Continuing the tour of stellar objects crossing the meridian line this month: a double-star in Canis Major, a unique object called "The Intergalactic Tramp" takes the place of our galaxy; we present the Eskimo nebula and the Heart-shaped cluster.

Star: h 3945 (145 Cma) in Canis Major the ‘winter Alberio’

Location of h3945/145 Cma
08-Feb-2018 at 22:00h
(Click for full-size image)

Telescope, Easy

Ask any amateur astronomer what his favourite colour double star is and 7 out of 10 will probably say Alberio in Cygnus.  Others might cite delta Andromedae (Almach).  There is however one double star that might challenge them all – h 3945 (145Cma) in Canis Major.  It is arguably the most colourful double star in the winter sky and has been nick-named the “Winter Albireo.” 

h3945 (aka 145 Canis Majoris) was catalogued by John Herschel (William’s son) in the early 1800s.  The magnitude 5.0 primary is accompanied by a 5.9 magnitude companion 26.8 arc-seconds away.  Their spectral types (K0 and F0) give rise to a stunning colour contrast, bright citrus orange and royal blue.  It is therefore a pity that h3945 doesn’t get the plaudits it deserves from backyard astronomers, given that it is such a stunning site. 

Perhaps h3945’s southerly location as seen from the UK, coupled with its brightness (or lack of it) is the reason.  It is not as bright or easily seen as Albireo or Almach, but if your observing site affords a clear view of the lower half of Canis Major, then it should definitely be on your observing list.  To locate 145 Cma, just trace a line from1 CMa past 2 CMa and extend it about 3 degrees beyond (see finder chart) 145 Cma crosses the meridian on the 8th just after 22:00h.

Star: h 3945 (145Cma) in Canis Major (Image Credit: Mario Motta of Massachusetts)


Globular Culster: NGC 2419 "The Intergalactic Tramp" or "Wanderer"

Location of NGC 2419
14-Feb-2018 at 22:00h
(Click for full-sized image)

Telescope, Medium/Challenge

This unique object was discovered by William Herschel on December 31, 1788.  It lies at distance of almost 300,000 lightyears from the centre of our galaxy, making it one of the most distant known globular clusters, nearly twice the distance of the Large Magellanic Cloud. 

American astronomer Harlow Shapley nicknamed it "The Intergalactic Tramp" believing it to have possibly broken away from the Milky Way, however, recent observations indicate Shapley hypothesis was incorrect and NGC 2419 is still gravitationally bound to the Milky Way, just moving in a highly eccentric orbit.  At such a distance it's estimated it will take about 3 billion years to complete a single orbit around the centre of the galaxy.  Although rather faint, NGC 2419 is probably one of the largest and intrinsically brightest known globulars, estimated to contain well over a million stars across a spatial diameter of 400 light-years, comparable in brightness to the spectacular Omega Centauri.

NGC 2419 is positioned 7 degrees north and slightly east of Castor (α Gem - mag.  +1.58), About 4 arc minutes west of NGC 2419 is a mag.  +7.2 star with a double star of mag.  +7.9 a few more arc minutes further west.  NGC 2419 shines at magnitude +10.3 and has an apparent diameter of 5 arc minutes.  It's a somewhat challenging target especially under light polluted skies.  In good sky conditions it can be spotted with a small 100mm (4-inch) aperture, but a 150 mm (6-inch) scope is required to clearly reveal it as a small fuzzy object that's clearly non-stellar.  Scopes in excess of 18” are needed to resolve its brightest stars.  It crosses the meridian on the 14th at 22:00h. 

Globular Cluster: NGC 2419 "The Intergalactic Tramp" or "Wanderer"
(Image Credit: Bob Franke) (Click for larger image)


Nebula: The Eskimo Nebula (NGC 2392) or Clown face nebula

Location of NGC 2392:
12-Feb-2018 at 22:00h
(Click for full-sized image)

Small Telescope, Medium

A reflection nebula in the constellation Orion.  Again we shall steer clear of the obvious –M42 Orion nebula, and instead take a look at M78.  This was discovered by Pierre Méchain in 1780 and was included by Charles Messier in his catalogue.  M78 is the brightest diffuse reflection in the sky and lies in a group of nebulae that include NGC 2064, NGC 2067 and NGC 2071.  This group belongs to the Orion Molecular Cloud Complex located 1,600 light years distant from Earth.

M78 is easily found in small telescopes as a hazy patch which also involves two stars of 10th magnitude.  These two stars, HD 38563A and HD 38563B, are responsible for making the cloud of dust in M78 visible by reflecting their light The nebula is pretty easy to find as it is located only about 2 degrees north and 1.5 degrees east of Alnitak, the easternmost star of Orion’s Belt.  Due south Jan 16th – 22:00h.


Nebula: The Eskimo or Clown Face (NGC 2392) or Clown face. This false-color image is a
digital composite made from images taken at the Vatican Advanced Technology Telescope (VATT)
telescope on Mt Graham.  (Image Credit: Vatican Observatory) (Click for larger image)


Open Cluster: M50 the ‘heart shaped cluster’

Location of M50:
20-Feb-2018 at 21:00h
(Click for full-sized image)

Binoculars/Telescope, Easy

Messier 50 (M50), (NGC 2323) nicknamed the Heart-Shaped Cluster, is a large, appealing and relatively bright open cluster located in the constellation Monoceros.  Messier 50 was possibly discovered by the Italian astronomer and mathematician Giovanni Domenico Cassini before Charles Messier independently discovered and catalogued the cluster in April 1772

M50 has an apparent magnitude of 5.9, just about visible to the naked eye, appearing as a faint patch of nebulosity from dark sky locations.  It lies to the east of Orion, near the border between Monoceros and Canis Major. 

Through binoculars, M50 appears as a bright and relatively large patch of nebulosity with a few stars resolvable.  Small telescopes reveal the cluster’s distinctive heart-shaped figure containing a sprinkling of 7th and 8th magnitude stars, set against a background haze.  Viewed at low to medium powers in 6-inch to 8-inch telescopes, at least 40 blue-white stars including several yellow giants and a red M-class giant, positioned 7 arc minutes south of the cluster’s centre are visible.

Messier 50 has an angular diameter around 18 arc minutes, corresponding to a spatial diameter of 20 light years.  The dense core of the cluster spans 10 light years.  M50 has an estimated age of 78 million years; making it a very young cluster.  It lies at an approximate distance of 3,200 light years from Earth. 

Finding M50 is relatively easy.  Start by aiming your sights on Sirius, the brightest star in the night-time sky.  Located 9.5 degrees north-northeast of Sirius is M50, with θ CMa (mag.  +4.1) sandwiched halfway between them. 

M50 crosses the meridian on Feb 19th at 21:00h. 

Cluster: M50 the ‘heart shaped cluster’. (Image Credit: NOAO/AURA/NSF)