Sky & Telescope - February 2022 - 11

SPACE & SOCIETY
Pittsburgh Goes Dark; Could It Start a Trend?
CAN YOU SEE the Milky Way from
your home? Diane Turnshek can, and
she wants Pittsburgh to see it, too.
Turnshek (Carnegie Mellon University)
helped draft the Pittsburgh City
Council's new Dark Sky Ordinance,
which covers the city's parks, facilities,
and streetlights. The new ordinance
would replace 35,000 old high-pressure
sodium streetlights within the next
three years. All of them will be darksky-friendly,
with cut-off fixtures that
direct light where it needs to go.
Crucially, the ordinance also replaces
4,297 newer LED streetlights, the
bright, blue-white kind that were hastily
installed in cities across the world in
the 2010s. Turning night into day, these
high-temperature LEDs are now a leading
cause of the world's growing light
pollution. Pittsburgh will replace these
with lower-temperature LEDs, which
have become cost competitive.
The new plans also include placing
between 3,000 and 15,000 new LED
streetlights, which the city found necessary
during the analysis. These will also
be dark sky-friendly: motion-sensored,
shielded, and with both a lower wattage
and cooler temperature.
Part of the preparatory work included
making a nighttime map of Pittsburgh's
58 square miles. Turnshek and colleagues
undertook this effort using
drones and a Sony DSLR camera under
a Cessna aircraft on clear, snowless, dry,
and moonless winter nights. Astronauts
on the International Space Station also
took photos.
Pittsburgh's ordinance isn't specifically
related to the needs of astronomers.
Rather, its stated aims are to
improve safety and security, reduce light
pollution, save energy, and advance
equity in all Pittsburgh neighborhoods.
" The new Pittsburgh ordinance is
pThe Phipps Conservatory and Botanical
Garden, photographed from above via drone, is
one of the organizations that has signed on to
Pittsburgh's dark-sky ordinance.
not quite as restrictive as Flagstaff or
even Tucson, " says John Barentine (now
at Dark Sky Consulting), naming two
cities where the needs of professional
astronomical observatories are taken
into account. " But for major U.S. cities,
especially those on the East Coast, it is
quite a bit better than others that are
out there - I think this is the future of
outdoor lighting policy in the U.S. "
¢JAMIE CARTER
IN BRIEF
Jupiter Whacked Again
Get your scorecards out - Jupiter took
another interplanetary hit on October 15th,
the 11th observed in modern times. A month
after amateurs recorded a different flash (S&T:
Jan. 2022, p. 10), a team led by Ko Arimatsu
of Kyoto University captured this most recent
flare at infrared and visible wavelengths.
Another Japanese observer, who goes by the
Twitter handle yotsuyubi21, and Victor PS Ang
of Singapore confirmed the impact. Arimatsu
and his group used a surveillance system,
part of the Organized Autotelescopes for Serendipitous
Event Survey (OASES), to record
the burst, which lasted about four seconds.
According to the Europlanet Society, every
year an average of 6½ objects hit Jupiter in
impacts big enough for amateurs to record.
Aided by transient-alert software like DeTeCt
(S&T: Jan. 2022, p. 52), we've seen a steady
uptick in the number of observed impacts,
proving that the more we look, the more we
see. Neither of the two recent impacts made
dark scars on Jupiter's cloudtops.
¢BOB KING
See images and video at https://is.gd/
Jupiterimpact11.
Lucy Launches to the Trojans
NASA's Lucy mission launched on October
16th to explore Jupiter's Trojan asteroids (see
page 12), which serve as pristine examples
of the early solar system. The launch was
flawless and the solar panels deployed as
expected and are generating power, but
one of the panels did not latch correctly.
Nevertheless, the mission is continuing to a
heliocentric orbit. After an Earth flyby in late
2024, Lucy will visit one main-belt asteroid
(52246 Donaldjohanson) in 2025 and seven
Trojan bodies between 2027 and 2033 (with
an additional Earth flyby in 2031). The Trojans
have likely been trapped in their current orbits
for billions of years, so they are representative
of material left over from the formation
of the solar system. Lucy will investigate the
geology and composition of the rocks to shed
light on planet formation processes. The Lucy
team is looking for motivated observers to
follow occasions when target asteroids occult
background stars. Such observations can
help improve estimates of their shapes and
orbits. Unistellar also has ongoing asteroid
occultation campaigns.
¢DAVID DICKINSON
See upcoming events at https://is.gd/
Lucyocc and http://is.gd/Unistellarocc.
Two Hits Made the Moon
Scientists have long thought that the Moon
formed when a Mars-size protoplanet
(dubbed " Theia " ) hit newborn Earth. Now a
study in the October Planetary Science Journal
suggests that the protoplanet hit Earth
not once but twice. The first time, Theia only
glanced off Earth. Then, some hundreds of
thousands of years later, it came back to deliver
the final, Moon-generating blow. Erik Asphaug
(University of Arizona) and colleagues
simulated the impact 1,000 times and found
that a " hit-and-run return " scenario could help
answer two longstanding questions around
the Moon's origin. First, Theia had to come
in at the right speed: too fast and it would
have exploded, too slow and the Moon's orbit
would look different. The one-two punch puts
Theia's speed between these extremes. The
first, glancing impact would have slowed it
down for the second one. The hit-and-runreturn
scenario also addresses unexpected
similarities between the Moon's and Earth's
compositions, because two impacts would
have enabled more mixing. While the simulations
don't quite match the observed compositions,
the team argues that more advanced
models would yield even better results.
¢ASA STAHL
sk yand tele scope .o r g * FEBRUARY 2022 11
MICHAEL LINCOLN AND DIANE TURNSHEK
https://is.gd/Jupiterimpact11 https://www.is.gd/ http://www.is.gd/Unistellarocc https://is.gd/Jupiterimpact11
Sky & Telescope - February 2022

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