The Universe

THE UNIVERSE

The galaxy is included in the universe. It is a massive, gravitationally bound system that consists of stars and stellar remnants, an interstellar medium of gas and dust, an important but poorly understood component tentatively dubbed dark matter.

THE MILKY WAY

The milky way galaxy is the spiral galaxy which is known as home for other billons of star in the galaxy.. Like other spiral galaxies, the milky way has a bulge, a disk and a halo. Although all are parts of the same galaxy, each contain different objects. The halo and central bulge contain old stars and the disk is filled with gas, dust and young stars. The Milky Way Galaxy is at least 5 billion years older than the Sun.

Nebulae

A nebula is an interstellar cloud of dust, hydrogen gas, helium gas and plasma. In these regions the formations of gas, dust and other materials "clump" together to form larger masses, which attract further matter, and eventually will become big enough to form stars. The remaining materials are then believed to form planets, and other planetary system objects. Many nebulae form from the gravitational collapse of gas in the interstellar medium or ISM. As the material collapses under its own weight, massive stars may form in the center, and their ultraviolet radiation ionises the surrounding gas, which creates plasma, making it visible at optical wavelengths. An example of this type of nebula is the Rosette Nebula or the Pelican Nebula. The size of these nebulae, known as HII regions, varies depending on the size of the original cloud of gas, and the number of stars formed can vary too. As the sites of star formation, the formed stars are sometimes known as a young, loose cluster. Some nebulae are formed as the result of supernova explosions, the death throes of massive, short-lived stars. The material thrown off from the supernova explosion is ionized by the supernova remnant. One of the best examples of this is the Crab Nebula, in Taurus. It is the result of a recorded supernova, SN 1054, in the year 1054 and at the centre of the nebula is a neutron star, created during the explosion.

Supernova

A supernova (pl. supernovae) is a stellar explosion. Supernovae are extremely luminous and cause a burst of radiation that often briefly outshines an entire galaxy, before fading from view over several weeks or months. During this short interval, a supernova can radiate as much energy as the Sun could emit over its life span. The explosion expels much or all of a star's material at a velocity of up to a tenth the speed of light (30,000 km/s), driving a shock wave into the surrounding interstellar medium. This shock wave sweeps up an expanding shell of gas and dust called a supernova remnant.

The earliest recorded supernova, SN 185, was viewed by Chinese astronomers in 185 AD. The brightest recorded supernova was the SN 1006, which was described in detail by Chinese and Arab astronomers. The widely observed supernova SN 1054 produced the Crab Nebula. Supernovae SN 1572 and SN 1604, the last to be observed with the naked eye in the Milky Way galaxy, had notable effects on the development of astronomy in Europe because they were used to argue against the Aristotelian idea that the universe beyond the Moon and planets was immutable

 

Aurora

The Aurora Borealis shines above Bear Lake

 

Aurora Australis in Antarctica

 

Red and green Aurora in Fairbanks, Alaska

The phenomenon of aurora is an interaction between the Earth's magnetic field and solar wind. The aurora is a common occurrence in the Poles. It is occasionally seen in temperate latitudes, when a strong magnetic storm temporarily expands the auroral oval. Large magnetic storms are most common during the peak of the eleven-year sunspot cycle or during the three years after that peak. However, within the auroral zone the likelihood of an aurora occurring depends mostly on the slant of IMF lines (the slant is known as B_z), being greater with southward slants

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Short Quiz

1. The formation of Aurora is an interaction between _________and _____________.

2. Historically, galaxies are being categorized according to their apparent shapes, which are _____________, _____________ and_______________.

3. Milky Way Galaxy is approximately ___________ years older then the Sun.

Reference

http://en.wikipedia.org/wiki/Aurora_(astronomy)

http://en.wikipedia.org/wiki/Galaxy

http://en.wikipedia.org/wiki/Nebula

http://en.wikipedia.org/wiki/Milky_Way

Information prepared by Yien Peng.