OUR GALAXY AND UNIVERSE

History of the Universe

According to the prevailing scientific model Of The Universe, known as the Big Bang, the Universe expanded from an extremely hot, dense phase called the Planck epoch, in which all the matter and energy of the observable universe was concentrated.

The universe is composed of ordinary matter (5%) including atoms, stars, and galaxies, dark matter (25%)

which is a hypothetical particle that has not yet been detected, and dark

energy (70%), which is a kind of energy density that seemingly exists

even in completely empty space.

What is the Universe? The Universe is commonly defined as the totality of

existence, including planets, stars, galaxies, the contents of intergalactic space, and all matter and energy. Similar terms include the cosmos, the world and nature.

The observable universe is about 46 billion light years in radius. Scientific observation of the Universe has led to inferences of its earlier stages. These observations suggest that the Universe has been governed by the same physical laws and constants throughout most of its extent and history. The Big Bang theory is the prevailing cosmological model that describes the early development of the Universe, which is calculated to have begun 13.798 ± 0.037 billion years ago. Observations of a supernovae have shown that the Universe is expanding at an accelerating rate.

Components of the Universe

There are many components of the universe which includes solar systems, galaxies, countless numbers of stars , and so many other planets which we have never heard of. There are about 8 planets namely :- Mercury,Venus,Earth,Mars,Jupiter,Saturn,Uranus and Neptune. There are also some dwarf planets such as Ceres.

Picture of the Sun

Our Solar System

Did you Know???

1.The universe began with the Big Bang, and is estimated to be approximately 13.7 billion years old (plus or minus 130 million years).

2. The shape of the universe is influenced by the struggle between the pull of gravity (based on the density of the matter in the universe) and the rate of expansion. If the density of the universe exceeds a certain critical value, then the universe is "closed," like the surface of a sphere. 

3.The universe is overwhelmingly made up of things that cannot be seen. In fact, the stars, planets and galaxies that can be detected make up only 4 percent of the universe, according to astronomers. The other 96 percent is made up of substances that cannot be seen or easily comprehended. 

4. The planet Venus is has a temperature of over 500°C

CONSTELLATIONS

What is a constellation? A constellation is a group of stars that,

when seen from Earth, form a pattern. The stars in the sky are divided into 88 constellations.

The brightest constellation is Crux (the Southern Cross).

The constellation with the greatest number of visible stars in it is Centaurus (the Centaur - with 101 stars). The largest constellation is Hydra (The Water Snake) which extends over 3.158% of the sky.

Some more examples of some constellations

Ursa Major and Ursa Minor ORION SAGITTARIUS GEMINI

SOLAR SYSTEM:

The Solar System comprises of the Sun and its planetary system of eight planets,as well as a number of dwarf planets, satellites (moons), and other objects that orbit the Sun.

The eight planets:

1. Mercury2. Venus3. Earth 4. Mars5. Jupiter6. Saturn7. Uranus 8. Neptune Now the planet Pluto which was earlier

considered a planet is now classified as dwarf planet.

The Sun and the Moon Sun

The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields. It has a diameter of about 1,392,684 km (865,374 mi), around 109 times that of Earth, and its mass (1.989×1030 kilograms, approximately 330,000 times the mass of Earth) accounts for about 99.86% of the total mass of the Solar System. Chemically, about three quarters of the Sun's mass consists of hydrogen, while the rest is mostly helium. The Sun formed about 4.6 billion[a] years ago from the gravitational collapse of a region within a large molecular cloud.

                                 

Most of the matter gathered in the center, while the rest flattened into an orbiting disk that would become the Solar System. Once regarded by astronomers as a small and relatively insignificant star, the Sun is now thought to be brighter than about 85% of the stars in the Milky Way galaxy, most of which are red dwarfs. The absolute magnitude of the Sun is +4.83; however, as the star closest to Earth, the Sun is the brightest object in the sky with an apparent magnitude of −26.74.

Moon The Moon is the only natural satellite of the

Earth and the fifth largest moon in the Solar System. It is the largest natural satellite of a planet in the Solar System relative to the size of its primary, having 27% the diameter and 60% the density of Earth, resulting in 1⁄81 its mass. Among satellites with known densities, the Moon is the second densest, after Io, a satellite of Jupiter. It is the brightest object in the sky after the Sun, although its surface is actually dark, with a reflectance just slightly higher than that of worn asphalt.

Its prominence in the sky and its regular cycle of phases have, since ancient times, made the Moon an important cultural influence on language, calendars, art and mythology. The Moon's gravitational influence produces the ocean tides and the minute lengthening of the day. The Moon is thought to have formed nearly 4.5 billion years ago, not long after the Earth. Although there have been several hypotheses for its origin in the past, the current most widely accepted explanation is that the Moon formed from the debris left over after a giant impact between Earth and a Mars-sized body.

Eclipse

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he Moon

and Face

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he Moon

Eclipse An eclipse is an astronomical event that

occurs when an astronomical object is temporarily obscured, either by passing into the shadow of another body or by having another body pass between it and the viewer. An eclipse is a type of syzygy.

There are two types of eclipses :- Solar Eclipse Lunar Eclipse

Solar Eclipse As seen from the Earth, a solar eclipse

occurs when the Moon passes between the Sun and Earth, and the Moon fully or partially blocks the Sun. This can happen only at new moon, when the Sun and the Moon are in conjunction as seen from Earth in an alignment referred to as syzygy. In a total eclipse, the disk of the Sun is fully obscured by the Moon. In partial and annular eclipses only part of the Sun is obscured.

Lunar Eclipse A lunar eclipse occurs when the Moon passes

directly behind the Earth into its umbra (shadow). This can occur only when the Sun, Earth, and Moon are aligned exactly, or very closely so, with the Earth in the middle. Hence, a lunar eclipse can only occur the night of a full moon. The type and length of an eclipse depend upon the Moon's location relative to its orbital nodes. Unlike a solar eclipse, which can only be viewed from a certain relatively small area of the world, a lunar eclipse may be viewed from anywhere on the night side of the Earth.

Phases of the Moon As the moon circles the Earth, the shape of

the moon appears to change; this is because different amounts of the illuminated part of the moon are facing us. The shape varies from a full moon (when the Earth is between the sun and the moon) to a new moon (when the moon is between the sun and the Earth).

Definitions

Crescent Moon - When we can see only a sliver of the moon's disk (the side of the moon facing us) Full Moon - when the moon's disk is light because the Earth is between the sun and the moon .

Gibbous Moon - When we can see roughly three-quarters of the moon's disk .

Half Moon - (Also called quarter moon) when we can see one half of the moon's disk (this is one-quarter of the entire moon's surface) .

New Moon - When the moon's disk is dark (and invisible to us) because the moon is between the sun and the Earth Quarter Moon - (also called half moon) when we can see one half of the moon's disk (this is one-quarter of the entire moon's surface) .

Waning Moon - When the moon seems to be getting smaller, going from full to gibbous to half to crescent to new .

Waxing Moon - When the moon seems to be getting bigger, going from new to crescent to half to gibbous to full .

Our Galaxy

A galaxy is a massive, gravitationally bound system consisting of stars, stellar remnants, an interstellar medium of gas and dust, and dark matter, an important but poorly understood component. The word galaxy is derived from the Greek galaxias  ), literally "milky", a reference to the Milky Way. Examples of galaxies range from dwarfs with as few as ten million stars to giants with one hundred trillion  stars, each orbiting their galaxy's own center of mass.

Picture of our Galaxy