A Nova is one event that happens repeatedly in the universe. This phenomena happens when a star comes to an end. As the light and heat capacity of stars wear throughout the years, it suddenly becomes pale white, thus getting the name “white dwarf”, due to the shrinking and dimming light power of the star. As time passes by, it then explodes, causing the star to burn out its remaining energy and become brighter than it ever was.

One example of this is the Supernova of 1054. This happened in China, when astronomers saw a star so bright that it was seen during the day. And since this occurrence was quite astonishing and odd, this event was recorded.

Books also say that a Nova is the smaller version of a supernova, since an event like this happens with a pair of stars, one which is a white dwarf and that of a cooler star. Since materials are being sucked off by the white dwarf, this causes the explosion of the star, though it may not be totally obliterated.

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A nebula or a “newborn star” appears like a cloud of gas and dust. More accurately, a nebula cloud is actually the birthplace of not just one but many stars. Nebulae (the plural of nebula) are mostly made up of hydrogen and other gases, and these determine the nebula’s appearance and, consequently, its classification or kind. There are emission nebulae, reflection nebulae, and even dark nebulae, to mention a few types.

The next phase in a star's life cycle is as a “regular” star––the kind seen normally in the nighttime skies, and of which the sun in our solar system is a good example. Our own sun is comparable to a teen-age star.

Millions of years later, a normal star will become a red giant, and then a red dwarf, and finally a white dwarf or a neutron star. A neutron star is much smaller than it used to be, like a drastically shrunken version of the original, but it is still very hot. The average neutron star is just about 1% the size of our sun, or as big as the earth, but its temperature can be something like 8,000 degrees Celsius. It is also much less bright than a regular star. Eventually, a neutron star cools and then fades. The whole process of a star’s “death” takes billions of years.

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Venus

Actually, the planet Mercury has the same behavior of being visible at dawn and at dusk. However, it can only be observed during a few weeks in a year. Since Venus is much larger and closer to earth, it has earned the title.

Because of its proximity to the sun, Venus is always found on the same side of the sky. If the sun is just setting to the west, the “star” can only be found at the west too. Its sulfuric acid clouds are highly reflective, causing it to glow brightly.

Venus is usually called the earth’s twin in terms of size, composition and gravitational pull. However, the atmosphere of the Evening Star is too hostile for life to exist. The atmospheric pressure on its surface is about 90 times greater than the earth’s. The air is also mostly carbon dioxide.

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After this, a main sequence star will continue emitting light and heat energy until it consumes all of its limited supply of hydrogen in its core. Then it will become redder, larger and luminous as it becomes a red giant star. At this stage, its outer envelopes will collapse and expand consuming nearby objects like planets, meteors and other heavenly objects.

It will continue to collapse its outer envelope and will even intensity its hotness is it exhausts the helium in its core, becoming a red super giant. It will eventually lose all of its mass and will leave a remnant of a hot core of carbon within a nebula of expelled gas. In some instances, the radiation from this hot core ionizes a nebula to produce a planetary nebula. But in most cases, the core of carbon cools down to become a white dwarf, a star that is relatively dim as compared to what it once was, a bright star and this ends its stellar evolution until it becomes black dwarf or a burned out star.

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Stars with 10 solar masses become red supergiants once they have used up their fuel source which is usually made up of hydrogen. Once this happens, the stars turn to other sources of fuel such as helium, which does not produce as much energy. As a result red supergiants have very cool surface temperatures that range from 3500-4500 K. As the star progresses on its evolution, it fuses heavier elements together until such a time when iron builds up in its core – this marks the life of a star that is at its very end. A red supergiant will take about a few hundred thousand years before it reaches this stage.

The largest known red supergiant is VY Canis Majoris, while the most popular is Betelgeuse. Betelgeuse belongs prominently in the constellation Orion and is part of the famous winter triangle seen in the night sky. This star is found to be about 370 times larger than the sun with a luminosity that is 10,000 times brighter.

Red Supergiant Star

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Currently there are seven main types of stars based on their temperature, O, B, A, F, G, K, M. Depending on their mass and stage of development however; stars may be classified as either dwarf stars or giants. Based on this grouping, scientists have found out that the most common stars in outer space are what they call red dwarf stars.

Red dwarf stars get their name because of their relatively smaller size and mass than the sun. These stars are known to have only a little less of the half of the weight of the sun. Their small size enables them to live for a very long time because they burn their fuel very slowly. However, because they burn only a little bit of fuel, red dwarf stars are also cooler compared to other stars and thus isn’t able to shine as brightly. Typically these stars only have a temperature below 4,000 K resulting in a faint light.

Though quite numerous in outer space, it will be very hard to see red dwarf stars in the night sky because of their small size and the faint glow that they give off. Probably the most popular red dwarf is the Proxima Centauri.

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You can think of a protostar as an immature star, starting its stellar (pertaining to stars) evolution. The development of a star begins with the nebula, a swirling cloud of interstellar (in between starts) gas and dust molecules. Because of the gravitational attraction that the molecules have, the nebula can unite into a denser, tightly packed object called a protostar through the process of accretion. The cloud becomes so dense that visible light inside it is blocked and cannot be seen.

As the protostar continues to gravitationally attract material and condenses into a more compacted form, the temperature and pressure at its center increases. When the inner temperature reaches about ten million degrees Celsius or eighteen million degrees Fahrenheit, nuclear reaction at the center of the protostar ensues. Before this occurs, the protostar is in a very unstable state. Atoms of hydrogen then bind together into helium, releasing a huge amount of energy that radiates outward as light and heat. This is the reason why stars are seen by people as being bright. At this stage, the star has attained a state of equilibrium.

This process of star formation takes approximately one hundred thousand years and even more to complete. The process of star formation is very dynamic with new stars born constantly. Learning about star formation fosters understanding of the vast and mysterious universe.

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Spectral class or spectral classification is the manner of organization in astronomy that deals with classifying stars according to brightness or luminosity, or through the spectrum or color of the star’s chromospheres.

In learning how to classify stars, the best way to check is through color. In this classification, there are different levels of a star’s chromospheres colors. This is none other than the Blue, Blue-White, White, Yellow-White, Yellow, Orange and Red. This is known as the O, B, A, F, G, K, and M classes. Furthermore, a certain star’s color determines its age. When the star has a blue hue, it clearly means that the star is still young. The oldest and most probably dying star is the M or red colored stars. To better easily understand the color levels, it is usually interpreted as “Oh, Be A Fine Guy/Girl, and Kiss Me”. Adding on this, the levels also determine how hot and bright the star is, with blue as the hottest and red as the coolest and dimmest of all stars.

This type of classification may be old, but it is the basic of other stellar classifications used. The current system used is the Morgan-Keenan System, which classifies a star also by spectrum type, though it is based on a 0 to 9 scale.

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Not all stars get to bow off in a fantastic display of planetary nebulae. Only those that are of low to medium mass—like our very own Sun—can create this type of spectacle when they die. Planetary nebulae don’t really last long compared to all other astronomical objects, but long enough to span a thousand generations of human life.

So, how does a planetary nebula form? It begins when the start reaches its Mira stage or that stage in its life when it turns into a pulsating red giant. The gradually increasing instability of this dying star eventually leads to its outer layer being expelled by the combined forces of strong stellar winds and the star’s own pulsations. The hot, but dead stellar core that is left behind emits ultraviolet radiations that cause the expelled outer layers of the star to radiate, thus forming a planetary nebula.

Planetary nebulae hold a very important role in the evolution of the universe. As they merge back into the interstellar space, they hand out generous amounts of the heavy elements they contain (carbon, nitrogen and oxygen) to the formation of new stellar lives.

Planetary Nebula

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The speculation about this celestial body exists even long before. The existence of these systems was confirmed in 1994 when Robert O’ Dell and his co-workers from the Rice University, through the use of the Hubble Space Telescope examined newborn stars in Orion Nebula.

According to the theory, it requires at least ten million earth years for a planetary system to be fully established and planets to fully form, through the combining of gas and dust clumping or forming together as one. In 1999, a certain protoplanetary disk was found in the Taurus portion of the galaxy, and it seemed that 6 young planets are surrounded by space gas and dust, indicating a formation of a new star system. Apart from this, it was also concluded that since the said disk was near the solar system, it also means that another star system can form at any time, in between another star system as well.

Furthermore, the protoplanetary disk is said to have a mass of 0.01 to 0.1 solar mass according to results found on newborn planets or stars. On the contrary, the results gained a discrepancy since the mass of a certain star system varies according to cumulative planetary and star masses.

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