Sky & Telescope - April 2024 - 22

Leo Targets
12h 00m
2
1
3
4
5
6
7
OGC 0032
Leo II
δ
3501
θ
β
M65
M66
ι
VIRGO
ρ
χ
ν
σ
Wolf 359
+5°
IN THE LION'S DEN While Leo, the Lion, is one of the most recognizable constellations in the sky, for owners of small- to medium-size telescopes
it offers a wealth of unique galaxies and even a few nebulae.
Planetary and Pre-Planetary Nebulae
Astronomers have identified planetary nebulae in nearly every
constellation, and Leo is no exception. But have you heard
of EGB 6? Glenn Ellis, Earl Grayson, and Howard Bond (all
then at Louisiana State University) first reported Leo's one
and only planetary nebula in 1984 - at 11′ × 13′, its unusually
large size and low surface brightness being the secret to
it escaping detection for so long. They found it by examining
paper prints of POSS plates held at arm's length!
To locate this old, 10th-magnitude planetary, look 4.2°
northwest of Regulus or about 0.8° northeast of 23 Leonis.
My first look at it came around two years ago in my 5.1-inch
reflector at 34× with the aid of a DGM Optics Narrow Pass
Band (NPB) filter. But my best view came a year ago in my
6-inch reflector since it can achieve a wider true field. At 25×
and 39×, the planetary's somewhat amorphous disk was more
distinct and slightly easier to see with the NPB filter than
with an O III filter.
Pre-planetary nebulae are short-lived and hence rare - they
represent the ephemeral phase a low- to intermediate-mass
star goes through before evolving into a planetary nebula.
22 APRIL 2024 * SKY & TELESCOPE
Astronomers identified the first examples of pre-planetaries in
the 1940s, but it was several decades before they understood
them better. The brightest in the sky is . . . you guessed it, in
Leo! It's known fondly as the Frosty Leo Nebula due to its
abundance of silica dust grains coated with ice. The Infrared
Astronomical Satellite detected it in 1983 (which is reflected
in the nebula's official designation), as pre-planetary nebulae
largely emit scattered light in the infrared and optical.
The first time I saw the Frosty Leo Nebula was in 2015,
but viewing it two years later in my handheld 8×56 binoculars
forever gave it a special place in my heart. In fact, it was
one of the first objects I looked at after acquiring my 16-inch
in 2022. With that telescope at 105×, it appeared barely
nonstellar at around 11th magnitude just 1′ southwest of a
12.6-magnitude star. But increasing to 300× revealed a very
small, high-surface-brightness glow tinged with an impressive
blue color that appeared elongated roughly north-south.
At 600×, the glow split into two cores, with the fainter one at
the northern end. I never thought to look for its ansae (extensions),
but Contributing Editor Bob King has detected the
northern one in his 15-inch Dobsonian at 400×.
EGB 6
23
M105
M95
M96
ο
UGC 5189
Regulus
α
Frosty Leo
+10°
LEO
γ
VV 689
Stan's Star
HD 92884
η
+15°
ζ
OGC 1559
+20°
URSA
MAJOR
11h 30m
ξ
LEO MINOR
κ
µ
+25°
ε
λ
11h 00m
10h 30m
10h 00m
Leo A
9h 30m
+30°
Star magnitudes

Sky & Telescope - April 2024

Table of Contents for the Digital Edition of Sky & Telescope - April 2024