Astronomy
Astronomy is the study of celestial objects, space, and the universe as a whole. It involves the observation and analysis of stars, planets, galaxies, and other astronomical phenomena, as well as the laws and theories that govern their behavior.
Astronomy is the study of universe and the celestial bodies, gas and dust within it. Astronomy includes observations and theories about solar system, the stars, the galaxies and the general structure of space.
 Universe:
The vast empty space around us that consists of stars, solar system, galaxies etc. is called universe.
It is defined as sum total of all matter and energy that exists or has excited both in space and time.
The totality of everything that exists, including all matter and energy , the planets, stars, galaxies and the contents of intergalactic space.
Astronomical system of Units:
Astronomical System of measurement developed for use in astronomy. It was adopted by the International Astronomical Union in 1976 and has been significantly updated in 1994 and 2009. The system was developed because of the difficulties in measuring and expressing astronomical data in International System of Units. The astronomical system of Units is a tri-dimensional system, in that it defines units of length, mass and time only.
Astronomical Unit of Time:
The astronomical unit of time is the day, defined as 86400 seconds. 365.25 days make up one Julian year. The symbol D is used in astronomy to refer to this unit.
Astronomical Unit of Mass:
The astronomical unit of mass is the solar mass. The solar mass 1.98892×1030 kg is a standard way to express mass in astronomy, used to describe the masses of other stars and galaxies. It is equal to the mass of the sun
Astronomical Unit o Length:
An astronomical unit is defined as the average distance between Earth and the Sun and it is approximately 150 million kilometers (93 million miles)/
Astronomical unit light year and parsec are the units for measuring huge distances
Light Year:
A light year is the distance that light can travel in one year in a vacuum, which is about 5.8×1012 Â miles or 63240 AU or 9.46053×1012 Â kilometers.
Persec:
A parsec is a unit of distance that is equal to 3.26 light year or 3.085678×1013 kilometers or 206265AU. It is the distance of which a star would have a parallax of 1 second of arc. It is commonly used to measure distances between stars and galaxies.
Astronomy: Origin of the Universe
The Big Bang Theory is the leading explanation about how the universe began. At its simplest, it talks about the universe as we know it starting with a small singularity, then inflating over the next 13.7 billion year to the cosmos that we know today. Because current instruments don’t allow astronomers to peer back at the universe’s birth, much of what we understand about the Big Bank Theory comes from mathematical theory and models.
Big Bang Theory:
Most astronomers believe the universe began in a Big Bang about 13.7 billion year ago. AT that time the entire universe was inside a bubble that was thousands of times smaller than a pinhead and it was named as singularity. It was hotter and denser than anything we can imagine. Then it suddenly exploded. The universe that we know was born. Time, space, and matter all began with the Big Bang.
In a fraction of second, the universe grew from smaller than a single atom to bigger than a galaxy. And it kept on growing at a fantastic rate. It is still expanding today. As the universe expanded and cooled, energy changed into particles of matter and antimatter. These two opposite types of particles largely destroyed each other. But some matter survived .More stable particles called protons and neutrons started for when the universe was one second old .Over the next three minutes, the temperature dropped below 1 billion degree Celsius. It was now cool enough for the protons and neutrons to come together forming hydrogen and helium nuclei.
After 300000 years, the universe had cooled to about 3000 degrees. Atomic nuclei could finally capture electrons to form atoms. The universe was filled with clouds of hydrogen and helium gas. These clouds of dust and gases formed all celestial bodies afterwards.
Evidence for the Big Bang:
By analyzing the spectrum of light from a star or galaxy, astronomers can tell how fast it is moving , and whether it is moving towards earth or away from earth. If an object is moving away from earth its light shifts to longer, redder wavelengths, and an effect known as red shift. If an object is moving towards earth its light shifts to shorter, blue wavelengths, an effect know as blue shift. Red shift supports the big bang theory.
The light from distant galaxies is red shifted ( this tells us the galaxies are moving away from us) and the further away the galaxy the greater the red shift ( this tells us that the more distant the galaxy the faster it is moving) a second piece of evidence that supports the big bang theory is cosmic background microwave radiation. Arno Penzieas and Wilson detected a cosmic microwave background radiation while studying radio signals. These radiations are received from all parts of the universe and are thought to be the heat left over from the original expansion or big bang.
Some of other theories argue that the Big Bang Theory based on a false premise. Some instead prefer to build theories on a static universe, which is what was originally predicted by Einstein’s theory of general relativity.
The ultimate fate of the Universe:
Once the notion that the universe started with a rapid expansion nicknamed the Big Bang became accepted by the majority of scientists, the ultimate fate of the universe became a valid cosmological question, one depending upon the physical properties of the mass/ energy in the universe, its average density, and the rate of expansion.
There is growing consensus among cosmologists that the universe is flat and will continue to expand forever. The ultimate fate of the universe is dependent on the shape of the universe and what role dark energy will play as the universe ages. Astronomers recognize for models of possible futures for the universe
Four Models of Future Universe
- Close model ( Constracting Universe Theory)
- Flat Model ( Steady State Theory)
- Cyclic Model ( Cyclic Universe Theory)
- Open Model ( Expanding Universe Theory)
Continue…………..