The M.A.S.
Newsletter
Journal of the
Mauritius Astronomical Society
November 2000
The Next Meeting:
The next meeting, weather
permitting, will be due Friday 24th of November at 19:30 at Collège du Saint
Esprit, Quatre Bornes for the observation of the planets Saturn and Jupiter close to
opposition.
The sky this month:
Opposition for Saturn occurs on the
19th, and for Jupiter on the 28th. Telescope owners can find the
great red spot crossing the central meridian of Jupiter (at best on the Earth facing side
of the planet) at the date and time shown below.
13th 01:15,
21:06 22nd 03:37,
23:29
15th 02:53, 22:44
25th 01:07, 20:58
18th 00:22, 20:13
27th 02:44, 22:36
20th 02:00, 21:51
30th 00:14, 20:05
02nd 01:52, 21:43
The Leonids:
The meteor shower is back this year
with its maximum on the night of the 17th to 18th. The show will
start at about 02:00 and the peak of activity is expected after sunrise. The moon, at last
quarter, will somewhat spoil the show. Internet sites:
www.estec.esa.nl/spdwww/leonids
www.leonid.arc.nasa.gov/index.html
www.imo.net
News:
An international team of astronomers announced
Wednesday it has discovered four more moons orbiting Saturn, apparently putting the gas
giant back on top as the planet with the greatest number of known satellites. The four
faint bodies, spotted over the last two months at telescopes scattered across the globe,
bring the number of known moons orbiting Saturn to 22. With that, Saturn edges out Uranus,
with 21 natural satellites, on the moon front. Estimates of their size -anywhere from 10
to 50 kilometers across - are based on assumptions of their reflectivity. However,
astronomers have been able to determine that the irregular moons - meaning they orbit
outside the plane of Saturn's equator -are not asteroids, thanks to orbital calculations
done by Brian Marsden of the Harvard-Smithsonian Center for Astrophysics. Nor are they
likely to be comets. "The probability of that is very small," said Gladman, of
the Observatoire de la Côte d'Azur in France. Gladman added that several more months of
calculations should allow astronomers to pin down the moons' orbits. The four moons are
the only other irregular Saturnian moons found since William Pickering spotted Phoebe in
1898. The moons are believed to orbit Saturn at a distance of anywhere from 10 million to
20 million kilometers. In contrast, Saturn's moon Titan - which will be visited by
Cassini's Huygens probe in 2004 - orbits just 1.2 million kilometers from the planet.
Unlike Saturn's regular moons, which formed from the accretion disk that once surrounded
the planet, the newly discovered satellites were likely captured into orbit after the gas
giant formed. As such, the "new" moons are actually quite ancient. Indeed, the
icy bodies could very well be primitive remnants of the earliest building blocks of the
solar system. For now, the additional moons bear the provisional code names of S/2000 S1,
S2, S3 and S4. Following additional observations, the International Astronomical Union
(IAU) will certify them as true planetary satellites, and more lyrical names will be
given. By astronomical convention, Saturn's moons bear the names of Titans and other
figures taken from ancient Greek mythology. Between 1997 and 1999, the same team
discovered five more moons orbiting Uranus. While the astronomers caution the new
discoveries at Saturn are preliminary, they also said they have discovered other objects
that are likely Saturnian moon candidates. Promising a further bounty, the spacecraft
Cassini should reveal even more satellites within Saturn's rings after it arrives in orbit
around the planet in 2004.
Some Astronomical Terms:
Opposition: The position of an outer
planet when it is opposite the Sun in the sky. Then the planet is at its closest approach
to the Earth and reaches its highest point in the sky (culminates) at midnight. As
the orbits of the planets are elliptical, some oppositions bring the planets closer to
Earth than others.
Culmination: The moment when a
celestial object reaches its maximum (and also minimum for circumpolar objects) altitude
above the horizon as the Earth's rotation takes it across the sky. Circumpolar stars
culminate above and below the pole, these events are called upper and lower culmination
respectively.
Some Internet Sites:
www.astrosurf.com
www.jpl.nasa.gov
www.club-internet.fr/perso/legault
www.maison-astronomie.com
www.eso.org
www.pds.jpl.nasa.gov/planets
www.ghgcorp.com/akelly
www.astronomynow.com
www.medas.fr
www.fourmilab.ch
www.spaceviews.com
www.heavens-above.com
Serge Florens, Secretary
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