move around the sun in such a way that a line drawn from the sun to the planet sweeps out equal areas in equal intervals of time.

Law of harmonies

It states that the squares of the periods of the planets are proportional to cubes of their distance from the sun is the same for every one of the planets.

Period

is the time it takes to make one complete revolution around the sun.