Download Sky Notes - December 2011 - North Devon Astronomical Society

North Devon Astronomical Society
Sky Notes - December 2011
THE MOON
New Moon 25th December
First Quarter 2nd December
Full Moon 10th December
Last Quarter 18th December
THE PLANETS
Mercury
Visible in the morning sky from the middle of the month, Mercury reaches greatest western elongation
on the 23rd, when it rises two hours before the Sun.
Venus
Venus is currently visible very low in the evening sky, it’s apparent distance from the Sun increasing as
the month progresses.
Mars
Although still fairly small, the apparent size of the Red Planet increases by more than 50 percent
during December. It can be found in the early morning hours, among the stars of Leo.
Jupiter
A prominent object in the constellation Aries, Jupiter culminates, (reaches it’s highest point in the sky),
in the early evening, so is still well placed for observation. However, it will set at 2.00am by the end of
the month.
Saturn
Becoming a prominent morning object in the constellation Virgo, near to the bright blue star Spica,
Saturn is gaining in altitude daily, and by mid-month will be 25 degrees above the horizon by 6.00am two hours before sunrise.
Uranus
Uranus is currently visible in the early evening among the stars of Pisces.
Neptune
An early evening object in the constellation Aquarius, Neptune sets around 8.30pm by the end of the
month.
DECEMBER HIGHLIGHTS
Visible throughout the month, Comet Levy, (P/2006 T1), continues it’s slow eastward journey through
the constellation Pegasus, crossing the north-eastern, (top-left), corner of the ‘great square’ during
December. Brightening to magnitude +7.7 by month’s end, the comet should be a relatively easy
binocular object.
14th
Peak of the Geminid meteor shower. Active between the 6th and 19th December, the shower should
reach peak activity - around 60-70 meteors per hour, on the morning of the 14th. Unfortunately, a
bright, waning gibbous Moon will doubtless reduce the number of meteors actually seen.
22nd
Peak of the Ursid meteor shower. With it’s radiant in the constellation Ursa Major, (but close to the star
Kochab in Ursa Minor), the second shower of the month will be active between the 17th and the 25th,
with the peak occurring on the night of the 22nd / 23rd. Low rates of 10-15 meteors per hour are
expected, but the Moon should not interfere this time.
ORION
CONSTELLATION CLOSE-UP
This month’s constellation close-up looks
at probably the most popular of the northern
hemisphere’s winter patterns - Orion.
Representing the mighty hunter of Greek
mythology, Orion covers 594 square degrees
and sits astride the celestial equator. It is a
prominent group which contains some of the
brightest stars in the entire sky.
TAURUS
(
GEMINI
Aldebaran
ORION
>
8
Betelgeuse
(
Bellatrix
NGC 2238
Chief among these are Betelgeuse and Rigel,
(Alpha and Beta Orionis, respectively).
M78
,
k
Betelgeuse is an M-class, red supergiant star
which is thought to be nearing the end of it’s
life. It is a semi-regular variable whose
apparent magnitude fluctuates between +0.2
and +1.2. Current estimates place Betelgeuse
at a distance of around 600 light-years and it
is the eighth brightest star in the sky.
.
0
M43
M42
$
$
4
MONOCEROS
6
Rigel
ERIDANUS
LEPUS
CANIS MAJOR
Rigel, on the other hand, is a blue supergiant
with 17 times the mass of the Sun and about
.
:
Sirius
85,000 times the luminosity! Rigel exhibits
$
some very slight variability but, despite an
estimated distance of around 775 light-years, it’s size and power ensure that the star appears the sixth brightest in
the sky. In fact, despite being designated ‘Beta’, at magnitude +0.18, Rigel is actually the brightest star in the
constellation. Orion contains three objects from the Messier catalogue, including probably the most well-known
nebula of them all:
M42 The Orion Nebula. A large emission nebula which covers more than one and a half degrees of sky, M42 is
easily visible to the naked eye as a fuzzy, fourth magnitude star. Visually, it is a fine sight in any telescope,
appearing slightly ‘greenish’ in large instruments. In long-exposure photographs, however, the nebula is
even more impressive, displaying highly detailed knots and swirls of coloured gas and dust. M42 is a stellar
nursery and much of the nebulosity we see in our telescopes is slowly condensing to form new stars. In
fact, it is energy from some of these newly formed suns, (principally, the stars known as ‘the trapezium also visible in a small telescope), which is ‘exciting’ the gaseous material, causing the nebula to shine.
M43 Although catalogued as a separate object, M43 is, in fact, just a detached portion of M42 and is visible as a
‘comma’ shaped patch in the same field of view.
M78 Often overlooked due to it’s proximity to M42/43. this object is the only principal reflection nebula in the
Messier catalogue. Unlike emission nebulae, (such as M42), reflection nebulae shine simply by reflecting
the light of nearby stars towards us. M78 can just be seen as a faint spot in 10x50 binoculars, but a small
telescope will reveal a small patch of nebulosity surrounding two 11th magnitude stars.
Orion is home to the annual Orionid meteor shower, which is associated with comet Halley and shows peak
activity in late October each year.
Orion is bordered by the constellations Gemini, Taurus, Eridanus, Lepus and Monoceros.
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.