Sky & Telescope - October 2020 - 31

T At home at latitude 49° north Messier 15 is the beauty that my 16-inch
spends the second-most time on, right after M13. At 261×, an O III filter revealed the challenging 3″ planetary nebula Pease 1 hiding only 25″ northnortheast of M15's center. The 13th-magnitude prize requires a starhop
within the globular (see S&T: Oct. 2000, p. 132).
Another of my club's members, Jim Failes, had an 8-inch Dynamax SCT
that at 120× showed five arcing star chains and M15's impressive nucleus.

"There is a three-dimensional appearance to M15 - like the classic
volcanic cone of Mount St. Helens before it blew."
Through Goldendale Observatory's 24.5-inch Cassegrain at 180× M15's
core rises to an amazingly bright tiny nucleus, similar to that of the Pavo
Globular, and dominated the view. A dark spot, only about 0.3′ in diameter,
lies midway from the nucleus to the edge of the core. In a 25-inch Dob I
noted that the nucleus is offset to the northern side of the teeming core.

S Eighth place goes to Messier 5, the brightest globular north of the celestial equator, and
Concentration Class V (see Tipbox) like M13. My
8-inch shows far fewer stars in M5 than it does in
M13 or M92, but my logbook entries made with
15-inch and larger scopes use words like "glory,"
"spectacular," and "superb." My finest view of M5
was on a pristine night with my 16-inch at 261×.
The stars were crisp tiny points and were easily
resolved right across the central globe with a fairly
bright star near the center. A small dark vacancy
lurks on the northeastern edge of the central mass,
elongated northwest to southeast. The five main
star chains arise on the northwestern side of the
core, and then flow back around the core to the
south through the east side of the halo.

Concentration Classes
In 1927, Harlow Shapley and his
graduate student Helen Sawyer
(later Sawyer Hogg) classified all
known globular clusters according
to apparent concentration of stars
toward the center. The 12 classes,
assigned Roman numerals (although
some references denote them using
Arabic numerals) range from I, which
represents the highest concentration of
stars toward the center, to XII, the most
loosely packed of the globular clusters.
The sample featured here represents all
classes, with the exception of X and XII.

sk yandtelescope.org * OCTOBER 2 02 0

31



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Sky & Telescope - October 2020

Table of Contents for the Digital Edition of Sky & Telescope - October 2020

Contents
Sky & Telescope - October 2020 - Cover1
Sky & Telescope - October 2020 - Cover2
Sky & Telescope - October 2020 - 1
Sky & Telescope - October 2020 - Contents
Sky & Telescope - October 2020 - 3
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