NGC 2362 - Captured by Dr. James Dire

NGC 2362, also known as Caldwell 64, is a rare gem of an open cluster, easily identified by the dominant bright star at the center.  It was first discovered by Giovanni Batista Hodierna sometime before 1654.  The cluster sits behind the bright star Tau Canis Majoris so it is often called the Tau Canis Majoris Cluster.  It is a relatively young cluster, around four to five million years old and contains a mass of about five-hundred solars.  Associated with the massive nebula Sh2-310, they lie about the same distance.  However, the nebula is more of a photographic object.  There doesn’t seem to be any correlation to the cluster and Tau Canis Majoris except alignment from our perspective.

With an apparent magnitude of 3.8, the cluster is well within reach of even the smallest telescope.  Of course, the larger the aperture, the more stars will pop out and the more details will become available.

Dr. James Dire: LVAS Friend from Hawaii

NGC 2362 is an open star cluster in the constellation Canis Major.  The cluster is mag. 3.8 and is 5.0 arcminutes in diameter.  It can be found 2.75º northeast of the mag. 2 star, Wezen.  The cluster owes most of its brightness to the mag. 4.4 star, Tau Canis Majoris.  Tau is a five-star system with the two brightest stars, Tau A and Tau B, having mags. 4.9 and 5.3, respectively.  The pair is separated by 0.15 arc sec.  Tau A is a spectroscopic binary with a 155-day period.  One of those two is an eclipsing binary with a 1.28-day period.  Thus, Tau A is a triple star.  A mag. 10 star orbits the Tau A and B pair and is 8 arcseconds away.  All of the Tau A and B system are thought to be massive O-type stars.  The eclipsing binary stars are only 0.1 AU apart, the spectroscopic companion about 10 AU away, while Tau B is at 223 AU and completes one orbit per year around the Tau A trio.  The mag. 10 star is 13,000 AU away and close encounters with other cluster stars will eventually pull it out of orbit.

There are around 60 more stars in the cluster, many young O and B stars.  The cluster lays 4,800 light years away and is thought to be relatively young, around 5 million years.  This is the same age as the island of Kauai, where I live.

I viewed the cluster with two telescopes, a 70mm f/6 refractor and a 10-inch F/10 SCT, under dark Kauai skies.  Both views were very different.  When I looked directly at the cluster in the 70mm at 35X, all I could see was Tau, as it overwhelmed the remaining stars.  However, when using averted vision, the fainter stars in the cluster popped out forming a halo around Tau, which didn’t appear to be as bright.  Moving my eye back and forth, I could make the cluster and Tau blink on and off.  The effect was very similar to viewing a planetary nebula with a bright central star.

In the 10-inch at 97X, the entire cluster is resolved and visible around the eyepiece’s field of view.  The cluster appeared very similar to the picture I took, shown herein (see Jim's image of NGC 2362 above in the Introduction).

Photo details:  60 minute exposure, 102mm f/6.3 apochromatic refractor, SBIG ST-2000XCM CCD Camera -10°C, March 15, 2012, KEASA Observatory, Barking Sands, Kauai, Hawaii.

Jay And Liz Thompson: LVAS Members from Henderson, Nevada

(Click on images for larger view.)

We observed NGC 2362 on February 17th and 19th through 10-inch and 14-inch telescopes from our backyard in Henderson, NV.  This fine open cluster is centered about Tau Canis Majoris, which is a visual triple (see left image).  An image taken Feb 19, 2012 (see center image) approximates our visual impressions.  We also viewed a bonus object, the Winter Albireo (H 3945), which lies a degree or so north of the cluster (see right image).

Buddy Barbee: LVAS Friend from North Carolina

This observation of NGC 2362, known as the Tau-CMa cluster and Caldwell 64, was made Friday, Feb 17, 2012 from the backyard of my home in Winston-Salem, NC.  I was using a 5-inch Mak-Cass with a 24mm eyepiece for a magnification of 79X.  It was a beautiful clear night with a mild temperature of about 44º F.  The naked-eye limiting magnitude was only 4.3.

Using a 24mm eyepiece for a magnification of 79X and a true field-of-view of 52 arcminutes, finding NGC 2362 was very easy with the scope’s GOTO.  I did my alignment on Capella and Alphard, entered NGC 2362 into the controller, pressed enter and then GOTO and there it was, almost dead center in the field-of-view.  Normally, from a dark sky site, there is a faint gray haze behind the cluster, but looking at the cluster in town with all the light pollution; the sky was much too bright to see this haze.  Upping the magnification to 146X with a 13mm eyepiece, I could count 17 stars around Tau-CMa in a circle having a diameter of 8 arcminutes.  This cluster has a Trumpler Classification of I2r, which means that it is detached from the surrounding star field with a strong concentration toward the center, has a large range in brightness and is rich in stars (more than 100).  I would say that is an excellent description of the cluster except for the number of stars visible in it.  On the best of nights with my 10-inch Dob, I have never seen more than about forty stars in this cluster.  Still, this cluster is often described as a jewel surrounded by diamond dust and that is how it appears even in town with fewer stars visible.

NGC 2362, the Tau Canis Major cluster, is sometimes called the Mexican Jumping Bean Cluster, due to an interesting effect that occurs when the telescope is tapped.  The cluster’s fainter stars will appear to stop moving while the bright central star, Tau Cma, continues to move.  This happens due to a phenomenon known as persistence of vision and is a very neat effect to watch.  Give it a try and see what you think.

Jaakko Solaranta: LVAS Friend from Finland

NOTE: I observed the cluster on four separate dates and provided three drawings to accompany my notes.

Date:  Apr 18/19, 2004

Instrument:  Naked eye and 5x21mm finder

Location:  Base del Teide, Tenerife, Spain (7,480ft)

NE Lim. Mag.:  7.1

Weather:  -0°C, very cold, but excellent.

Description:  Easily visible with the naked eye as a fuzzy patch surrounding Eta CMa.  No sign of resolution but a simple 5x21 finder revealed a strong glow surrounding the named star and few faint members from it.

Date:  Mar 31, Apr 1, 2008

Telescope: 120mm refractor

Location:  Los Cancajos, La Palma, Spain

NE Lim. Mag.:  6.0

Weather:  +17°C, NE wind, clouds

Description:  Dominated by the mag. 4 Tau CMa.  Low power reveals an obvious glow surrounding the star in the center which is bright enough to interfere with night vision.  Quite symmetrical.  A lovely cluster.

Date: Nov 25/26, 2011

Telescope: 120mm refractor

Location:  Playa de Fañabé, Tenerife, Spain

NE Lim. Mag.: 5.2 (SQM-L: 18.80)

Weather:  +16.8°C, 1016 hPa, clear, humidity 65%

Description:  Gorgeous cluster dominated by the brilliant mag. 4 Tau Canis Majoris.  In total 40+ mag. 9-13 stars visible within a slightly E-W elongated area of 5’ x 7’.  Brighter stars are mostly packed south of Tau CMa.  Symmetrical and several chains of stars especially in the N and S sides.  Stars form a familiar shape of a ladybug hence the nickname “The Ladybug Cluster”.  Outside the field, to the east, a small river of stars flows north of mag. 6 star HD 57192.  Large and sparse open cluster ASCC 37 is located 30’ NW from Tau CMa and appears as a 10’ x 7’ grouping of mostly mag. 10 and 11 stars.

Date:  Mar 13/14, 2012

Telescope:  80mm refractor

Location:  Koivukylä, Vantaa, Finland

NE Lim. Mag.:  4.8 (SQM-L: 18.31)

Weather:  +0°C, humidity ~54%, 1017 hPa, sun -12° below the horizon.

Description:  Fairly easily visible even at an altitude of 5° and such small aperture.  The cluster does not rise higher than this from Southern Finland (60° 18’ north 25° 03 east) so the object is nothing more than a shadow compared to its real appearance.  The cluster is surrounding - but mostly south of - Tau Canis Majoris, which displays only a few mag. 10 members and a faint background glow.

Fred Rayworth: LVAS Secretary and AL Coordinator from Las Vegas, Nevada

I first observed this highly unusual and distinct cluster on Jan 25, 1996 from my back yard in Tipton, Oklahoma.  With a 16-inch home-made f/6.4 Dob at 70x, my notes say:  “Wow!  Very small open cluster consisting of odd shape with about twenty stars grouped around a central bluish one.”

My next observation was with the same scope, same magnification from Sunset Overview at Lake Meade, Nevada on Jan 23, 2004.  I described it almost the same with “Wow!  Bright star closely surrounded by about 20 even magnitude stars.”

The next observation, this time with a 16-inch f/4.5 and a magnification of 87x, was done from a bike trail parking lot on Blue Diamond Road, Nevada, and an extremely lousy observing site.  It was actually the highlight of the evening for such a light-polluted observing session.  “Nice surprise.  Quite beautiful small open cluster dominated by a bright central star.”

By far, my most detailed observation, and the one I did purposefully for this challenge was a month early, on February 25, 2012 from Spring Mountain Ranch, Nevada, just in case March wouldn’t pan out, which it didn’t, as it turned out!  Using a 16-inch f/4.5 with magnifications ranging from 40x to 102x to 131x, I logged the following notes:  “Wow!  (I say Wow! a lot.)  A gathering of maybe 30 medium-bright stars with a super bright one right in dead center.  Has sort of a rust orange tint to it.  Right behind it is a hint of haze suggesting more stars that aren't quite resolvable, but not sure if that's just the glow from that star or something more.  There are quite a few stars visible and I can count about 20 outright.”

Unfortunately, when I drew the picture, I forgot to add in the haze.  Also, I probably threw in more than 20 dots (I didn’t actually count), so my drawing is just a generalization of what I saw, not the actual image.  I’m no artist and make no bones about it.  Our other contributors are, so go to them if you want more accuracy.  The drawing I made that night in my log book is no better!

Roger Ivester: LVAS Member from Boiling Springs, North Carolina

Date:  Feb 25, 2012

Location:  Backyard in Boiling Springs, North Carolina

Conditions:  Both seeing and transparency excellent

NELM:  5.0

Telescope:  102-mm refractor without diagonal

Magnification:  Sketch @ 82x

Pencil Sketch:  5 x 8 white notecard with colors being inverted using my scanner.

A beautiful and most interesting open cluster, however, many faint stars were subdued by the brighter star, mag. 4.4 Tau Canes Majoris.  The greatest concentration of stars appeared to be on the western edge, but were very difficult, creating an unresolved haze, mostly in part, due to the intense glare of Tau.  There was very little resolution of the stars when using the 4-inch refractor at low magnification with only the brightest members visible.  When increasing the magnification to 82x, approximately 20 stars could be counted.  A much better resolution of the cluster would’ve been possible, if not for one annoying streetlight.  The cluster had a very irregular appearance, with all of the stars appearing mostly bluish-white.

Gus Johnson: LVAS Friend from Maryland.

Tau seems to be a cluster member. There are two listed companions, mag. 10 at 8.2" and mag. 11 at 14.5”.  On March 5, 1991, I found both almost too easy with my 6-inch Newtonian at 98x.

As to the cluster in my 4 1/4-inch reflector at 28x, it isn't quite adequate.  A formerly owned 5 1/4-inch at 39x gave a nice view.  When using my 4 1/4-inch at 38x, I noticed a nearly equal pair a quarter of the way between UW and Tau.  UW is almost as bright as Tau and is 1/2º to its’ north.