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Astronomy

Astronomy: Brief History of Astronomy Origin of the Universe and Solar System 

Universe – the vast gaseous space where galaxies, stars, planets, moons, and other heavenly bodies suspended and move with perfect orderliness

DEMOCRITUS - Pioneered the concept of milky way. Proposed that the Milky way was composed of thousands of unresolved star

PLATO - Viewed the universe as perfect and unchanging.He reasoned that the most perfect orbit of a planet would be circular and its motion is constant like the stars.

THALES - He believed that “everything comes out of water and that EARTH FLOATS ON WATER.

Celestial phenomena already known to astronomers of ancient civilizations. They already observed: 

  1. Solar eclipse

  2. Lunar Eclipse 

  3. Phases of the moon 

  4. Pattern and motion of the stars 

  5. Visibility of Planets

THE CELESTIAL SPHERE - In Ancient times, Earth was said to be enclosed in a rotating celestial sphere. It was proposed by Anaximenes, an Ancient Greek philosopher during 560 BCE. Here, he set stars as fixed points inside a solid vault (celestial sphere) The Ancient Greeks observe that the sun appears to move around the earth once a year counter clockwise along with the stationary path called ecliptic. As the sun moves along this path, it passes 12 constellations called zodiac.

Theories of the origin of the universe:

Big-bang Theory – by Edwin Hubble. He proposed that the primordial mass of the universe was once concentrated in an extremely hot and dense fireball called YLEM. It proposed that the universe is expanding.


Steady State Theory – that there is no beginning nor end to the universe. As galaxies recede due to expansion of the universe, new materials are constantly being produced in an empty space left behind.


Oscillating Universe Theory – Fred Hoyle proposed this theory after he discarded Steady State Theory, he proposed that the universe is expanding as in big-bang theory but its expansion would slow down and would eventually come to a halt because of mutual gravitational attraction.


Theories of the origin of solar system:

1. The Planetisimal Theory – sun collided with another star.


2. The Companion Star Theory – the sun has a companion

star that exploded when it collides with the sun.

3. The Nebular Hypothesis – the universe came from a

saucer shape nebula eventually cooled causing it to spin

in space.

Astronomy: Solar System and its Planets

Solar system – composed of the sun and all bodies that revolve around it

Two groups:

1. Composed of four solid planets – Mercury, Venus, Earth, Mars

2. Composed of gas planets – Jupiter, Saturn, Uranus, and Neptune

Sun

o Atmospheric Layers

  • Photosphere – light we see from the sun

  • Sunspot – black patches which can be seen during sunset

  • Chromosphere – the color sphere which gives pinkish color to the sun during solar eclipse

  • Corona – outermost layer of the suns atmosphere which,like the chromosphere, is only visible during solar eclipse

  • Reversing Layer – lowest layer of the sun’s atmosphere which absorbs solar wavelengths

Laws of planetary Motion:

  1. Ptelomaic System – earth is the center of the universe(Geocentric Universe)

  2. Copernican System – sun is the center of the universe(heliocentric Universe)


Johannes Kepler – formulated three laws concerning the

motion of planets (Kepler’s law):

  • The planet orbit the sun in elliptical paths

  • The closer a planet comes to the sun, the more rapidly it moves

  • The ratio of the cube of a planet’s mean distance from the sun to the square of its orbital period is constant

Astronomy: Motions of the Moon 

Moon – it is the earth’s satellite, its distance from earth is 384,000 km.

o Diameter: 1⁄4 of the earth’s

o Pull of gravity: 1/6 of the earth’s


Solar Eclipse – a partial/total hiding of the sun when the moon comes

between it and the earth

Lunar Eclipse – a partial or total hiding of the moon when the earth’s shadow is casted upon it


Apogee - is the point in the Moon's elliptical orbit when it is farthest from the Earth.

Perigee - is the point in the Moon's elliptical orbit when it is farthest from the Earth.


Synodic rotation - refers to the period it takes for the moon to complete one cycle of its phases as observed from Earth, which is approximately 29.5 days


Synodic month - is the period of time it takes for the Moon to complete one cycle of its phases, such as from new moon to new moon, as observed from Earth.


Sidereal rotation - is the time it takes for the moon to complete one full rotation on its axis relative to the fixed stars, which is slightly shorter at around 27.3 days


Phases of the Moon

New Moon - is the lunar phase when the Moon's illuminated side is facing away from the Earth, making the Moon appear dark and invisible in the sky. This is the only lunar phase where the Moon's unilluminated side is facing the Earth.


Waxing Crescent moon - is the first visible phase after a New Moon, where a small, thin, crescent-shaped portion of the moon's surface appears illuminated on the right side, gradually increasing in size over several days.


First Quarter - is the lunar phase when the Moon appears half-illuminated, as the Moon's position is shifted 90 degrees from the Sun, resulting in a distinct appearance compared to the other lunar phases.


Waxing Gibbous moon - is the lunar phase between a First Quarter and a Full Moon, where the moon's illuminated area is gradually increasing..


Full Moon - occurs when the Moon's illuminated side is fully visible from Earth, as the Moon is directly opposite the Sun in its orbit around the Earth.


Waning Gibbous moon - is the lunar phase after a Full Moon, when the illuminated portion of the moon is decreasing and appears more than half full.


Last Quarter moon - is the phase when the moon appears half-illuminated on the western side, as opposed to the First Quarter when it is illuminated on the eastern side.


Waning Crescent - is the phase of the moon just before the New Moon, where the illuminated portion is decreasing and less than half of the moon is visible from Earth.


Shadow

  • Umbra - the darkest portion of the shadow cast by an astronomical object during an eclipse, especially that cast on Earth during a solar eclipse

  • Penumbra - a partial outer shadow that is lighter than the darker inner shadow umbra, e.g. the area between complete darkness and complete light in an eclipse


Astronomy: Motions of the Earth 

Motions of Earth

  • DIURNAL MOTION - Refers to the apparent daily motion of the stars and other celestial bodies in the sky. It can be observed because the sun, moon, planets and stars rise in the east and set in the west. Due to Earth’s rotation

  • ANNUAL MOTION - Refers to the apparent shift in the location of the stars to the west, relative to the sun. It can be observed because the stars change position throughout the year. Due to Earth’s revolution around the sun (in an elliptical orbit).

  • PRECESSION - It was discovered by Hipparchus, a Greek astronomer. Refers to the westward motion of the equinoxes along the ecliptic relative to the fixed stars and opposite to the motion of the sun along the ecliptic. Annual gradual shift in the orientation of Earth’s axis. Earth requires approximately 26000 years to complete cycle of precession. 



Revolution – movement of the earth around the sun along its orbit

Rotation – rapid movement of earth around its own axis

23.5 degrees – tilt of the earth from the vertical


Equinox - refers to a day with an equal duration of day and night. We have two equinoxes in a year which are: 

  • Spring equinox on March 21 

  • Autumnal equinox on September 23 


Solstice - refers to a day with either the longest day or the shortest. The two solstices in a year are: 

  • Winter solstice on December 22 

  • Summer solstice on June 21



Astronomy: Other Celestial Bodies in Space

Galaxies – groups of billions of star and their planets, gases and dusts held together by gravity


Stars – mostly composed of 72% hydrogen, 25% helium and 3% other

materials (carbon, iron, nickel)


Incredible space Objects

Neutron star – very dense compact mass of neutrons; star which

collapsed under its own gravity


Black holes – areas in space with strong gravitational pull that no

matter or energy can escape from it


Asteroid - an irregularly shaped rock that orbits the Sun, mostly occurring in

a band asteroid belt between the orbits of Mars and Jupiter


Comet - an astronomical object that is composed of a mass of ice and dust and has a long luminous tail produced by vaporization when its orbit passes

close to the Sun


Meteor - a mass of rock from space that burns up after entering the Earth's atmosphere


Meteorite - a piece of rock that has reached Earth from outer space


Meteoroids - a mass of rock in space, often a remnant of a comet, that becomes a meteor when it enters the Earth's atmosphere and a meteorite when it falls to Earth