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A star hop through Monoceros (showpieces and asterims)

Introduction

In the beginning of January, around midnight, Monoceros (the Unicorn) culminates in the southern sky. Beginning observers of the deep sky often overlook this constellation, because it has no bright stars. In fact, from light polluted areas, it is practically impossible to find any naked-eye stars in this seemingly barren region between Betelgeuse (Orion), Sirius (Canis Major) and Procyon (Canis Minor).

Although the constellation of Monoceros is cut through by the winter Milky Way, it contains no stars brighter than the fourth magnitude. However, it holds a variety of nebulae, open clusters, multiple stars and asterisms that can be observed with small or medium aperture telescopes. In this star hop I will take you along some of the showpieces of Monoceros, a constellation almost invisible to the naked eye, but probably one of your favorite winter constellations, once you get familiar with the hidden treasures it holds.

In the first part of this article we visit the northern region of Monoceros, in the latter part the southern region. At the end of the article you will find a table with basic data on all the objects, a bibliography and two “Star hop charts” generated with Sky Tools 2 from CapellaSoft. The circles projected onto these star charts represent a field of view of 4 degrees. We start of with an overview map of Monoceros and the deep sky objects, which we will visit during this star hop. The overview map was generated with TheSky for Macintosh 5.0.7 by Software Bisque.


Monoceros overview map

Credit and © Software Bisque, “TheSky for Macintosh”



NGC 2264, The Christmas tree cluster (Collinder 112)


We begin our star hop in the northeastern corner of Monoceros with NGC 2264, The Christmas Tree Cluster. To find NGC 2264, take Alhena (24 Gamma Geminorum), a magnitude 1.9 star in Gemini as a starting point. From there go about 4° to the south-southeast, to the 3rd magnitude star Xi Geminorum. From there go about 3° south-southwest. There you will find NGC 2264, an open cluster of the 4th magnitude. In 10 x 50 binoculars, the cluster's triangular shape (Christmas Tree) should be visible. It spans about 30’ (half a degree) and contains about 40 stars. In my binoculars and Klevtzov-Cassegrain telescope (with diagonal mirror) the Christmas Tree appears to be standing upside down. In an inverting telescope (Newtonian) it appears right side up. The shape of the tree is very easy to recognize. At the base of the tree you will find the cluster’s brightest member, 15 S Monocerotis, a bright blue-white star of magnitude 4.6. At the top you will find a 6th magnitude star. Several stars of magnitude 8 to 9 mark the outline of the Christmas Tree Cluster.

NGC 2264 is embedded in a large nebulous area, holding molecular clouds in which star formation takes place. At the “top” of the tree, south of the 6th magnitude star, lies the Cone Nebula, which is very hard to detect visually. In medium and large aperture telescopes the Cone Nebula might be “visible” as a star-poor region. William Herschel discovered NGC 2264 in 1784 and the Cone Nebula in 1785.


NGC 2264

North is up, west is to the left. Faintest stars are of magnitude 12
Credit and © Software Bisque, “TheSky for Macintosh”


NGC 2261, Hubble’s Variable Nebula (Caldwell 46)


Once you have located NGC 2264, the Christmas Tree Cluster, it is very easy to find your way to our next deep sky treasure in Monoceros, NGC 2261 or Hubble’s Variable Nebula. Centre your finder scope on the 6th magnitude star at the top of the “Christmas Tree”. Just 1° to the south-southwest you will find Hubble’s Variable Nebula, a comet-shaped triangular patch of light.

William Herschel discovered this emission/reflection nebula in 1783. In 1916 Edwin Hubble was comparing photographs that had been taken between 1910 and 1916. According to Burnham Hubble found out that not only the shape and brightness of NGC 2261 varied, but also the details in the nebula showed changes from month to month and sometimes even from night to night. Ever since Hubble’s discovery, NGC 2261 has been called Hubble’s Variable Nebula. A star, R Monocerotis, illuminates the nebula. The variations in shape, brightness of and details of NGC 2261 are probably caused by shadows cast through a cloud of matter surrounding R Monocerotis.

The nebulas dimensions are 3.5′by 1.5′. At 133x through my 8-inch telescope it looks like a comet shaped, diffuse patch of light. A bright spot of light, R Monocerotis, forms the southern tip of triangular nebula. The nebula curves away a little into the northwestern direction. I have observed Hubble’s Variable nebula only once, so I cannot comment on the variations. However, when I observed it, it was very bright and very easy to find.

NGC 2261
William Sparks (STScI), Sylvia Baggett (STScI) et al.,
& the Hubble Heritage Team (AURA/ STScI/ NASA)


NGC 2244, an open cluster in the Rosette nebula


From Hubble’s Variable Nebula move south-southwest for about 4.5°. There you will find NGC 2244, a star cluster that can be identified easily because of its rectangular shape. The cluster is about 23′ in diameter and has a visual magnitude of 4.8. It’s brightest star shines at a magnitude of 5.84 (visual). In my 8 inch telescope the cluster looked very bright and I counted about 30 stars.

The cluster lies at the heart of the Rosette Nebula, a big emission nebula, about 80′x 60′, where star formation takes place. The nebula which is very large and very faint, has several “brighter” segments which all have there own NGC catalogue numbers. I’ve tried to detect the Rosette Nebula from my light polluted backyard using my 7 x 50 binoculars, but until now I did not succeed. Maybe a rich-field telescope or big binoculars under a dark sky will do the trick. I will keep you updated.


NGC 2244

NGC 2244, the open cluster at the heart of the Rosette Nebula



NGC 2301


From NGC 2244 we will hop on to our next stop, NGC 2301, an often-neglected star cluster near the centre of the constellation of Monoceros. There are several ways to get to this cluster. I will take NGC 2244 as a starting point. From NGC 2244 move to the southeast for about 5°, where you will find 18 Monocerotis, a 4.5 magnitude star. From 18 Monocerotis move south-southeast about 2°. There you will find NGC 2301.

From my suburban backyard using an 8-inch telescope NGC 2301 is a beautiful open cluster. In my 8x50 finder-scope it is visible as a faint smudge of light. NGC 2301 is a small cluster, with a diameter of 12′. I could only detect about 30 stars of a total of 80. The cluster is of the 6th magnitude and the brightest star is of the 8th magnitude (visual). There is a string of stars in the North-South direction. In the center you will find a beautiful pair, one is yellow and the other is blue-white. It reminded me of Albireo in Cygnus. The sketch below should give you an idea what to expect at the eyepiece.


Sketch NGC 2301

Sketch of NGC 2301 by M. Heijen
8 inch f10 telescope, 166 x, FOV 18'. North is up, West is to the left


11 Beta Monocerotis


We now move to the southwestern corner of Monoceros, to one of the most beautiful multiple stars in the sky, 11 Beta Monocerotis. To find this gem of the winter night sky, we start of at Saiph, or 53 Kappa Orionis, a star of Magnitude 2.1 that marks the left knee of Orion, the hunter. From there go east-northeast for about 10.5°. There you will find 11 Beta Monocerotis.

Beta Monocerotis is a triple star, with three components that look almost appear equal in brightness, and form a small triangle of bright white blue stars. A magnificent view at 150x! The A component is of visual magnitude 4.7. The B component, which lies at a position angle of 132°, is of magnitude 5.2. They are separated by 7.3". The C component has a visual magnitude of 6.1 and lies at a position angle of 124° from the A component and they are separated by 10". For the keen eyed observer there is a D component with a visual magnitude of 12.2. It lies at a position angle of 56° and is separated from the A component by 25.9".


Harrington’s Star 17 (The Unicorn’s horn)


From 11 Beta Monoceros go east-southeast 3°. There you will find one of the asterisms Phil Harrington describes in his book “The Deep-Sky, an Introduction”. It is a V-shaped asterism of six stars of the 9th and 10th magnitude. It’s about 8′x 8′ in size. Phil named the arrowhead-shaped asterism “The Unicorns Horn”. This seems appropriate, as it lies within the borders of Monoceros. From Harrington’s Star 17 we hop to another asterism in Monoceros, Harrington’s Star 18 or Pakan’s 3.

Harrington's star 17

North is up, west is to the left. Faintest star is of 12th Magnitude
Credit and © Software Bisque, “TheSky for Macintosh”


Harrington’s Star 18 (Pakan's 3)


From Star 17, move east-southeast about 3°. There you will bump into a string of 15 stars about magnitude 9 or 10 which together form a mirrored "3". The brightness is average. The size is about 25′to 30′. The asterism should be very easy to see in almost any telescope, and stands out well from its surroundings. It was first spotted by Randy Pakan of Edmonton, Canada. Because of this, the asterism is nicknamed “Pakan’s 3. Below you will find a sketch, made at the 8-inch f10 Klevtzov-Cassegrain, using a 32mm eyepiece, giving a magnification of 62.5x. The field of view is 46.5′. North is up, west is to the left.

Harrington's Star 18 - Pakan's 3

Sketch of Pakan's 3 by M. Heijen
8 inch f10 telescope, 62.5 x, FOV 46.5'. North is up, West is to the left



M 50 (NGC 2323)


From Pakan’s 3 we go to our final object in this star hop, M 50, the only Messier object in Monoceros. To find M 50, centre your finder scope on Pakan’s 3. Then go east-northeast for 2.5°. There you will find M 50, a fine open cluster. M 50 contains about 80 stars and has a diameter of 16′. In my telescope I could detect about 50 to 60 stars ranging from the 8th to 12th magnitude. The visual magnitude of M 50 is 5.9 and its brightest star is of magnitude 7.85. It is well worth a visit!

With M50, my star hop through Monoceros ends. I hope you have enjoyed it. Print it and have a go at the telescope in the oncoming winter months.


Object

Type

RA

DEC

Mv

Size

SA

MIL

U1

U2

Beta Mon

MS

06h28m49.1s

-07°01'59"

3.8

11

I-275

II-272

136

Rosette Nebula

EN

06h30m54.0s

+05°03'00"

5.5

80′x60′

12

I-227

I+II-227

116

NGC 2244

OC

06h32m21.4s

+04°51'45"

5.2

23′

12

I-227

I+II-227

116

NGC 2261

RN

06h39m12.0s

+08°45'00"

3.5′x1.5′

12

I-227

I-182

95

STAR 17 (Unicorn's Horn)

AST

06h40m41.0s

-08°59'59"

0.0

8′x8′

12

I-274

II-273

135

NGC 2264

OC

06h41m03.2s

+09°53'07"

4.1

20′

12

I-202

I-183

95

NGC 2301

OC

06h51m46.3s

+00°28'21"

6.3

12′

12

I-250

I+II-228

115

STAR 18 (Pakan's 3)

AST

06h53m04.0s

-10°07'41"

0.0

25′

12

I-298

II-273

135

M 50

OC

07h03m12.3s

-08°19'28"

5.9

16′

12

I-273

II-273

135


Legend:


MS

Multiple star

OC

Open cluster

EN

Emission nebula

RN

Refelection nebula

AST

Asterism

RA

Right Ascension

DEC

Declination

Size

Size of the objects in arc minutes

Mv

Visual Magnitude

SB

Surface Brightness

SA

Map number of SkyAtlas 2000

MIL

Map number of the Millenium Star Atlas

U1

Map number of the Uranometria 1st edition

U2

Map number of the Uranometria 2nd edition




Overview Starhop Monoceros

Star hop charts generated with SkyTools 2 by Capella Soft.

The image to the left shows the star hop along the first 4 objects of this article, NGC 2264 (The Christmas Tree Cluster), NGC 2261 (Hubble's Variable Nebula), NGC 2244 and NGC 2301. The image at the bottom shows the star hop along the last 4 objects, Beta 11 Monocerotis, Harrington's STAR 17, Harrington's STAR 18 and M50.

The circles in both star hops represent a field of view of 4 degrees (the Telrad finder or a standard finder scope used on a commercial telescope).


Overview starhop Monoceros


Bibliography



  • The Nightsky Observers Guide (Volume 1) by Kepple and Sanner
  • Deepsky Companions: The Messier Objects by Stephen James O' Meara
  • Deepsky Companions: The Caldwell Objects by Stephen James O' Meara
  • The Deep Sky by Philip S. Harrington
  • Burnham's Celestial Handbook (Volume Two) by Robert Burnham Jr.
  • Atlas der Sternbilder (German) by Slawik and Reichert
  • SkyAtlas 2000 second edition by Tirion and Sinnott
  • Millennium Star Atlas (Volume 1) by Sinnott and Perryman
  • A view of the Universe by David Malin
  • The Sky for Macintosh 5.0.7 by Software Bisque
  • Sky Tools 2 by CapellaSoft



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