Sky & Telescope - USA (2020-01)

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FROM OUR READERS

“

Ted Forte’s “Favorite September Sights”

(S&T: Sept. 2019, p. 30) features a plan-

etary nebula in need of a name. From

what I see in it, NGC 6781 in Aquila

could be called the “Hot Blue Alien.” I

see a face clearly: two eyes looking to

the right, a thin nose in between, two

eyebrows, and just a hint of a smile

along the color boundary at lower right.

Once I noticed those details, I cannot

ignore them. Do others agree?

Gregg Paris • San Clemente, California

Getting the Light Right

Igor Palubski and Aomawa Shields’s

article on the factors to consider when

determining if a planet orbiting a red-

dwarf star could harbor life (S&T: Aug.

2019, p. 34) makes me wonder if we

need to consider additional variables

when determining where life can exist

in the universe.

A point about the upper caption on

page 37: Although a greater fraction of

the radiation emitted by a red dwarf is

indeed in the infrared range, the total

amount of its infrared light is less — not

more — than that emitted by hotter

stars such as the Sun. The blackbody

radiation diagram itself makes this

comparison clear.

Douglas Warshow

Ann Arbor, Michigan

The fi rst sentence in Palubski and

Shields’s article misleads readers by

stating that the Sun is a “bright yellow

star.” That is not true, as every astrono-

mer knows full well. The Sun is actu-

ally a pure-white star; it only gives the

appearance of being yellow when viewed

from ground level here on Earth.

Edward S. Craig

Bangor, Maine

Camille Carlisle replies:This

is a point of linguistic discomfort

among astronomers. The Sun does

appear whitish to our eyes, and solar

astronomers will describe it thusly. But

the Sun’s emission peaks at a wavelength

around that of visible yellow. So when

discussing the Sun in the context of where

it fi ts in with other stars, astronomers refer

to it (and other G-type stars) as yellow.

The H-Alpha Universe

I thoroughly enjoyed the article about

the MDW Sky Survey (S&T: Oct. 2019,

p. 20), and I wish Dennis di Cicco and

Sean Walker success in completing such

Fun with Names

p A 13-second exposure at ISO 1600, shot

using a 100-mm f/10 refractor, easily reveals

bluish Neptune. Triton is just to its lower right.

6 JANUARY 2020 • SKY & TELESCOPE

NGC 6781

When someone discovers a comet, it’s

named after that person. Unfortunately,

this is not the case for most deep-sky

objects. So I would like to suggest that

we give credit to those who fi rst noted

signifi cant galaxies, clusters, and nebu-

lae. In each of the following examples,

most of which already have common

names, the discoverer found only one

object of each type (OC stands for open

cluster, GC for globular cluster, and PN

for planetary nebula):

Aratos’ OC M44, Aristoteles’ OC

M41, Al Sufi ’s galaxy M31, Cacciatore’s

GC NGC 6541, Cassini’s OC M50, de

Chéseaux’s nebula M17, Flamsteed’s

OC NGC 2244, Harding’s PN NGC

7293, Caroline Herschel’s galaxy NGC

253, Hodierna’s galaxy M33, Hodierna’s

nebula M8, Ihle’s GC M22, Kirch’s OC

M11, Kirch’s GC M5, Koehler’s OC

M67, Lacaille’s galaxy M83, de Mairan’s

nebula M43, Mechain’s nebula M78,

Mechain’s OC M103, Peiresc’s nebula

M42, and Webb’s OC IC 4756.

Glen Cozens

New South Wales, Australia

an amazing project! There have been

professional hydrogen-alpha surveys in

the past, but these have concentrated

more on the galactic plane. A truly all-

sky survey is bound to uncover a popu-

lation of previously unknown planetary

nebulae.

An equally interesting project would

be an all-sky survey in the light of dou-

bly ionized oxygen (O III), which would

surely reveal many faint unknown

nebulae. Indeed, amateurs have discov-

ered hundreds of new planetaries in

the past decade, and some of them are

chronicled at planetarynebulae.net/en.

Sakib Rasool

Rochdale, United Kingdom

Nabbing Neptune

Thank you for the article “Cool Hunt-

ing” (S&T: Sept. 2019, p. 48)! It reminded

me that, despite my being a stargazer for

more than 40 years, I had never tried to

spot Neptune. Possibly this was because

it had long been low in the southern sky

and didn’t seem to be a promising object

at all when observed from my latitude

of +53½°.

But after reading the article, and

with Neptune now at a more accessible

declination of –6°, I decided to give

it a try. The sky was a bit hazy on the

evening of September 21st, and moder-

ate light pollution from the small town

where I live was obvious. But after some

star-hopping with my 100-mm f/

refractor, I found that tiny bluish dot.

Then I took a picture with my DSLR

camera, which revealed a small dot