Brief concepts of astronomy

Horizontal coordinates or Altazimuth

The Altazimuth coordinates use two basic levels: the altitude and azimuth. The azimuth (abbreviated AZ), measured from the North cardinal point east. This is how often appears in astronomical software and other sources, but in reality, if the observer is located in the southern hemisphere, is measured backward from the South to the West. Few references take this into account, therefore all tend to use the first method: from North (0°) to the east.

The altitude (Al) is measured from the horizon (0°) to the zenith (90°), so this coordinate is the angle between the object observed with the horizon. A negative level mentioned when the object is below the horizon, the point 90° below the horizon (Al .: -90) is called nadir.

NOTE: To our astronomical research in Second Life we ​​will use this kind of coordinates, but with reference to the azimuth the usual measurements of a compass, with the same position used for aircraft and ships (0° to 360° of the compass and Directional taken clockwise, from west to east).

Equatorial Coordinates

 The north-south line connecting both poles and passes through the object determines its decline. The decline (d) is measured from the celestial Ecuador to the poles, positive north and negative south. The celestial Ecuador has zero declination, and the poles declines +90 (north) and -90 (south).

 Right Ascension (RA) is measured on the celestial Ecuador from the gamma point (or vernal equinox) to the east, from 0 to 24 hours (1 hour equals 15 degrees) The gamma point is the point where the ecliptic crosses the celestial Ecuador from south to north.

 NOTE: This is the system that is commonly used in astronomy to find objects in a sky chart, being able to see this in the charts attached PDF file.

Elements of study in astronomy

Astronomy comprises the scientific study of everything that is not on Earth. This it sounds very vague, but it gives an idea of ​​the breadth of the discipline. Even some include the study of the Earth as a planet, compared to other similar bodies. Therefore, astronomy is stars, planets, comets, asteroids, nebulae, star clusters, galaxies, etc.

For example, what we see things astronomical day? Thus, the sun, the moon, the morning star, the evening star Venus, which usually will be correct answers. In a way, the shadows are also astronomical phenomena, as the sunlight causes. Similarly, the blue color of the sky has to do with the sun. We could even include the rainbow, and other atmospheric phenomena formed by light of the sun…

And at night? We have the moon, planets, stars, some know maybe comets, nebulae, clusters and galaxies. Satellites are also seen. Shooting stars, although they occur in our atmosphere, about 200 Km. Of height, also they have to do with astronomy, because it is of extraterrestrial material that falls on the Earth (like the meteors and meteorites). But at first glance we can reduce our field to various types of objects: the sun, moon, planets, and stars.

NOTE: For our purposes in SL we will use only the information on the sun and stars.

Constellations

The
 stars that can be seen on a clear night are certain figures that we call "constellations", and they serve to more easily locate the position of the stars. In total, there are 88 groups of stars that appear on the celestial sphere and taking its name from religious or mythological figures, animals or objects. This term also refers to limited areas of the celestial sphere comprising groups of stars with your name.

NOTE: SL constellations we see in the night sky will be those that we create, and some related to those normally see and we have to identify ourselves.

Stars

The stars are masses of gas, mostly hydrogen and helium, which emit light. They are at very high temperatures. Inside there are nuclear reactions. The Sun is a star. We see stars except the Sun, as very small bright spots, and only at night, because they are at enormous distances from us. They seem to be fixed, maintaining the same relative position in the sky each year. In fact, the stars are moving fast, but at such great distances that their position changes are perceived only through the centuries.

NOTE: In SL we can make several studies of the stars, especially their size and movement.

Planets

This derives from a Greek word meaning wanderer, and is a body that does not emit its own light, but shining in the sky reflected light, which is in orbit around a star. From a physical standpoint, a planet may be formed of solid materials, such as rock and metal, or by a cluster gas. From a genetic point of view, it is now thought that planets are formed by condensation processes of gas and dust around one or more stars. Our solar system would therefore not a unique case, but one of the many existing in the Universe.

Moon

The Moon is the only natural satellite of the Earth. Its diameter is about 3,476 km, about a quarter of the Earth. The mass of the Earth is 81 times that of the Moon. The average density of the Moon is only three-fifths of the density of the Earth, and surface gravity is one-sixth that of Earth. The Moon orbits the Earth at an average distance of 384,403 km and at an average speed of 3,700 km / h. Completes its revolution around the Earth in an elliptical orbit in 27 days, 7 hours, 43 minutes and 11.5 seconds. As it takes to revolve on its axis the same time to circle around the Earth, always showing the same face. The rotation of the Earth and the orbital motion of the moon are combined in such a way that the output of the Moon is delayed of about 50 minutes each day. New
 moon or new moon is when the moon is between Earth and the Sun and therefore we do not see (this is the best time for all to do their research astronomer, not affect the moonlight). In the first quarter, the Moon, Earth and Sun form a right angle, so that you can see in the sky half moon, in its period of growth. Full Moon or Full Moon occurs when the Earth is between the Sun and the Moon; it receives the rays of the sun on your face visible, therefore, is complete. Finally, in the three bodies Quarter Moon re-form a right angle, so that you can see in the sky the other half of the lunar face.

NOTE: In SL we will not take into account the moon, because it does not have any change for the time it takes to travel the vault of heaven.

Nebulae

Nebulae are regions of the interstellar medium consisting of gas (mostly hydrogen and helium) addition of chemical elements in the form of cosmic dust. They have a significant cosmological importance because many of them are the places where stars are born by condensation phenomena and aggregation of matter; at other times it is the remnants of stars already extinct or extinct (taken from wikipedia).

Galaxies

A galaxy is a collection of stars, gas clouds, planets, cosmic dust, dark matter and energy together gravitationally. The amount of stars that form a galaxy is uncountable, from dwarf galaxies with 107, to the giant galaxies, with 1014 stars. As part of a galaxy substructures exist as nebulae, star clusters and multiple star systems (taken from wikipedia).

Star clusters

A star cluster is a group of stars drawn together by their mutual gravity. The traditional classification includes two types of star clusters: globular clusters and open clusters (taken from wikipedia).

You can obtain more information in this page: **Astronomy For Beginners**

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