Framing the Heart and Soul Nebulae (IC 1805 and IC 1848)

The Heart and Soul are a wide pair of H II regions in Cassiopeia, both listed in Sharpless’s 1959 catalogue: IC 1805 as Sh 2-190 and IC 1848 as Sh 2-199. They are big, they are close together, and they sit high in the northern sky in autumn, which makes them a favourite for short refractors and full-frame sensors.

How big they are depends on whom you ask

Object	Sharpless	NGC 2000.0	Lynds
IC 1805, Heart	150′	60′	60′ × 60′
IC 1848, Soul	120′	60′	40′ × 10′

The factor of two to three between catalogues reflects different boundaries: Sharpless traced the whole ionized region, while the other values describe brighter parts. In SIMBAD both identifiers resolve to the open clusters inside the nebulae, so SIMBAD’s own dimensions (13.3′ and 24′) are cluster sizes, not nebula sizes. This page uses the Sharpless values.

Both in one frame

From SIMBAD positions the two centres are 149.3′ apart, the Soul lying east-south-east of the Heart. Drawn as circles of their Sharpless sizes, they fit in a box of about 284′ × 150′ when the long side follows the line between them:

Sensor	Pair spans 80 % of the frame	90 %
APS-C IMX571	227 mm	256 mm
Full frame IMX455	349 mm	392 mm
1-inch IMX533 (square)	110 mm	123 mm

That puts the pair in camera-lens and small-Petzval territory. The 250 mm setup in the table below frames the Heart alone at about 70 % of the frame height; holding both needs the camera rotated by roughly 30° from landscape and leaves little margin. A full-frame sensor at 250–390 mm is the most comfortable single-frame option for this pair.

Mosaics

Covering the pair plus 10 % margin with 15 % overlap takes three panels at 400 mm with an APS-C sensor and six (3 × 2) at 550 mm. The mosaic planner shows the layout for other focal lengths, and its sensor-rotation check matters here because the pair’s long axis is tilted on the sky.

One nebula at a time

Alone, the Heart’s 150′ circle fills 90 % of an APS-C frame’s short side at about 325 mm; the Soul’s 120′ at about 405 mm. If you plan with the smaller NGC 2000.0 sizes instead, those limits double or more, but the frame will crop the outer nebulosity that the Sharpless boundary includes.

Season and altitude

The Heart culminates at local midnight in late October and the Soul in early November. At about +61° declination both are circumpolar from mid-northern latitudes (about 79–80° maximum altitude from 50° N) and never rise from 35° S.