Archive for November 23, 2019

IC 1805 – “Cluster + Nebula” In Cassiopeia – December 2019 – Observer’s Challenge Report #131

November 23, 2019




Report #131

IC 1805 Open Cluster in Cassiopeia

Observer’s Challenge Report Final:  Click on the following link



Note:  The following are mostly original notes, with very little if any editing, to preserve the feelings and thoughts of the observer during the observation.  This is not the “official” Observer’s Challenge report, but what I call a “work-file” just to organize the entries.  Roger Ivester

     IC 1805 is a 6.5-magnitude cluster about 62 stars that spans about 20 arcminutes. It’s nearly centered on the group’s brightest member, HIP 11832 shining at magnitude 7.1. The cluster is young at only 2.5-million years and we see it at a distance of roughly 6,500 light-years. IC 1805 is enveloped in and associated with the emission nebula Sharpless 2-190, commonly called the Heart Nebula, which sprawls across 1.6 º of sky.

     Edward Emerson Barnard discovered IC 1805 photographically and included it on the first two plates of his wonderful Photographic Atlas of Selected Regions of the Milky Way.  The atlas can be viewed online at:     Intro by Sue French  


IC 1805, December 2019, Observing Report by Mario Motta: 

Color Image:  This was combined with 1 hour each of Oxygen 2 filter and Sulfur filter:  See attached.

IC 1805 (the Heart Nebula), North is to the right on this image, rotated to show the “heart” shape more readily.

Of course…to a cardiologist the Right heart (on the left, person facing you), is very “enlarged” so this is a rather sick heart, with what I would call right heart failure.    Mario Motta 





Sue French: Observer from New York:

14×70 binoculars:

IC 1805 is a fairly large, loose open cluster of six to eight moderately bright stars, depending on the borders, plus about 15 more stars on the backdrop.

105/610mm (4.1-inch f/5.8) refractor

     17×: Nebulosity is faintly visible without a filter, a little better with a UHC filter, and very nice with an O III filter. The brightest areas include: the IC 1805 cluster; a wide arc that runs between clusters IC 1805 and NGC 1027 and then loops around north of the IC 1805 cluster; and a small patch in the position of the nebula complex NGC 896/IC 1795. A fainter arc starts between the two clusters, loops around south of cluster IC 1805 and then northward on the western side of this cluster.  Both loops are quite patchy with very uneven brightness. Nebulosity also stretches from cluster IC 1805 to the eastern loop.

     87×: About 40 stars are visible in cluster IC 1805. Its brightest member is a double star, residing in a rough circlet of fainter suns at the cluster’s heart. Arms of stars starting north and south of the circlet curve westward. Two fairly bright stars northeast form a faint star with the lucida.  A broad scattering of stars straggle east through southeast from the circlet, while extremely faint specks of light can be seen within the circlet and rounding out the group.

     The double star is Stein 368 AB (STI 368 AB), PA 97º, separation 9.9″, component magnitudes 8.0 and 10.1. NGC 1027 displays about 50 stars centered on the group’s central lucida. Starting north-northwest of the star, its brightest attendants spiral outward from it for about 1½ turns.

     These observations were made in the northern Adirondack Mountains of New York, where my naked-eye limiting magnitude near Polaris was 6.3.


Roger Ivester:  Observer From North Carolina 

     In November I used a 6-inch f/6 reflector in an attempt to see the nebula in IC 1805. My eyepiece of choice for this night was a 2-inch-barrel 26mm with an O III filter. This gave me a field of view of 2º. 

     Scanning the area before using the O III filter, I first saw open cluster NGC 1027. A bright cluster at magnitude 6.7, consisting of about 20 stars with one brighter member located in the center. This cluster is located just to the east of IC 1805. 

     Now to IC 1805: I could easily see the cluster of stars located in the central region of the IC 1805 nebula. When adding an O III filter, I scanned the area for more than an hour; however, I cannot say definitively that I could see any nebulosity.

     On December 15, 2019, I used an 80mm f/5 refractor, with a 24mm eyepiece and a UHC filter. I was a bit dubious before beginning my observation that I’d be able to see the IC 1805 nebula based on my results using a 6-inch reflector only a month earlier, and with similar sky conditions. 

     After about thirty minutes, I could not see any of the nebula, but the central stars were easy and bright. However, when I began using my “manual” slow-motion controls, I began scanning across the IC 1805 area, and to my surprise, I began seeing very faint brightenings in the area. I scanned one section at a time, and was able to sketch extremely faint tentacles and fingers of nebulosity, only marginally brighter than the background. After more than two hours of “slow-motion” scans, well over two hundred crossings, I was able to sketch some of the brighter sections, encircling the central cluster. 

Telescope: 80mm f/5 achromatic refractor 

Eyepiece: 24mm + UHC filter 

Sketch Magnification: 17× 

Field of View: ~3.5º 

Roger IC 1805


James Dire:  Observer From Illinois 

     The Heart Nebula, IC 1805, is part of a vast complex of nebulae located in the constellation Cassiopeia. The nebula is located five degrees southeast of the star Segin and eight degrees east of the star Ruchbah. Segin and Ruchbah are the two easternmost stars making up Cassiopeia’s “W” asterism. 

     The brightest part of the Heart Nebula is separately known as NGC 896. NGC 896 was discovered by William Herschel in 1787 using his 18.7-inch reflector. NGC 896 measures 27 x 13 arcminutes and is estimated to be magnitude 10.

     The Heart Nebula itself extends about one degree in both right ascension and declination. The Heart Nebula lies 7500 light years away in the Perseus arm of the Milky Way Galaxy.

     IC 1805 is also the designation of an open star cluster in the middle of the Heart Nebula. This cluster is also known as Melotte 15. This loose open cluster is estimated to be a mere 1.5 million years old and contains several bright stars 50 times the Sun’s mass. These stars are responsible for exciting the hydrogen gas in the Heart Nebula resulting in the red glow as seen in photographs.

     My image of IC 1805 was taken with a 71 mm f/4.9 apochromatic refractor using an SBIG STF-8300C CCD Camera. The exposure was 140 minutes. In the image north is up and east to the left.

     The second image has labels pointing out the location of NGC 896 and the central star cluster in IC 1805. Two more open clusters are labeled in the image. The first is NGC 1027 located on the east side of the heart. NGC 1027 is a bright rich cluster of approximately 50 stars all within a 20 arcminute circle. The cluster has a total magnitude of 6.7. The other cluster is called Markarian 6 and is located southwest of the heart. Markarian 6 is magnitude 7.1 and is 6 arcminutes in diameter. All three star clusters contained in the nebula are worthy of inspection with any telescope at medium to high powers.

     My best view of the Heart Nebula was with my 14-inch f/6 Dob using a 26mm eyepiece (82x). This combination provides a one-degree true field of view. While the view comes nowhere close to my image, it was possible to see many of the brighter regions of the nebula, especially NGC 896 and the three above-mentioned star clusters.