Challenge #4 – C71, Open Cluster in Puppis
| Target | Type | R. A. | Dec. | Constellation | Magnitude | Size |
| C71 (NGC 2477) | Open Cluster | 07h 52m 10s | -38° 31′ 00″ | Puppis | +5.8 | 15.0 arcmin |
Overview
Discovered in South Africa in 1751 by Abbé Lacaille, this cluster contains about 300 stars of tenth magnitude and fainter, is around 700 million years old, and is a beautiful sight to behold. We’re unsure of its exact distance from Earth, but it’s believed to be about 3-5,000 light-years.
Unfortunately for us in the northern hemisphere mid-latitudes, it doesn’t rise much more than 10° above the southern horizon and so we never get to enjoy the clearest views of it. It’s the most likely reason too for such a magnificent view not being captured by Messier in his catalog.
In the sky, it covers an area almost the size of the moon. As you can see from the image below, it lacks the tight core of a globular cluster but is, nevertheless, a beautiful object to see.
Finder Charts
This first finder chart shows the sky at 21:30 in the middle of March and contains stars to magnitude five. The moon and planets are not shown.
The easiest way to find Puppis low in the south is to begin with the brightest night sky star: Sirius. You can see it to the lower left of Orion’s left ‘foot’.
Once you’ve found the unremarkable shape of Puppis, identify Naos, the magnitude 2.2 Zeta star of the constellation.
This last chart has stars to magnitude seven and you can see a naked-eye ‘hop’ from Naos to C71 via HR 3140 and b Puppis. You can also find it by drawing a line from a Puppis through b Puppis.
Remember, this cluster is visible to the naked eye under a dark sky but because it’s low on the horizon you may still need magnification to bring it to view.
In the last section, you’ll discover what you can see of this stunning cluster.
Individual Telescope Views
The following views will help you find C71 in different telescope types by presenting the images as your telescope will show them. The first image is with a black sky and white stars, the second picture is the same image but presented in inverse monochrome. Stars are shown to magnitude 10.0 and Naos, a Pup and b Pup are all labelled.
Each image can be clicked on for a full-screen version.
Upright View – This is what your eyes see unaided and through a reflex or red-dot finderscope
Upside-down view – This is what reflectors and magnifying finders show, and refractors / Cassegrains without a star diagonal
Mirrored View – Refractors and Cassegrain models with a star diagonal show this view
Observation
Even at low magnification you can’t help but be blown away by the beauty of this cluster. The stars in it are tight enough to make it feel like we’ve prized open a globular cluster with our telescope. Very many of the suns in this group are well resolved at even moderate magnification in a smaller telescope.
More magnification brings fainter stars to the light show and it’s easy for one’s brain to see loops, lines and other patterns at play between the individual members.
PDFs for Printing
Each of the star maps above is reproduced as a pdf below. Each star map has a number in [square brackets] beneath it which corresponds to the file number below. If you want image [C71-1], for example, click the ‘download’ button next to it below and you’ll be able to open it as a printable pdf.