When Wildfires Imperil Our Night Skies, See Double and Variable Stars

The bad news arrived the night of May 29th. I drove to a dark site to observe and photograph the northern lights only to discover that a pall of Canadian wildfire smoke had concealed them from view. Time-exposures revealed faint wisps of aurora in a star-sparse sky. The smoke has been with us in varying degrees every night since and doesn't look to dissipate anytime soon. To monitor sky transparency, I count the number of stars visible from a dark, rural location. On May 30th, I extricated a measly 17 stars with effort. Two nights later, my tally rose to 24.

Occasionally, the smoke thins, the stars thicken, and the daytime sky regains a healthier blue hue. Still, I fear we're stuck with this fire-induced miasma for much of the summer. While the northern U.S. is particularly susceptible to wildfire smoke because it borders Canada, winds can spread the eye-burning haze far and wide. Tongues of brown-colored smoke have dimmed the Sun along the East Coast, Central Plains, Midwest, and Appalachia. Forest fires in California further extend the burning season, making widespread smoky skies a fact of life through the early fall.

While human health effects, coupled with images of hazy cityscapes and the glaring-red noontime Sun are often reported on in the media, amateurs are keen to another facet of the issue — the wholesale disappearance of the stars. Light pollution is bad enough but add in smoke and observing gets sketchier yet. These days, I track the weather and study satellite imagery to search for a clearing.

Until the sky resumes its usual transparency, I've removed all deep-sky objects from my visual observation list except for higher-altitude globular and open clusters. Fortunately, some current targets still hold their own under poor skies. These include the Sun (both white-light and hydrogen-alpha viewing), the Moon, Venus and Saturn in the morning sky, and brighter variables and double stars. Astroph0tography with smart telescopes, while compromised, remains doable by increasing exposure times.

While seeing the Sun or Moon turn cherry-red long before either sets is an incredible sight, I miss seeing the evanescent colors of the twilight transition that add so much to the charm of a sunrise or sunset. Wildfire smoke absorbs these hues, effectively neutralizing the scene.

That said, don't miss the low-arcing Strawberry Moon on June 11th. It rises in Sagittarius a little past full phase more than 5° south of the ecliptic, at declination –29.2°, close to the southernmost extreme of its range. No full Moon will track lower across the sky for Northern Hemisphere observers this year and for the next couple decades. The event is part of the current major lunar standstill, which you can read more about in the June issue of Sky & Telescope magazine.

Double Stars for Polluted Skies

If your skies are degraded, and you're hanging your head about what to observe, let me suggest a clutch of delightful double stars located within a few degrees of the bright star Vega. I was inspired to choose Vega because on smoke-filled nights, it's one of the few stars that shines through the soup. Just point your scope at Lyra's prime luminary and star-hop from one pair to the next. As a variable-star aficionado, I also suggest X Ophiuchi, a bright, Mira-type variable located in northeastern Ophiuchus near the Aquila border. It varies from magnitude 5.9 to 8.6 with a period of 332 days. In mid-June the red giant reaches its peak at around magnitude 6.5 — perfect for smoky nights. A pair of 50-mm binoculars will help coax it into view.

Vega-centric double and multiple stars

Climate change has made fires more frequent and deadly across Canada and the western U.S. in recent years. Warmer summers coupled with less (or erratic) rainfall have parched the forests and soil, making them more susceptible to lightning and human-caused fires. Where I live in Minnesota, smoky nights were an occasional nuisance from the 1980s through the early 2000s. However, since about 2015, summertime wildfire smoke has become the norm for days and sometimes weeks on end. If you're suffering from the same, hang in there. You've got company.