From the November 2015 issue

Kneaded erasers

Celestial sketcher Erika Rix uses kneaded erasers to create the perfect astronomical smudges.
By | Published: November 23, 2015
When comparing the versatility of erasers, the kneaded variety wins my vote every time. Among its attributes, two stand out above the rest — pliability and tackiness. It has the consistency of putty so that you can mold it to tackle even the smallest areas. And due to its absorbing nature, you can lift lightly applied graphite from the sketch without damaging the paper. This combination lets you perform the gradual fading and precise erasures that are key to creating detailed drawings. Let’s talk about small areas first.
Sketch of NGC 2022
The author sketched NGC 2022 as seen through a 16-inch f/4.5 reflector on a non-tracking Dobsonian mount, using an Oxygen-III filter and a 13mm eyepiece with a 2x Barlow for a magnification of 281x. She sketched both targets using 3.25-inch diameter circle templates printed on white paper along with a black super-fine felt tipped pen for the brightest stars, a #2 pencil, a 0.5mm mechanical pencil, and a blending stump for nebulosity and stippling unresolved stars in the globular cluster. She used a kneaded eraser to define and shape the objects by removing excess graphite. The sketches have north at the top and west to the right.
All sketches/photos: Erika Rix
There’s a striking 12th-magnitude planetary nebula, NGC 2022, nestled near the head of Orion the Hunter. You will be able to spot it at 100 power through small- to medium-sized instruments as a grayish 25″ disk on an imaginary line from Lambda (λ) Orionis to Betelgeuse (Alpha [α] Orionis). Bumping the magnification to 275x reveals a defined ring structure with a hazy center. Larger scopes show a south-southwest to north-northeast elongation with brightened western and eastern edges. Simply for fun, see if you can spot a kite-like asterism flying just northeast of the disk.

While making my sketch, I found it necessary to remove excess graphite from within the ring in order to represent the gauzy center — remember that when using graphite on white paper for deep-sky objects, you’re creating a negative sketch where starlight appears dark on a light background. After kneading the eraser to soften it, I molded it into a pointed tip. Then, with light pressure, I dabbed the tip inside the ring until I’d lifted sufficient graphite from that area to match the eyepiece view. Simply fold the eraser into itself to refresh it as needed.

Sketch of M79
The author captured this view of M79 with a 6-inch Ritchey-Chrétien telescope on a German equatorial mount, using an 8mm eyepiece for a magnification of 171x.
Next, I’ll use M79 in Lepus to demonstrate a technique called subtractive drawing. I captured the distinct shape of this winter globular cluster by removing graphite from the paper with a kneaded eraser, as opposed to adding it with a blending stump.

Nearly 4° south of Nihal (Beta [β] Leporis), this fuzzy 8.7′-wide cluster shines at magnitude 7.7 with a dense core, appearing comet-like through small telescopes. You may even resolve a few stars near its halo. Train a medium- to large-sized instrument on M79, though, and you can expect to pick out over 40 stars, along with a strand running along its eastern edge and another reaching 4′ south.

Kneaded eraser
The author molded the kneaded eraser she used for M79 to precisely erase areas of the globular cluster, form its unique shape, and lift graphite to achieve tone nuances.
Globular clusters rarely have an even shape when you observe them closely. I created a patch of dense graphite for the core of the cluster and used a blending stump to spread it outward for the halo. Once I added the stars, I molded the eraser to form a thin tip and then gently rubbed away the graphite to draw the cluster’s distinct shape. Because I had plotted the stars with hard pencil pressure, the process left these smaller points intact.

When it comes to kneaded erasers’ value for astronomical sketching, the two examples I’ve provided only scratch the surface. I’ll leave it to you to explore it further during your own nights under the stars.