Re: What astromony can do
- From: Sam Wormley <swormley1@xxxxxxxxx>
- Date: Wed, 28 Jan 2009 22:30:13 GMT
oriel36 wrote:
I quite enjoyed reading about the magnification hobby and the
chestbeating financial contest between participants here but
personally I prefer Marty's or Barbara's homely observations of the
night sky and rely on images from Hubble,Keck or other large
telescopes to do my own research.
Beyond magnification,which is a valuable facet of astronomy,there is
work to be done such as a closer link between astronomy (specifically
the motions of the Earth)...
Speaking of motions of the earth...
"The Earth rotates about its polar axis once a day and produces an
rotate clockwise.
"Superimposed on the diurnal rotation is an annual rotation caused by
the Earth's orbiting the Sun. Since the stars are seen by the naked eye
after sunset, the constellations appear to move from east to west, and
to return to the same position after a year. Relative to the Sun, the
stars rise and set roughly four minutes earlier each day. In the course
of a month, the night sky appears to move two hours in right ascension
to the west. Also because of this orbital motion of the Earth, the
circumpolar stars in the Northern Hemisphere appear to rotate once a
year in a counterclockwise direction around the north celestial pole
and in a clockwise direction about the south celestial pole.
"The Moon moves in an orbit inclined to the ecliptic by 5.1 degrees;
the Moon makes one revolution about the sky from west to east in about
a month. During this period the phases on the Moon complete a cycle
from new to full and back to new. The orbit of the Moon is moving
around the ecliptic, so that other aspects of the Moon's position in
the sky, such as its maximum and minimum declination, change from one
month the next. It is important to know when the planets are in the
most favorable position for observation. The outer planets, for
example, are best seen around opposition. They are in their least
favorable position around conjunction.
"The inner planets are different--they are in their most favorable
position near greatest elongation, even though they are not at full
phase. At superior conjunction the phase is around full, but the
planets are difficult to see because they are further from Earth and
usually too close to the Sun. At inferior conjunction the inner planets
are nearest to the Earth, but again they are difficult to see because
their phase is small, and they are too close to the Sun.
"Often the times of phenomena need not have any great precision;
sometimes the nearest hour, day, or even the nearest week are
sufficient for observational purposes. The dates and times, however,
usually depend on the coordinate system. For historical reasons the
conjunctions and oppositions of planets have always been calculated in
geocentric ecliptic coordinates. On the other hand, the conjunctions of
planets with other planets, bright stars, or the Moon have always been
calculated using equatorial coordinates; the phenomena are then
observed more easily with an equatorially mounted telescope. In some
cases the times of phenomena have been defined as the maxima or minima
of the distances from the Sun or the Earth or the elongation from
another body. In such cases, the phenomena are independent of the
coordinate system".
---From the Explanatory Supplement To The Astronomical Almanac (1992)
.
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