On moonless nights, look for the not-so-bright sights among stars

Being so bright, Jupiter makes a good jumping-off point to sky sights that aren’t quite so easy to spot. For instance, look high to Jupiter’s upper right for the star Altair. They’re separated by about three times the width of your fist at arm’s length. Altair is the piercing eye of the constellation Aquila, the Eagle. You can connect the star dots of Aquila to form a sort of roosting bird with cocked head and upraised wings, as shown here. But you’ll need a dark sky to spot the full complement of stars, so try again later this week, once the moon is gone. And the farther from the city you are the better. The Eagle looks to me more like a bat, but with constellations, you take what you can get.

Left of Altair by about a fist-width is the much smaller constellation Delphinus, the leaping Dolphin. It’s fairly dim, but if you can see it at all, its distinctive little shape always makes it a celestial landmark of late summer and early fall.

Look lower left of Jupiter by about 2½fists at arm’s length, and if there are no trees or buildings in the way, you’ll spot twinkly Fomalhaut, the Autumn Star.

Look a little west of straight overhead, and there’s bright Vega, the Summer Star.

These four objects - Fomalhaut, Jupiter, Altair, and Vega - form a huge, nearly straight diagonal line. Aside from the moon, they’re the brightest four things of October evenings this year, offering proof that you can do a certain amount of urban astronomy even under very bright-sky conditions.

Bright planets such as Jupiter, for instance, are unaffected by light pollution. Nor are bright stars, if what you’re doing is teasing apart the secrets encoded in their light.

An outstanding example of bright-sky astronomy is happening on a mountain overlooking the dazzling Los Angeles basin. Mount Wilson Observatory was founded in 1904 when the city was small and outdoor lights were few. The growth of Los Angeles put an end to Mount Wilson’s glory days of determining the distances of galaxies and the expansion rate of the universe. However, its 100-inch telescope, a near-antique from 1917, has been outfitted with a 21st-century imaging system that enables it to see fine detail through Earth’s rippling atmosphere, almost as if the atmosphere weren’t there. With this setup, the telescope can image selected bright objects, such as asteroids and double stars, almost as sharply as Hubble can do from space.

Near the 100-inch telescope, astronomers have also built a cutting-edge new instrument for much sharper measurements. In 2005, the Center for High Angular Resolution Astronomy, or CHARA, at Georgia State University installed an array of six 40-inch telescopes, spread across almost a quarter-mile, connected to a central facility by vacuum pipes carrying the telescopes’ light beams. In the central building, precision machinery aligns and combines the same individual light waves coming from a star as sampled by the six widely separated telescopes. This technique, known as interferometry, requires the whole array to operate as a unit with literally microscopic mechanical precision. When everything works, the CHARA Array can resolve extremely fine detail in small, bright objects almost as if it were a single telescope nearly a quarter-mile (13,000 inches) in diameter.

In this way, the CHARA Array is mapping the actual faces of stars and directly measuring their sizes and shapes. Not all stars, it is demonstrating, are round. Altair, for instance, is spinning so fast that it’s distorted into an ellipsoid shape. In particular, the array is leading the way in measuring the precise orbits of double stars, which is the only direct way to determine stars’ masses, a foundation stone of all astrophysics.

Such work may inspire city skywatchers to do the best they can with their own bright skies.