Sky & Telescope - December 2022 - 66

S&T Test Report
deep-sky objects started to reveal smallscale
detail. Using a Tele Vue Nagler
12-mm eyepiece (100×), globular clusters
M13 and M22 were easily resolved
into myriad stars all the way to their
cores. Bright galaxies M81 and M82
began to look like individual galaxies
rather than the vague, amorphous glows
presented through smaller apertures.
The f/4.7 parabolic mirror is a focal
ratio that is long enough that coma isn't
very noticeable except at the extreme
edge of the field of view. Star images on
either side of focus were identical as I
racked through focus.
The Ease of StarSense
The StarSense Explorer 10-inch Dobsonian
is a good telescope, but what
sets it apart from the pack is its clever
StarSense dock. This plastic smartphone
cradle attaches to a mounting
foot near the focuser, where a finder is
typically located. The dock contains a
rectangular mirror that faces skyward
at a 45° angle from your smartphone's
camera. The phone is held in place
with a spring-loaded clamp, and its
position is adjustable in three axes to
allow the phone's camera to take in the
maximum area of sky. The dock itself
attaches to the scope with a tapered
dovetail and is secured with two locking
thumbscrews to ensure repeatable
alignment. A removable cover protects
the mirror when the dock is not in use.
After assembling the telescope and
aligning the red-dot finder, I downloaded
the StarSense
Explorer app from the
iOS App Store for my
iPhone 8. (Android
users can get the app
from the Google Play
site.)
When first opened,
the unique unlock code
on a provided card
needs to be input. (You
can install the app on
up to five devices with
the same code.) Next,
the app tells you to
" center camera over
mirror, " which is done
by adjusting the knobs
on the dock until you
can see as much sky as possible on your
phone's screen. When satisfied with the
view, tap Next to enter the pointing
alignment mode. Forget about a typical
multi-star alignment, or even the
single-star alignment routine originally
required with the first StarSense
Explorer scopes we reviewed in 2020.
Simply aim the scope at a distant terrestrial
object (such as a treetop or
building) and center it in the eyepiece.
You then drag the app's on-screen
crosshairs until they're on top of your
target and tap Done. That's it - you're
ready to observe! This initial alignment
can conveniently be performed
any time, day or night. The alignment
doesn't need to be done again unless
you change the position of the phone
Top: Each of the 18-cmdiameter
plastic altitude
bearings on the OTA has a
tension-adjustment knob on
a threaded bolt, surrounded
by a smooth plastic bushing
that drops into slots on top
of the rocker box. Bottom:
Two plastic knobs mounted
inside on both sides of the
rocker box uprights form the
bearing surfaces for smooth
altitude motion.
in the dock, or switch
smartphones.
You'll need a fairly
large, unobstructed
swath of sky overhead
for the app to get its
bearings. Buildings or
trees blocking large portions of the sky
can prevent StarSense Explorer from
successfully plate solving. It also needs
to be rather dark before the app can
recognize stars in the images recorded
with the phone's camera. StarSense
was able to recognize fields with bright
stars overhead by the start of nautical
twilight, but not much earlier. Likewise,
searching for an object that may be
washed out by a bright Moon sometimes
triggered an onscreen warning
about moonlight.
Pointing the telescope skyward
after alignment brings up a pleasing
graphical view of the sky, similar to the
one in the SkySafari planetarium app.
(Simulation Curriculum, the same company
behind SkySafari, developed the
Celestron app.) StarSense Explorer contains
the entire Messier and Caldwell
catalogs in the app's " common objects
lists, " plus thousands of objects in the
Abell, Barnard, Sharpless, NGC, PGC,
IC, and UGC catalogs.
Tapping the star on the bottom of
Left: A tapered dovetail interface attaches the StarSense Explorer dock securely to the permanently
attached mounting foot on the 10-inch StarSense Explorer Dob. Right: The author's iPhone
8 is mounted with its lens aimed into the dock's mirror. Three precision rack-and-pinion motions in
the dock allow the precise positioning of a wide range of smartphones.
66 DECEMBER 2022 * SKY & TELESCOPE
the app screen opens a list of " tonight's
best objects " and tells you if the object
is " city viewable " or " dark sky viewable. "
Each object in the list is also
circled in blue on the sky chart. Tapping
on an entry in the list brings up plenty
of other information, and for many
objects there's a calmly narrated audio
description. Tap on the " locate " icon
and within moments a message pops up

Sky & Telescope - December 2022

Table of Contents for the Digital Edition of Sky & Telescope - December 2022