Sky & Telescope - February 2023 - 21

NGC 457: RON BRECHER; NGC 2169: GARY IMM;
GREEN LASER: NPS / WILLIAM PEDRO
N
WHAT DO YOU SEE? Asking your audience what they see in patterns
in the sky is a great way to stimulate their interest. Before you tell them
that NGC 457 is also known as the Owl or E. T. Cluster, ask them what
the open cluster looks like to them.
viewer has trouble with it, try framing the cluster in your
finderscope; it'll be more apparent in the wider field.
When groups of astronomers convene to do a public event,
they often concentrate on the same celestial showpieces - this
can become a little boring for your guests making their rounds
between scopes. You'll do well to compile a collection of objects
that make successful outreach targets by introducing some
variety. Almost any of the Messier clusters are usually good
choices. One of my favorites is M46 in Puppis. You can challenge
your observers to detect the planetary nebula NGC 2438
that seems to float among the cluster's stars. The European
Space Agency Gaia satellite's measurement of NGC 2438's
distance puts it at 1,370 light-years, far closer than the star
cluster, which lies about 5,000 light-years from us.
At sidewalk astronomy events, we often only get one chance
to capture the interest of the casual passerby. The target you
choose should be impressive. The Perseus Double Cluster,
comprising NGC 869 and NGC 884, is a sure-fire crowd
Green Laser Pointers
Laser pointers can do considerable
harm to eyes and skin, and they should
not be considered toys or be used by
minors. The greater the output power
of your laser, the more likely it is to
cause injury. Laser pointers must be
less powerful than 5 mW - when
they're brighter than that, they're
known as overpowered. Consumers
should be aware that many commercially
available lasers are not labeled
and may even be mislabeled. The Food
CELESTIAL DIGITS If you've ever seen the open cluster NGC 2169
through a telescope, you'll likely remember your initial reaction. Eliciting a
chuckle from your guests at the eyepiece can also be a satisfying experience
for the scope owner.
pleaser. It's a particularly good target if your outreach setup
includes a wide-field instrument like mounted binoculars or
a rich-field telescope. You'll want at least a 1° field of view to
adequately frame the pair of open clusters.
The western cluster, NGC 869, contains a beautiful asterism
called the Diamond Ring. A 6.6-magnitude star near the
center of the cluster is set off by an arc of five fainter stars
that opens toward it, vaguely resembling an engagement ring.
Asking viewers to seek this out will encourage them to look
more closely and consider what they see.
Pointing out that the Double Cluster is visible to the naked
eye under dark skies and that it has been known since antiquity
is a good segue into the subject of ancient stargazing and
the lore surrounding the constellations. The Double Cluster
marks the head of the Greek hero Perseus.
In some depictions, it represents
the scimitar with which he slew the
Medusa, a winged female creature
and Drug Administration reports that
60% of lasers tested have greater output
than their labels indicate. As a rule
of thumb, if your pointer is small and
runs on button batteries, it's probably
less than 5 mW. A pen-size or larger
laser that runs on AA or AAA batteries
is likely too bright. Some states
prohibit the use of green laser pointers
by minors and in certain situations, like
on school grounds. They should never
be aimed at a passing aircraft or at a
person. Many
major star parties
prohibit their use
because of the danger
of eye damage and the spoiling effect
they can have on astrophotography.
As the use of laser pointers is strictly
controlled or even illegal in some jurisdictions,
make sure to check with your
local astronomy club to find out what
rules apply locally. See https://is.gd/
laserpointers for more tips.
sk yand tele scope .o r g * FEBRUARY 2023 21
https://is.gd/laserpointers https://is.gd/laserpointers http://skyandtelescope.org
Sky & Telescope - February 2023

Table of Contents for the Digital Edition of Sky & Telescope - February 2023
