Space Friday: Milky Way’s Diminishing View, Perseid Meteor Shower, and Io’s Atmosphere

Measuring Light Pollution

Earlier this summer, scientists announced that one-third of the global population—including 80 percent of Americans—cannot see the Milky Way due to artificial lights. “We’ve got whole generations of people in the United States who have never seen the Milky Way,” says Chris Elvidge, a scientist with NOAA. “It’s a big part of our connection to the cosmos—and it’s been lost.”

Elvidge and colleagues developed a global atlas of light pollution using high-resolution satellite data and precision sky brightness measurements. The team found that light pollution is most extensive in countries like Singapore, Italy and South Korea, while Canada and Australia retain the most dark sky. In Western Europe, only small areas of night sky remain relatively undiminished, mainly in Scotland, Sweden and Norway. Despite the vast open spaces of the American west, almost half of the U.S. experiences light-polluted nights.

The new light pollution atlas will be an important tool for studying artificial light as an environmental pollutant with potential health and ecological consequences. Unnatural light can confuse or expose wildlife such as insects, birds, and sea turtles, often with fatal consequences. And there are many concerns on its effects on human health, as well.

“I hope that this atlas will finally open the eyes of people to light pollution,” says lead author Fabio Falchi from the Light Pollution Science and Technology Institute in Italy. Falchi has a new book on the subject, too.

Ashley Fuller of the University of Nottingham presented another related tool in June—a light, low-cost system, deployable on a drone, that could help everyone monitor and control light pollution. The undergraduate and his colleagues envision it being used by national park rangers carrying out their work on site or students as an astronomy project.

“The night sky is a vital part of our heritage, and one we should strive to protect,” he says. “With a drone-mounted autonomous system, we can quickly gather the evidence we need to show where the problem is worse, and on a more positive note, find out where people can see the best views of the stars.”

You can get involved in light pollution monitoring and solutions, too. Head over to the International Dark-Sky Association to find out how! –Molly Michelson

The 2016 Perseids… Twice as Nice?

One of the year’s best meteor showers is already in progress—but don’t worry, you haven’t missed the best part. Always a treat for summertime campers, the Perseid meteor shower technically began on July 13, when Earth entered the broad dust-trail that was left behind long ago by a passing comet.

Sporadic meteors are seen between two to four times per hour on a dark, moonless night; they occur when Earth runs into random particles of dust and debris scattered along its orbit. As our planet—moving 106,000 kilometers (66,000 miles) per hour—bulldozes its way through these grains of space-sand, they slam into our atmosphere and burn up due to high-speed interactions with molecules of air, causing the fast-moving streaks of light known as a “meteors” (or “shooting stars,” as many people call them). Meteor showers, on the other hand, can be more spectacular because of the concentration of dust particles found in the many comet-trails that weave through the solar system, and as Earth passes through them, more meteors than usual can be seen over a short period of time.

Comet Swift-Tuttle was discovered in 1862, and the Perseids’ relationship to it wasn’t established until 1866, but the meteor shower itself has been known since at least 36 AD, when Chinese stargazers recorded it. The Perseid dust stream is quite broad, and Earth passes through it from July 13 to August 26, giving the display plenty of time to build to a peak, when Earth is in the densest part of the dust stream. That occurs on the morning of August 12, and observers may see about 60 meteors per hour—under ideal conditions, perhaps about 80 per hour. This has led to the Perseids' being considered the Old Faithful of meteor showers and one of the most reliable displays of any year.

However, this year could be different. Some astronomers predict that Earth may encounter a denser portion of the Swift-Tuttle stream than usual, which may cause up to twice the usual numbers of Perseid meteors to be seen. However, would-be meteor-watchers should be wary of the hype surrounding this year’s display. Meteor showers, like comets, can often defy expectations either way—whether surprising observers with sudden outbursts or disappointing with an underwhelming performance.

The light of the waxing gibbous Moon will interfere with the Perseids during the earlier part of the evening, when the Moon is above the horizon, but it sets around 1:00 a.m. on the morning of the 12th, leaving a dark viewing period of several hours between then and the break of dawn. That’s when skywatchers are looking in the direction that Earth is moving into the Perseid dust stream. Learn how to observe a meteor shower and optimize your chances of seeing meteors by watching our video here.

If you can’t get out or if the weather isn’t clear enough where you are, watch a live stream webcast of the shower via Slooh.com. –Bing Quock

Io’s Atmospheric Phase-Shift 

It ain’t easy being a moon of Jupiter… The giant planet’s intense gravity stretches and pulls at you, squeezing your innards (perhaps causing you to gush noxious-smelling compounds into your atmosphere), and its intense magnetic field whips charged particles into a donut-shaped maelstrom along your orbit. Even living in Jupiter’s shadow for two hours of your 42-hour orbit changes your environment on a global scale!

At least, that’s the case for Io, the innermost of the Galilean satellites (Jupiter’s four largest moons).

We’ve known for a while about Io’s volcano-fueled, rotten-egg smell and its orbital trail of charged particles (replenished, as it turns out, by those same volcanoes). But details about Io’s atmosphere have remained unclear. Decades of observations have revealed changes in the density and temperature of Io’s thin atmosphere, but what causes these changes? And what supports the atmosphere as a whole?

To help answer some of these questions, Constantine Tang of the Southwest Research Institute (SwRI) led a team to study Io as it was eclipsed by Jupiter—basically, they observed the moon as it orbited its parent planet, slipping into and out of Jupiter’s shadow. “This research is the first time scientists have observed this phenomenon directly, improving our understanding of this geologically active moon,” said Tsang in a recent announcement.

The observation indicate that sulfur dioxide gas (the primary constituent of Io’s atmosphere) freezes onto Io’s surface when the moon passes into Jupiter’s shadow and the temperature plummets. That same sulfur dioxide sublimates directly from ice into gas when Io’s surface is warmed by sunlight coming out of Jupiter’s shadow. So basically, every 42 hours, the poor little moon’s atmosphere collapses and reforms as it makes its regular trip around Jupiter. If you’re up for digging through the journal article describing the team’s results, you can find it here.

According to John Spencer, another SwRI scientist who took part in the study, “Though Io’s hyperactive volcanoes are the ultimate source of the sulfur dioxide, sunlight controls the atmospheric pressure on a daily basis by controlling the temperature of the ice on the surface. We’ve long suspected this, but can finally watch it happen.” –Ryan Wyatt