TSS Monthly DSO Challenge for April 2025

[kt4hx]

It’s that time again! We have a new month and some new targets for you to pursue, whether you be a visual observer, sketcher or imager. The sky has shifted a little more of course bringing some new stuff to center stage, but don’t forget the March objects either if you have not visited them yet. They too are still accessible. So let’s take a closer look at what I have selected for you this month.


Northern Celestial Hemisphere:

Messier 65 / NGC 3623 (Leo, barred spiral galaxy, mag=9.3, size=9.8’x2.9’, SBr=12.8):
Messier 66 / NGC 3627 (Leo, barred spiral galaxy, mag=8.9, size=9.1’x4.2’, SBr=12.7):
NGC 3628 (Leo, barred spiral galaxy, mag=9.5, size=14.8’x3.0’, SBr=13.4):
Representing the northern celestial hemisphere this month I have selected the Leo Triplet. This trio of galaxies is a spring staple just below the lion’s hindquarters. The two main components, Messier 65 and 66 were discovered by Charles Messier on 01 March 1780, with the third, NGC 3628, discovered by William Herschel on 08 April 1784.

The galaxies form an isosceles triangle tipped slightly NNE, with NGC 3628 at the apex about 36’ north of M66 and about the same distance NNE of M65. The two Messier galaxies lie closer together at the base of the triangular grouping, separated by about 20’. At a distance from us of about 35 MLY, the trio is an actual interacting group. Collectively the group is found in Dr. Halton Arp’s Atlas of Peculiar Galaxies under the category “Groups of galaxies” as Arp 317. M66 displays signs of distortion due to interaction in the past, most likely with NGC 3628, and itself is found in the Arp atlas as Arp 16 in the category titled “Galaxies with detached segments.”

The appearance of the two parallel ovals of M65 and M66 close together with the dimmer elongated thin oval of NGC 3628 oriented perpendicular to the Messier galaxies laying to their north is an intriguing view in the same field. Look for brighter cores within the Messier duo, as well as the possibly of an uneven mottled appearance within M66. The larger elongated disk of NGC 3628 may also appear uneven along its major axis due to the dark lane bisecting its edge on disk.

So take your time to both locate and study this fine trio of galaxies, to see what you can pick out within their respective envelopes. They lie in a rich area of the sky for galaxies and are certainly highlights of the early spring sky. Take a gander at the Triplet in the below Sloan Digital Sky Survey (SDSS) image to relish in their true beauty.

Southern Celestial Hemisphere:

NGC 3372 (Carina, emission nebula, mag=3.0, size=2.0°):
Let us travel to the large southern constellation, Carina the keel, which was formerly part of the gigantic constellation Argo Navis. Here we will pursue what I believe is the finest emission nebula in the sky. That is not said to negate the prominence and beauty of Messier 42 in the least. But the first time I laid eyes on this behemoth I was simply astounded. Discovered telescopically by Nicolas-Louis de Lacaille in 1751, it was also observed numerous times by James Dunlop. John Herschel had this to say about the nebula: "It is not easy for language to convey a full impression of the beauty and sublimity of the spectacle which this nebula offers, as it enters the field of the telescope fixed in R. A., by the diurnal motion, ushered in as it is by so glorious and innumerable a procession of stars, to which it forms a sort of climax, and in a part of the heavens otherwise full of interest."

Known famously as the Eta Carinae Nebula, even from about a Bortle 5 suburban location just south of the equator I found it an easy naked eye object and very bright and curious in 10x50 binoculars. With a scope of most any aperture it turns into a true showpiece of various clumps and knots of nebulosity, permeated by dark lanes in various directions. It truly is a visual wonder.

Embedded within its huge glowing field are various open clusters such as Trumpler 14, 15 and 16 as well as Bochum 10. Of course there is also the namesake star Eta Carinae, which is expected to go supernova at some point soon, in astronomical terms that is. There are two lobes emanating from this star, known as the Homunculus Nebula. These lobes are the result of an outburst from Eta Carinae in the late 1840s into the 1850s which saw the star brighten from about magnitude 1.5 to -1.0. This even was chronicled by John Herschel. Eta Carinae now shines at about magnitude 6.4 biding its time. Also within the nebula complex is a prominent dark nebula within the complex, named the “Keyhole Nebula.”

This object is a true gem of the southern sky and is a fine target for visual (and sketchers) observers and imagers alike. So why not turn your scope its way to enjoy its bright silent beauty, with its undertone of violent activity from Eta Carinae. The below image (public domain from Wikipedia) reveals the beautifully immersive character of this object.

NGC 3115 (Sextans, lenticular galaxy, mag=8.9, size=7.2’x2.5’, SBr=11.9):
We next head to the heavenly sextant. This constellation straddles the celestial equator, but our target lies almost 8° to its south. Sometimes called the spindle galaxy it is bright even from my typically Bortle 5 backyard. It appears as a thin sliver of bright diffuse light, with a core that is brighter still. Its central bulge tapers out to thin tips at both ends.

Discovered by William Herschel in 1787 he described it as bright, large and extended. This lenticular is the brightest galaxy in Sextans, a constellation frequently overlooked by observers since it is not bright and contains no Messier objects. With its brightest star (Alpha) shining meekly at magnitude 4.5 the constellation lies quietly between Leo and Hydra.

NGC 3132 (Vela, planetary nebula, mag=9.2, size=1.5’x1.4’, SBr=9.7):
We finish up this month in another former portion of the old constellation Argo Navis. Vela the sails is home to this excellent planetary nebula informally known as the Eight Burst Nebula or the Southern Ring Nebula. Discovered on 02 Mar 1835 by John Herschel, he recorded it as a "planetary nebula, very large, very bright, elliptic.”

I recommend using at least a narrow-band nebula filter to give it more visual contrast. Even better is an O-III line filter for bringing out detail with the nebula’s disk. I found while observing it with a 5-inch refractor that without a filter the magnitude 10.0 central star tended to overwhelm the envelope of the planetary, so using a filter will tame that star allowing one to see more of the nebular structure. It is a fine object for imagers who wish to experiment with trying to pull out deeper details. So give it a try and see what you can do with this nice planetary.


There you have it for this month. I hope you enjoy the pursuit and the challenges that I have presented to you, whether you live north, south or closer to the equator. The sky is a treasure trove of wonderfully beautiful objects of many types, and they are just waiting for those with the desire and patience to find them. Please post your results here for all to share. Good luck friends!

[helicon]

Thanks for sharing the April objects Alan. Saw them all through the 10" Dob. Will see if it can be witnessed in a 4" scope, 3628 will probably be tough. Overall I hope a lot of folks will try out the Triplet, getting two galaxies at a minimum in the same field of view is almost as exciting as Bode's nebula and the Cigar galaxy (M81 and M82)

[kt4hx]

Thanks for sharing the April objects Alan. Saw them all through the 10" Dob. Will see if it can be witnessed in a 4" scope, 3368 will probably be tough. Overall I hope a lot of folks will try out the Triplet, getting two galaxies at a minimum in the same field of view is almost as exciting as Bode's nebula and the Cigar galaxy (M81 and M82)

Thank you Michael. Depending upon one's sky quality of course, all three of the triplet should be achievable with a 4 inch. I find NGC 3628 is not significantly more difficult than M65, but of course its larger angular size reduces its surface brightness, which can certainly be impacted by brighter skies.

I have always found the presence of more than one galaxy within the same field of view to be engaging. Whether it be two, three or sometimes more. Good luck with your observations.

[kt4hx]

I have observed the Leo Triplet (M65, M66 and NGC 3628) multiple times over the years. The smallest aperture I utilized was an ST120 refractor I used to have years ago. The two primary galaxies were small, but obvious at 38x. The third one not difficult, appeared dimmer due to its lower surface brightness. This was at a location that was judged to be a Bortle 4 at the time.

The following observations happened in April of 2021 at our dark site location utilizing the 17.5 inch dob. Conditions were a solid Bortle 3.

Messier 65 / NGC 3623 (Leo, barred spiral galaxy, mag=9.3, size=9.8’x2.9’, SBr=12.8):
Aiming the scope at mag 3.3 Theta Leonis (Chartan), I slipped south while viewing through the 8x50 RACI. I quickly found 73 Leonis (mag 5.3) just over 2° to the SSE. In the same view I could easily see mag 7.1 HD 98388 to its east. This star lies along the western side of the triangle formed by the Leo Triplet. South of the star I could just make out the presence of M65 in the finder as a tiny and very dim diffuse knot.

Moving to the eyepiece (94x) the triplet was seen easily all in the same 1.1° TFOV. M65 was a large and bright thin ellipse oriented north-south and displaying an inner lens of brightness anointed with a stellar core. Its disk seemed uneven in illumination as the eye moved across its face. Moving to 152x the sense of a curdled visual affect seemed more noticeable and the northern side of the disk seemed slightly brighter than the southern portion. Taking a look at 199x, I picked up a subtly brighter section with its outer arm near the northern tip of the visible envelope. This galaxy was quite fetching in the 17.5 inch, and I wasn’t done yet!

Messier 66 / NGC 3627 (Leo, barred spiral galaxy, mag=8.9, size=9.1’x4.2’, SBr=12.7):
Sharing the same FOV with M65 and just to its east, I now concentrated on M66. It was slightly more apparent in the RACI view. Taking my first look at 94x, it presented a bright and large oval that was thicker in breadth than was M65. Similarly it was oriented north-south but initially seemed more evenly illuminated than did M65. Like the previous galaxy, it also sported a bright inner lens with a stellar core set within it. A 9th mag field star lay in close attendance to its northwestern edge. Checking it out with 152x it now appeared more uneven in illumination across its envelope. The southern portion of the disk seemed more extended than the northern, and it also seemed to be subtly hooked toward the southeast, inferring its spiral structure. There also seemed to be a tiny knot of brightness just north of the core, likely an HII region. Going ahead to 199x, the sense of the southern arm hooking away from the core to the southeast was more noticeable, while the apparent HII region just off the northern side of the core was also more apparent, though still quite tiny. Again, this is a beautiful galaxy, with both similarities and differences in comparison to M65.

NGC 3628 (Leo, barred spiral galaxy, mag=9.5, size=14.8’x3.0’, SBr=13.4):
North of the previous two objects and perpendicular to their major axis, I easily spotted this delightful ghostly object at 94x. It was large and bright, but in a dim sort of way. To clarify, it was quite obvious in the FOV, but it was more subdued than its neighbors to the south having lower surface brightness. Its disk was a thin edge-on orientation that seemed quite mottled to the eye. Going ahead to 152x it was quite a curious sight indeed, with glimpses of its central dark lane seeming to cross its disk at an odd angle to the major axis. This gave it a very uneven light distribution along the major axis. The northern half of the galaxy was much more prominent while the southern half was very weak, with only a modest amount of its envelope visible below the dark lane. This impression was significantly reinforced when moving up to 199x and even 283x. The odd angle of the bisecting dark lane split the light from the galaxy disk into very unequal halves with the northern portion along the major axis clearly dominant to what was seen below the dark lane. It was a most curious visual appearance, and added immensely to the allure of this triplet visually

[Mike Q]

I checked out the Leo Triplet with the 16 a couple weeks back. Had all three galaxies in one eyepiece. It was a sweat view