Mars at close opposition (October-November 2005)
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(October-November 2005)
By Salvador J. Ribas
During the last stretch of October and the first of November, the indisputable main object of night skies was the planet
Mars.
Mars as seen by the
Hubble space telescope during the approximation of 2003.
(Courtesy of
NASA and the
STScI)
A
superior planet is said to be at opposition when it is directly on the opposite side of the
Earth from the
Sun. This implies it rises at the sunset, passes the
meridian at the middle of the night, and finally sets at the very moment the
Sun rises again from the east skyline. It also implies that the planet is brightest than at any other position of its
orbit, because we can see its whole disc directly lighted up by the
Sun.
Earth and
Mars configuration at the moment of the opposition.
(By Salvador J. Ribas)
Mars spends about 687 terrestrial days to completely revolve around the
Sun, following a slightly elliptical
orbit. That is why two special positions exist: the nearest to the
Sun (
perihelion), and the furthest (
aphelion). If we take into account the time the
Earth spends revolving the
Sun, it is easy to conclude that every 26 months (2.2 years) an opposition occurs.
Because of the
orbits of planets are elliptical, oppositions can be more or less appropiate for observation, depending on the exact position the planet occupies on its
orbit. In fact, oppositions are always the moment of gratest brightness, but if they occur when the planet is near its
perihelion, obviously a grater amount of light reflects on its disc and so we see it still brighter. In summer 2003 an
exceptional close opposition took place, the best for 58 thousand years. The distance between
Mars and the
Earth was only 56 million kilometers and as a result,
Mars's apparent size was 25.1
arcseconds.
The opposition we are talking about was quite favourable and occured on the early morning of 30th October. The distance from
Mars to us was 69 million kilometers and the apparent size was significantly over 20
arcseconds.
Agrupaciķ d'Astronomia d'Alella
5th November 2005, Alella (Barcelona)
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