My first Magazine Sky & Telescope - 04.2019

APRIL 2019 OBSERVING Going Deep γ β μ NGC 4565 ε ζ NGC 2903 Algieba M64 η M85 α M53 Regulus N N p Left: This sketch of galactic cirrus in the Sickle of Leo is a mosaic of several drawings resulting from several “sweeps” of the telescope across the area. Right: This mosaic of the Coma Berenices region features not only galactic cirrus but also the tight globular cluster M53 and several galaxies. as 2–3% contrast, given good object composition in the ﬁ eld of view. I ﬁ nd that 100° apparent ﬁ eld-of- view eyepieces operated at maximum eye pupil of 5–7 mm are the best for detect- ing galactic cirrus. Consequently, I use very fast mirrors, f/2.6 to f/3.0, so as to achieve the desired pupil size. The result- ing ﬁ elds of view are eye-opening: 4.2° for the 6-inch f/2.8, 2.4° for the 10.5- inch f/2.7, 1.8° for the 13.2-inch f/3.0, and 1.1° for the 25-inch f/2.6. Not only is the face-on spiral galaxy M101 a won- derful view at low power in the 25-inch, with the spiral arms embedded in the glow of the galaxy, but there’s an arc of the Milky Way’s galactic cirrus at the edge of the ﬁ eld almost touching NGC 5474. At the same time, the smaller galaxies NGC 5485, NGC 5473, and NGC 5422 are visible. All this makes for an interesting effect, in which the view through the eyepiece appears ﬂ at yet my brain is telling me that the cirrus and galaxies form an immensely deep 3D view. I found myself staring at the ﬁ eld for a long time, unable to move to my next object. This leaves a visual memory and emotional astonishment that I can recall by looking at my drawing. I’ve begun stitching together ﬁ elds of view to form sketching mosaics. I’ll 58 A PR I L 2 019 • SK Y & TELESCOPE move the scope back and forth across several ﬁ elds of view, then pencil in what I see. From the end point, I’ll begin another sweep. I’ll then sweep all the way back to the very ﬁ rst ﬁ eld of view and repeat the sweeps one after the other until I build up a view up to 100 square degrees. I’ll usually go back a second or third night to conﬁ rm the sketch as well as tie up loose ends that I failed to knot the ﬁ rst time. The image of galactic cirrus in the Sickle of Leo with the pretty galaxy NGC 2903 above is a mosaic of several drawings, each drawing stretching over multiple ﬁ elds of view. Luckily it’s hard to get lost in Leo’s sickle with its prominent guide stars. Another mosaic of the Coma Berenices region not only features the galaxies NGC 4565, M85, and M64, but also the tight globular cluster M53. Comparing with views through other amateur telescopes, I’ve found that extraordinarily wide apparent ﬁ elds of view, dark skies, knowing what to expect at the eyepiece, and enhanced coatings all make a difference. Expe- rience also helps signiﬁ cantly: I see galactic cirrus much more easily now after three years of thorough searching and observing. Filters don’t help much — only rarely have I used a narrow bandpass ﬁ lter to increase contrast in certain views. Surprisingly, aperture doesn’t have much impact — if any- thing, smaller to medium aperture is often better. At right is a comparison of M51, the Whirlpool Galaxy, in three tele- scopes where the aperture doubles, then doubles again: a 6-inch, a 13.2-inch, and a 25-inch. Note that the 6-inch detects a broader area of galactic cirrus but lacks detail near the galaxy itself. The 13.2-inch and 25-inch views are very similar, differing only in image scale, with the galactic cirrus perceived as equally bright in both telescopes. The view in the 6-inch stretches all the way to M63, whereas the view in the 25-inch has enough room for a large M51 and the crisscrossing galactic cirrus of the Milky Way even at low power. All three views through the eyepiece astonish me equally — I cannot pick a favorite. Dwarf galaxies are a good match for galactic cirrus in that they are approxi- mately the same brightness. Curiously, to my eye there’s a difference in hue. Sometimes I’ll see the galactic cirrus before I detect the dwarf galaxy — this is the case with the Draco Dwarf Galaxy. In fact, on occasion I’ll trace my way to the dwarf galaxy by follow-

My first Magazine Sky & Telescope - 04.2019 | Page 60