The Leo Triplet — M65, M66 & NGC 3628
Leo · Askar FRA400 · ToupTek ATR585M · Sky-Watcher AZ-EQ6 PRO · 2026-03-25
Acquisition
| Filter | Exposures | Sessions |
|---|---|---|
| Luminance | 95 × 120s | 6 |
| Red | 35 × 180s | 6 |
| Green | 27 × 180s | 5 |
| Blue | 21 × 180s | 4 |
Total integration: 7h 19m
Astrometric Data
Field Center
11h 19m 52.1s
+13° 18′ 54″
Pixel Scale
0.746 ″/px
Orientation
-92.15°
Field Radius
0.833°
Objects in Field
Main Challenges
Three galaxies at three different inclinations in a single frame create a processing problem: the edge-on NGC 3628 wants aggressive background suppression to reveal its dust lane and tidal tail, while M65 and M66 need subtlety to preserve colour gradients in their disks without oversaturating. The tidal tail of NGC 3628 extends faintly away from the group — it is present in the data but demands careful deconvolution and noise handling to pull out cleanly. A deeper luminance stack would help considerably.
From the Field
Six evenings across nine days, each running about 90 minutes before the target moved behind the balcony horizon. The Leo Triplet transits at 42–44 degrees from Torria — accessible but never high, and the usable window per night is tight. The sequence opened every session at around 19:35 as M65 cleared the obstruction, and ran until the target dipped back toward the limit. Two frames from the final night came from the dawn tail of a Pelican Nebula session — NINA pivoted to Leo for four minutes at 05:34 before the sky closed, adding a pair of R frames at 54 degrees altitude and the best guide RMS of the run.
Opening session. Guide RMS 0.24″ — clean night, all frames usable.
Worst session of the run. Guide RMS 0.57″ — 2.4× the run average. Most of the L and R rejections trace back here.
Recovery session. Guide RMS 0.31″ — improved, all frames kept.
Guide RMS 0.27″. Slightly higher start altitude due to earlier meridian crossing. Clean session.
Guide RMS 0.28″. Luminance-heavy session — 21 L frames in 81 minutes.
Guide RMS 0.27″. Shortest main session — 55 minutes. Luminance-only focus, 4 R frames added.
Dawn tail — 2 R frames at the end of a Pelican Nebula session. Best guide RMS of the run (0.14″), highest altitude (54°). Four minutes at the edge of the night.
Process Notes
Thirty-five million light-years away, three spiral galaxies are pulling on each other. M65, M66, and NGC 3628 form a genuine gravitational group — the Leo Triplet — close enough in space that their interactions have left visible marks on all three. M66's arms are asymmetric, distorted by the group's mutual gravity. NGC 3628 carries a tidal tail stretching away from the others, drawn out by the same forces over hundreds of millions of years. M65 has stayed more composed, its tightly wound arms less disturbed than its neighbours, but it is not immune.
All three fit in a single field from the FRA400. No mosaics, no compromises. The geometry of the group — two face-on spirals flanking one edge-on, each showing a different aspect of the same gravitational story — is what makes the Leo Triplet one of the great wide-field galaxy targets in the spring sky.
Three Galaxies, Three Perspectives
M65 (NGC 3623) is the most orderly of the three: an inclined Sa-type spiral with tightly wound arms, a prominent central bulge, and a relatively smooth disk. Little disturbed, structurally conservative. In LRGB it renders with a warm core and a faint, dusty lane along the near edge.
M66 (NGC 3627) shows the interaction most clearly: its arms are pulled out of symmetry, one side brighter and more extended than the other. A strong dust lane crosses the central region. M66 has hosted supernovae in both 1989 and 2016 — it is an active, evolving system.
NGC 3628 is the visual anchor of the group: an edge-on Sb/c spiral whose defining feature is the dark equatorial dust lane cutting the disk in two. The Hamburger Galaxy, informally. More importantly, it carries a tidal tail extending northeast from the disk — a river of stars drawn out by the group's gravity, faint but present in the data. Pulling it fully out of the noise requires depth; it is there in this integration, at the limit of visibility.
LRGB for Galaxy Colour
Galaxies demand colour fidelity more than almost any other astrophotography target. The stellar population gradients — old red stars concentrated in the bulge, younger blue stars tracing the spiral arms — are scientifically and visually meaningful, and they are subtle. A poor LRGB blend erases them. The split exposure strategy (120s luminance for structure and depth, 180s RGB for colour signal) separates the concerns: the luminance stack drives resolution and detail, the RGB channels provide the colour overlay.
Software
Stacked and processed in PixInsight. Acquisition managed with N.I.N.A., autofocus via ZWO EAF through the ToupTek AFW-M 8-position filter wheel.
Behind the Scenes
Six sessions, all running the same 90-minute window between 19:35 and 21:30. The Leo Triplet transits at 44 degrees from Torria — it never gets high, and the accessible arc before it drops behind the balcony horizon is tight every night. NINA opened the sequence the moment M65 cleared the obstruction and ran until it didn't.
Sessions
| Date | Frames | Filters | Window | Alt range | Guide RMS | Focus drift |
|---|---|---|---|---|---|---|
| 2026-03-17 | 40 | 21×L + 7×R + 6×G + 6×B | 19:45–21:28 | 27.0°–44.5° | 0.24″ | 8 steps |
| 2026-03-19 | 29 | 14×L + 6×R + 6×G + 3×B | 20:01–21:18 | 27.0°–42.3° | 0.57″ | 8 steps |
| 2026-03-20 | 32 | 14×L + 6×R + 6×G + 6×B | 19:36–21:14 | 27.4°–44.3° | 0.31″ | 8 steps |
| 2026-03-23 | 34 | 16×L + 6×R + 6×G + 6×B | 19:35–21:04 | 29.3°–44.4° | 0.27″ | 8 steps |
| 2026-03-24 | 32 | 21×L + 8×R + 3×G | 19:37–20:58 | 30.1°–44.2° | 0.28″ | 8 steps |
| 2026-03-25 | 25 | 21×L + 4×R | 19:58–20:53 | 34.8°–44.0° | 0.27″ | 8 steps |
| 2026-03-26 | 2 | 2×R | 05:34–05:36 | 53.8°–54.2° | 0.14″ | 0 steps |
What Got Rejected
194 NINA frames total. 178 made it into the final stack — 16 rejected (8.2%). The luminance channel absorbed most of it: 107 L frames captured, 95 used (11.2% rejection). Red lost 4 frames out of 39 (10.3%). Green and blue came through untouched — 27/27 and 21/21.
The March 19 session is the obvious culprit. Guide RMS of 0.57 arcseconds is 2.4 times the run average. The other six sessions held between 0.14 and 0.31 arcseconds — tight, consistent, professional. One bad night degraded 15% of the luminance data and a proportional share of the red. The calibration routine caught it.
The Dawn Tail
The last two frames in the stack came from 05:34 on March 26 — four minutes at the end of a Pelican Nebula session that ran all night from the opposite end of the sky. When the Pelican sequence completed, NINA switched targets and grabbed two R frames of the Leo Triplet before the sky closed. At that hour, the Triplet was at 54 degrees altitude — the highest of any session, near transit, 10 degrees above where it sits during the evening window. Guide RMS: 0.14 arcseconds, the cleanest of the entire run. Two frames from the remnants of another project's night.
Post-mortem
The 90-minute window per evening is the real constraint on this project. The target geometry from Torria gives a 44-degree peak altitude — workable, but not generous — and the accessible arc is cut short on both ends. The solution is what happened here: six consecutive evenings running the same sequence, accumulating in narrow bands of time. The March 19 guiding degradation cost 16 frames, none of which were critical. The overall rejection rate of 8.2% is clean. More luminance depth and a second dedicated blue session would deepen the tidal tail of NGC 3628 and improve colour balance. The data is there; the tail just needs more photons to come fully out of the noise.