What are they and how are they made?
A star is a massive, luminous ball of plasma that is held together by gravity. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth. Other stars are visible in the night sky, when they are not outshone by the Sun. Historically, the most prominent stars on the celestial sphere were grouped together into constellations, and the brightest stars gained proper names. Extensive catalogues of stars have been assembled by astronomers, which provide standardized star designations.
For most of its life, a star shines due to thermonuclear fusion in its core releasing energy that traverses the star's interior and then radiates into outer space. Almost all elements heavier than hydrogen and helium were created by fusion processes in stars. Astronomers can determine the mass, age, chemical composition and many other properties of a star by observing its spectrum, luminosity and motion through space. The total mass of a star is the principal determinant in its evolution and eventual fate. Other characteristics of a star are determined by its evolutionary history, including the diameter, rotation, movement and temperature. A plot of the temperature of many stars against their luminosities, known as a Hertzsprung-Russell diagram (H–R diagram), allows the age and evolutionary state of a star to be determined.
A star begins as a collapsing cloud of material composed primarily of hydrogen, along with helium and trace amounts of heavier elements. Once the stellar core is sufficiently dense, some of the hydrogen is steadily converted into helium through the process of nuclear fusion. The remainder of the star's interior carries energy away from the core through a combination of radiative and convective processes. The star's internal pressure prevents it from collapsing further under its own gravity. Once the hydrogen fuel at the core is exhausted, those stars having at least 0.4 times the mass of the Sun expand to become a red giant, in some cases fusing heavier elements at the core or in shells around the core. The star then evolves into a degenerate form, recycling a portion of the matter into the interstellar environment, where it will form a new generation of stars with a higher proportion of heavy elements.
Binary and multi-star systems consist of two or more stars that are gravitationally bound, and generally move around each other in stable orbits. When two such stars have a relatively close orbit, their gravitational interaction can have a significant impact on their evolution. Stars can form part of a much larger gravitationally bound structure, such as a cluster or a galaxy.
Famous Star Formations and Constellations
In astronomy, the Pleiades, or seven sisters, (Messier object 45) are an open star cluster in the constellation of Taurus. It is among the nearest star clusters to Earth and is the cluster most obvious to the naked eye in the night sky. Pleiades has several meanings in different cultures and traditions.The cluster is dominated by hot blue stars that have formed within the last 100 million years. Dust that forms a faint reflection nebulosity around the brightest stars was thought at first to be left over from the formation of the cluster (hence the alternate name Maia Nebula after the star Maia), but is now known to be an unrelated dust cloud in the interstellar medium that the stars are currently passing through. Astronomers estimate that the cluster will survive for about another 250 million years, after which it will disperse due to gravitational interactions with its galactic neighbourhood.
The above information was sourced from Wikipedia
The purpose of constellations is to tell us which stars are which, nothing more. Trying to identify stars is difficult but constellations help us to split the night sky up into manageable bits. One of the best known constellations is Orion. Orion is found on the celestial equator meaning that it is visible from the northern and southern hemispheres.
Orion includes the prominent asterism known as the Belt of Orion: three bright stars in a row (The Three Kings). Surrounding the belt at roughly similar distances are four bright stars, which are considered to represent the outline of the hunter's body. Apparently descending from the 'belt' is a smaller line of three stars (one of which is in fact not a star but the Orion Nebula), known as the hunter's 'sword'. In artistic renderings, the surrounding constellations are sometimes related to Orion: he is depicted standing next to the river Eridanus with his two hunting dogs Canis Major and Canis Minor, fighting Taurus the bull. He is sometimes depicted hunting Lepus the hare.
The Orion Nebula is also believed to be the 'Birth Place' of stars and it is quite possible that our very own sun was born here.
The image shown was taken by RJS Photography and was given by kind permission.
How many Constellations are there and How are they Named?
There are 88 constellations which are named after mythological beings. Although some constellations may resemble the animals or people they are named after, others were merely named in honor of those figures. The constellations are spread throughout the whole celestial sphere, the imaginary sphere in space that surrounds the Earth.
Constellations are visible on any clear night. The particular constellations you can see depends on your location, the time of year, and the time of night. As the Earth makes its daily rotation about its axis and its yearly revolution around the sun, the celestial sphere appears to shift. As a result, different constellations come into view.
Betelgeuse (see image above) is located in the constellation Orion and it is known as a red giant. It has been calculated that Betelgeuse is 370 times larger than our Sun and 1000 times brighter. As Betelgeuse is about 640 light years from us, we are seeing it as it was 640 years ago so it is possible that the star has gone supernova, we just haven't seen the event yet. Betelgeuse was the first star ever to have its size measured, and even today is one of only a handful of stars that appears through the Hubble Space Telescope as a disk rather than a point of light. In1921, Francis G. Pease and Albert Michelson used optical interferometry to estimate its diameter was equivalent to the orbit of Mars. Last year, new measurements of the distance to Betelgeuse raised it from 430 light years to 640, which increased the star's diameter from about 3.7 to about 5.5 AU.
The above information was sourced from Wikipedia
The lifecycle of a star
Stars are a fascinating component of our universe. They may seem like permanent objects in the sky, but technology has allowed us to photograph the heavens, and now we know more about stars than ever before. They are born, they live, and then they die. How does this happen?
A star’s life is long compared to that of a human, but we can see the stages of stellar birth, aging, and death in the heavens. They follow a pattern similar to many of the life cycles we see here on earth. Stars are born, they “grow up,” exist many years, and then they die, and there’s an exciting battle between the force of gravity and gas pressure too that makes it exciting and potentially explosive!
Stars are born in nebulae. Huge clouds of dust and gas collapse under gravitational forces, forming protostars. These young stars undergo further collapse, forming main sequence stars.
Stars expand as they grow old. As the core runs out of hydrogen and then helium, the core contacts and the outer layers expand, cool, and become less bright. This is a red giant or a red super giant (depending on the initial mass of the star). It will eventually collapse and explode. Its fate is determined by the original mass of the star; it will become either a black dwarf, neutron star, or black hole.