Two weeks ago we tracked down the distant planet Uranus in Aries the ram. Not a dozen degrees away a much smaller member of the solar system plies the sky — asteroid 8 Flora. Flora orbits within the inner edge of the main asteroid belt between Mars and Jupiter. It was discovered in October 1847, a time when asteroids were still called planets. As more and more were discovered it soon became apparent that they differed from the large, classical planets. All of them were so small they looked exactly like stars through the telescope, so astronomers adopted the term asteroid (star-like) to describe them.
Flora was the 8th discovered, the reason it's full name is 8 Flora. These days, discoveries continue apace with more than 822,000 asteroids known. Flora's the largest, inner main belt asteroid with a diameter of about 91 miles (147 km) or about the size of Connecticut. Its name has a familiar ring because Flora is the Latin goddess of flowers and gardens.
Both Flora and Uranus were at opposition and closest to the Earth on Halloween. While you can glimpse Uranus with the unaided eye from moonless, rural skies you'll need binoculars to see Flora. It shines brightest right now at magnitude 8.1. Uranus is an easy catch in binoculars even under light-polluted skies, Flora less so. I spotted it in 8x40 binoculars on Oct. 26 with a bright moon out. Now that the moon is waning and rising later, better viewing opportunities lie ahead.
You'll find Flora traipsing across the head of Cetus the sea monster this month. It starts out at magnitude 8.1 but fades a little to 8.8 by month's end, so try to catch it in the next week when it's brightest.
Uranus is so distant it moves very slowly across the sky compared to the relatively zippy asteroid. When you first find Flora in binoculars you'll see its westward movement when you return 2-3 nights later. A telescope will easily reveal its motion in just a day.
Flora moves westward across Cetus in the direction of brilliant Mars. A good way to find it is to start at Mars and measure off three fists to the left to arrive at Menkar. Menkar is the second brightest star in Cetus and equal in brightness to the Big Dipper stars. Point your binoculars at it and focus until the star is a tiny point, then star-hop about one binocular field back towards Mars (west) and identify Flora using the chart.
It'll look exactly like a faint star. A telescope will make it appear brighter, but no matter what magnification you use Flora won't show a shape — at 81.6 million miles (131.4 million km) away it's just too teeny.
That doesn't mean astronomers don't have ways to eke out a shape. When an asteroid passes near the Earth, they use radio telescopes to beam radio waves at the target and derive its shape and surface features from the returning echoes. Flora's too far away to use this technique. Instead, scientists study how Flora's light varies as it rotates and use that information to model an approximate shape. That's how we know that Flora is roughly spherical.
We also know through study of the light reflected from its surface that the asteroid is rich in once-molten rock. Planetary scientist Michael Gaffey's (Univ. of North Dakota) study, published in Icarus, indicates that Flora is likely the "residual core of an intensely heated, thermally evolved, and magmatically differentiated planetesimal which was subsequently disrupted. The present surface samples layers formed at and near the core-mantle boundary in the parent body."
That's a mouthful, but the bottom-line is this: Flora appears to be a chunk of a larger asteroid that was disrupted by an impact. This makes sense because it's the largest member of the Flora family, a group of more than 13,000 asteroids that share similar orbits. Whoa — that's a lot of relatives!
I hope you get a chance to see this wandering rock the next clear night. I know binoculars can be shaky to hold. If you can't fix them to a tripod, try holding them against the side of your parked car, a post or the wall of a building. The less shake the easier it will be to see it. And while you're in the neighborhood stop by for a look at Uranus, too.
"Astro" Bob King is a freelance writer for the Duluth News Tribune. Read more of his work at duluthnewstribune.com/astrobob.