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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The word “nebula” comes from Latin which means “cloud.” It is apt, because nebulae (the plural of nebula) look like clouds of gases. Nebulae are made up mostly of hydrogen and helium gases, plus plasma and dust. These clouds are believed to be the birthplace of stars.

There are many kinds of nebulae, often determined by the gases that make them up and how they appear to observers on earth. One type is the diffuse nebula, which has no definite shape and no definite outlines. Another type is the emission nebula, made up of plasma or ionized gas, and emitting multi-colored lights. An example of an emission nebula is the Eagle nebula. Yet another type is a planetary nebula, such as the Cat's Eye Nebula. This is thought to be composed of the shells of “dying” stars called white dwarves.

A very fascinating type of nebula is the dark nebula, an example of which is the Horsehead Nebula. This kind of nebula is extremely dense, with very thick clouds that block out the light behind them and stars in the background. Aside from those mentioned, some famous nebulae are the Crab Nebula or M-1, M-57 which is a Ring Nebula, the Cygnus Loop, and the Orion Nebula. These are fascinating objects in the sky that can be watched through a telescope.

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The Sun’s photosphere extends near its surface, in the region where the gas becomes opaque, with an optical depth of up to 400 kilometers. Despite the light emitted, the photosphere is one of the coolest regions in the Sun’s atmosphere with a temperature of about 6000 K. This region is also the densest part of the solar atmosphere but still incomparable to Earth’s atmosphere. At a closer look, the photosphere is comprised of convection cells known as granules, which are gas cells with a diameter of about 1000 kilometers with a life span of about eight minutes, following a continuous boiling pattern. This region in the solar atmosphere often appears as dark specks called sunspots, which is caused by the Sun’s magnetic field.

Other astronomical bodies have a photosphere like the Sun. This region in an astronomical body’s atmosphere is often the deepest, which is transparent for photons in different wavelength of the electromagnetic spectrum. The photosphere is a visual description of the Sun’s or another star’s surface.

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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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All galaxies are capable of emitting electromagnetic radiation. In fact, even the Earth’s galaxy, the Milky Way, produces radio waves. A radio galaxy, however, compared to ordinary galaxies gives off as much as a thousand to a million times more energy per unit time. Basically, elliptical galaxies produce more radio waves than spiral ones and, as such, are perceived as the brightest in galaxy clusters.

Radio waves are produced when electrons move at light’s speed through the magnetic field, a process called synchrotron radiation. Because of the field being influenced by magnetism, it bends the electrons’ path leading to their release of energy.

With the gadgets scientists now have, they can detect radio wave emissions from the most distant parts of the universe. Interestingly, such emissions were produced in the past when the galaxies were still one-third of their current age. This means that such galaxies are so distant that the waves have only now reached the Earth. The ability to measure electromagnetic radiation makes possible the detection of how far such galaxies are from the Earth as well as their speed.

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Recently, short-period comets have been subdivided into the Jupiter-type comets, like that of Temple 2 and Encke, which typically have periods of just twenty years; and the Halley-type comets, with intermediate periods of between twenty to about two hundred years.

Experts believed that the Jupiter-type comets are to have originated from the Kuiper Belt that surround the sun at various distances ranging from thirty to fifty astronomical units, or 7.5 billion kilometers to 4.7 billion kilometers. The outer planets Neptune and Uranus and their gravitational influences is thought to affect some objects within the Kuiper belt occasionally, causing them to be flung and be caught up in orbits which characterizes those belonging to the Jupiter family. Halley-type comets on the other hand, together with those considered to be long-period comets, appear to originate from the Oort cloud.

The life spans of short-period comets are influenced by the loss of gas, rocks and dust every time they swing in their orbits around the sun. Many are visibly split into many pieces, while some disintegrate or fall away. Comet’s lives are calculated to be around ten thousand years. But for the average short-period comet, it only takes two hundred trips for its entire lifetime. Based on every 76-year return of Halley’s Comet, experts calculated that it will only live for 15,200 years before it dies out.

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The second closest star is the Proxima Centauri discovered by Robert Innes. It is 30 trillion km away, making the sun 250,000 times nearer. Proxima Centauri (also called Alpha Centauri C) is one of the three stars (the other two being Alpha Centauri A and Alpha Centauri B) of the triple star system, the Alpha Centauri. The Alpha Centauri is part of the constellation Centaurus and is considered the third brightest star. The three stars of the Alpha Centauri are considered as one since they are also seen as one. Alpha Centauri A and B are too close to each other without any clear distinction between them and C is not visible at all.

Alpha Centauri A is a type of yellow star while B is a yellow orange one. The Proxima Centauri, on the other hand, is a type of red dwarf star, which means that it is small in size and of low temperature. Because of this, you cannot see it with the naked eye despite its being second closest star to the Earth. You will need to use the aid of a powerful telescope to view it.

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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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Comets

Periodic Comets are often written with a prefix, which is determined after the second perihelion passage and some of the comets in this category are still unnumbered. The letter P written after the number indicates that the comet is periodic. Some comets have the same name and the prefixes are the only clues to determine that their orbital periods are different. Most comets are named after the people who discovered them and others take the names of those who calculated the orbital periods that some of them engaged in a lifelong career of computing these values. Comets that are considered periodic have already appeared to some observers on Earth and are expected to appear again after completing their orbital periods. The perihelion passage of comets in this category can now be computed with high accuracy.

Some of the most popular periodic comets that have appeared before the eyes of many enthusiasts of the night sky include Halley, Encke, Tempel-Tuttle and Swift-Tuttle. Seeing a comet is a once in a lifetime experience and many night sly observers look forward to seeing one in their own time.

Halleys Comet – A Periodic Comet

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