Night Sky On The Fourth Of July

Fireworks on the 4th of July. Credit: Bob King

Today we celebrate American Independence Day, when lots of us will be out watching fireworks displays at dusk. Since getting a good seat means arriving early, you might have a little time on your hands to look around and take in the stars before the show begins. Or even after the show. Assuming a forecast of clear skies,  I’ve prepared four sky scenes to help you identify what’s up tonight. If you’re a parent, take your phone along and use the maps here to help you point out the sights with your young ones.

The waxing gibbous moon will be the first thing to catch your attention. It stands a fist and a half to the upper right of the twinkly red star, Antares in Scorpius. Antares’ distance of nearly 550 light years hides the fact that it’s almost 900 times as large as the sun. Another 1.5 fists directly to the left of Antares sits Saturn, the only planet with a set of bright rings you can see in even a small telescope. It’s a full magnitude brighter and pale yellow.

South is where most of the action will be tonight with the moon, two bright planets and two bright stars, Antares and Arcturus. Created with Stellarium

The moon conveniently helps us identify the four compass directions tonight. It’s due south around 10 p.m. local time. Face it and north is to your back, east to your left and west to your right.

Now, shift your gaze to the southwest. About a third of the way from the horizon to the overhead point, you’ll see a bright “star”. That’s Jupiter. On July 10, NASA’s Juno spacecraft will make a close pass of the planet’s Great Red Spot and take the most detailed photos ever of that bigger-than-Earth hurricane. Continue a fist to the left of Jupiter to spot fainter Spica, the brightest star in the zodiac constellation, Virgo the Virgin.

Few bright stars dot the western sky, but you may still find Regulus. Created with Stellarium

If you now pivot a quarter turn to the right and face west, you can use Jupiter (now on your left) to find another bright star. Reach your fist to the sky and mark off a little more than four fists to the right and below the planet, and you might get a glimpse of Regulus, Leo’s brightest star. Once a dominant presence in the spring sky, Regulus has been sinking in the western sky since June and is now fighting for its life in the orange glow of dusk, a battle it will eventually lose.

The easy to find asterism, the Big Dipper, stands on its bowl tonight. Created with Stellarium

Turn around to face north — standing halfway up balancing on the end of its bowl you’ll spot the Big Dipper. You can easily find the North Star, Polaris, by shooting a line through the end stars of the bowl. If you’re lucky enough to have a wide open view of the northeastern sky, the W of Cassiopeia the Queen makes a pleasant sight. Cassiopeia’s more of fall and winter constellation, but it begins its climb up the airy wall of the sky in mid-summer. Seeing it on July 4 invokes memories of the chilly, dewy nights that lie ahead.

Find a beast in the east. The supergiant star Deneb marks one corner of the Summer Triangle and is also the head of the Northern Cross. Created with Stellarium

Finally, pivot ’round to face east and three bright stars arranged in a giant isosceles triangle called the Summer Triangle. Vega’s the brightest and closest star of the trio — only 25 light years away — with Deneb over 100 times farther! Can you imagine how intrinsically bright Deneb must be to still appear bright enough to hold up its end of the triangle? It’s a white-hot supergiant star more than 200 times larger than the sun and one of the most distant stars you can see without optical aid.

The Summer Triangle and Big Dipper are both asterisms, figures of bright stars within a constellation or made from the brightest stars of multiple constellation. They’re easy, shorthand shapes anyone can see.

Oops! Almost time for the fireworks show, so I’m going to bug out of here. Happy 4th!