27 Apr 2010 @ 13:32, by Unknown
april 27 2010
tuesday
earth
spring/fall
ho there well near as I can discern the center of the galaxy seems to lie south when it is summer in the northern hemisphere if that makes sense
[link]
by Martin J. Powell
Sagittarius is home to a wealth of interesting astronomical objects. This is mainly due to the fact that, when we look at Sagittarius, we are looking towards the centre of our own Milky Way Galaxy, where the density of stars and gas/dust clouds (nebulae) is greatest. Indeed, the actual centre of the galaxy is located at the South-eastern corner of the constellation, hidden behind dark clouds of interstellar dust, close to the boundary with Scorpius.
The Annual Visibility of Sagittarius
Sagittarius is best observed during the Northern hemisphere summer months (winter in the Southern hemisphere) because during this time the constellation is visible throughout the night and is seen in darkness when it is highest in the sky. Southern hemisphere observers have the best view of Sagittarius, since it crosses almost directly overhead in the sky. In general, the Northern hemisphere has a less favorable view - the visibility of the constellation being worse the further North one is situated. Indeed, the Southern section of the constellation cannot be seen at all from high Northern latitudes
Finding Sagittarius in the Night Sky
The position of Sagittarius in the sky depends upon the observer's latitude, the season of the year and the time of the day. The following method allows an observer to find Sagittarius in his or her sky at any time of the year, as well as knowing the sky conditions he/she is likely to encounter at the chosen time - whether night-time, twilight or even daylight. However, a few basic concepts first need to be explained.
Astronomers tracking the motion of a celestial body across the sky use a direction (bearing) along the observer's horizon (known as the azimuth) and an angle above the horizon (known as altitude or elevation). The azimuth is expressed in degrees measured clockwise from 0º (True North) through 90º (due East), 180º (due South) and 270º (due West). Azimuth is typically used for high-accuracy tracking of objects across the sky, e.g. for tracking individual planets or stars, and its value changes rapidly over time. Constellations, on the other hand, cover a relatively wide area of the sky and so there is little need for such high-accuracy measurements; we simply want to know roughly in which direction it will be found. Therefore, for these purposes, direction will be expressed not as an angle but in traditional points of the compass (North, North-east, South, etc.) which are more easily understood across the world, and which also simplifies the calculations required.
Sagittarius, like all celestial bodies, reaches its highest point in the sky when it crosses the observer's meridian; this is known as the meridian transit or culmination. This is, essentially, the 'best' time to observe it because it is then largely clear of the haze, turbulence and - in town and city locations - light pollution, all of which adversely affect the visibility of a celestial body when it is near the horizon.
The direction an observer faces to observe a zodiac constellation's meridian transit depends upon how high the constellation is positioned above his or her horizon when it transits; in the Northern hemisphere this will typically be due South; in the Southern hemisphere it will typically be due North. The situation is rather more complicated for observers in Equatorial latitudes, however, where most of the zodiac constellations transit at high altitudes (either just to the North or South of the zenith).
see site for more info
Site link = [link]
Copyright © Martin J. Powell July 2008 with minor additions March 2009
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