Download Sky Notes - February 2012 - North Devon Astronomical Society

North Devon Astronomical Society
Sky Notes - February 2012
THE MOON
New Moon 21st February
First Quarter N/A
Full Moon 7th February
Last Quarter 14th February
THE PLANETS
Mercury
Mercury will pass through superior conjunction, (on the far side of the Sun, as seen from Earth), on the
7th, but will become visible again in the evening sky by the end of the month.
Venus
An unmistakable object in the western evening sky, Venus sets around four hours after the Sun by the
end of February.
Mars
Currently tracing a retrograde loop* back into the constellation Leo, the Red Planet’s brightness shows
a steady increase from magnitude -0.6 to -1.2 as it approaches opposition next month.
Jupiter
Though still a fine sight in the evening sky among the stars of Aries, Jupiter is slowly beginning to sink
towards the western horizon, and sets at 11.00pm by the end of the month.
Saturn
Rising before midnight, Saturn can be found close to the bright star Spica, in the constellation Virgo.
Uranus
An early evening object in the constellation Pisces.
Neptune
Currently in conjunction with the Sun, Neptune is unobservable this month.
FEBRUARY HIGHLIGHTS
3rd
Comet 2009/P1 (Garradd) passes very close, (around one third of one degree) to the globular cluster
M92 in the constellation Hercules. This could present a fine photo opportunity for all you imagers...
7th
Between 1.09am and 1.19am on the morning of the 7th, Saturn’s largest moon Titan will occult the
eleventh magnitude star PPM 196978. This event should be visible in moderately sized telescopes,
although the apparent dimming and brightening of the star, as it appears to pass behind Titan, will be
better observed in larger instruments.
20th
A second occultation occurs in the early hours of the 20th, when the planet Saturn itself passes in front
of another eleventh magniude star, PPM 196966. The star will be seen to emerge from the planet’s
southern limb around 2.42am.
25th
A fine line-up of Solar System objects occurs on the evening of the 25th when, (in order of increasing
altitude), Mercury, Uranus, Venus, a slim crescent Moon and Jupiter appear spread out over a fortyfive degree arc of sky. This could present yet another good photo opportunity...
* The apparent ‘backwards’ motion of the planet against the sky, caused by the Earth catching up with,
and then passing Mars in its orbit.
CANIS MAJOR
CONSTELLATION CLOSE-UP
This month, we will take a close-up look at the
constellation Canis Major - The Greater Dog.
Canis Major is difficult to see in it’s entirety, due
to the constellation’s southerly declination,
which ensures that, for observers in the UK, it is
usually seen low down in the south among the
atmospheric haze. It is, however, easy to locate
thanks to it’s unmistakable leading star Sirius.
With an apparent magnitude of -1.46, it is the
brightest star visible in the night sky, (see below).
4
M50
6
CANIS MAJOR
.
Sirius
$
Murzim
M41
(
NGC 2362
VY
k
Another of the 48 patterns devised by Ptolemy
in the second century AD, Canis Major is said to
represent one of the hunting dogs belonging to
Orion, (not to be confused with the northern
hunting dogs of the constellation Canes Venatici).
ORI
MONOCEROS
Wezen
LEPUS
Canis Major covers an area of around 380 square
COLUMBA
,
degrees, sitting astride the band of the southern
0 Adhara
.
Milky Way, and contains some very interesting
objects. The first of these is VY Canis Majoris which is, in terms of radius, the largest star
known. It’s brightness is somewhat variable, but with an average magnitude of +7.8, it is visible in binoculars and
small telescopes. In addition, the constellation also contains the recently discovered Canis Major Dwarf Galaxy the closest satellite galaxy to Earth. However, it is obscured visually by the dust in the plane of our own galaxy, so
it’s probably not a good idea to spend too much time hunting for it!
Canis Major is relatively poor in targets for small to medium aperture telescopes, with one notable exception:
M41 Mentioned in a work by Aristotle from the year 325 BC, this open cluster could lay some claim to being the
longest-known deep-sky object of all. However, the first formal identification of what would later be called
M41 dates to 1654, and the object was catalogued by Messier in January 1765 as a cluster of stars which
appeared nebulous in his small telescope. Easily visible in binoculars and small telescopes, M41 lies some
four degrees south of Sirius, (Alpha Canis Majoris), and contains around 8,000 stars, (though only a fraction
of these are shown in amateur instruments). Current estimates give M41 a physical diameter of about 24
light-years and put the cluster’s distance at approximately 2260 light-years.
Sirius No study of Canis Major would be complete without a look at the constellation’s primary star - Sirius.
( CMa) Also known as ‘The Dog Star’, Sirius is the brightest star visible in the night sky, and is also one of the closest
at just 8.6 light-years distant. This proximity partly explains why Sirius appears so bright to us, but we must
also consider the physical properties of the star itself. Sirius is a hot, white star of Spectral class A and has a
surface temperature of around 10,000 degrees Celcius - about twice as hot as our Sun. In fact, it’s name is
derived from the Greek ‘Seirios’ meaning ‘glowing’ or ‘scorcher’ - very appropriate. In addition, the star is
somewhat larger than the Sun, more than twice as massive and around 25 times as luminous! Interestingly,
Sirius also has a white dwarf companion - Sirius B, also known as ‘The Pup’, which can be glimpsed in large
telescopes under the right conditions.
Canis Major is bordered by the constellations Monoceros, Lepus, Columba and Puppis.
Society meetings are held on the first Wednesday of each month at the Methodist Church Hall, Rhododendron Ave,
Sticklepath Hill, Barnstaple. Meetings begin at 7.45pm and all are welcome to attend, regardless of experience.
For more information please contact NDAS secretary Julie Buckingham at [email protected] or call
Mark Buckingham on 01271 345374.