Huge Asteroid 'Florence' Flies by Earth Friday: How to See It in Backyard Telescopes

The enormous asteroid Florence will zoom safely past Earth this Friday (Sept. 1), providing an opportunity for skywatchers to look at the small object in backyard telescopes.

Asteroid Florence will cruise by our planet at a distance of only 4.4 million miles (7 million kilometers) — about 18 times the distance between Earth and the moon. Florence measures 2.7 miles (4.4 km) across, making it the largest space object to pass this close to Earth since NASA started tracking asteroids in detail. The asteroid hasn't been this close to Earth since 1890, and it won't be this close again until 2500, NASA officials have said. You can learn more about Florence and its flyby in a live webcast tonight (Aug. 31) at 9 p.m. EDT (0100 GMT on Sept. 1) by the astronomy broadcasting service Slooh:

According to Sky & Telescope magazine, the asteroid should now be easily visible in telescopes. The moon reached its first-quarter phase on Tuesday (Aug. 29), so its brightness will only slightly wash out Florence's reflected light. [In Photos: Potentially Dangerous Asteroids]

"Despite some interference from moonlight, 3122 Florence should be fairly easy to spot in even modest backyard telescopes," Kelly Beatty, a senior editor at Sky & Telescope magazine, said in a statement.

The huge asteroid 3122 Florence appears as a bright dot (center) in this photo taken with a large amateur telescope on Aug. 28, 2017, by Gianluca Masi of the Virtual Telescope Project. At the time, Florence was about 5 million miles (8 million kilometers) from Earth. The long vertical streak at left is the geostationary satellite AMC-14. (Image credit: Gianluca Masi/Virtual Telescope Project)

When to see asteroid Florence

The best time to see asteroid Florence will be in the late evening, when it's positioned well overhead, according to Sky & Telescope. Peak brightness will be tonight (Aug. 31), when it's at magnitude 8.7. However, the asteroid should be almost as bright for several days before and after the end of the month. [Famous Asteroid Flybys in History (Infographic)]

You can also watch the asteroid online in this free webcast from the Virtual Telescope Project, which is led by astrophysicist Gianluca Masi. The webcast will begin today at 3:30 p.m. EDT (1930 GMT).

Another good time to watch is Saturday (Sept. 2) at about 8 p.m. EDT (0000 GMT on Sept. 3). The asteroid will pass by four fourth-magnitude stars at the head of the constellation Delphinus, the dolphin, according to Sky & Telescope. 

Florence's path in the night sky will move north by a little less than the full moon's diameter every hour. Within just a few minutes of observing, you should see the asteroid move in a telescope.

Sky & Telescope has detailed charts to help with locating 3122 Florence. In general, over several days, the asteroid will move roughly from south to north, and will pass through the constellations Capricorn, Aquarius, Delphinus, Vulpecula and Cygnus. 

This sky map by Sky & Telescope magazine shows the location of the asteroid 3122 Florence as it moves across the night sky in late August and early September 2017. The asteroid will fly within 4.4 million miles (7.1 million km) of Earth on Sept. 1. (Image credit: Sky & Telescope Magazine diagram)

An asteroid called Flo

Asteroid 3122 Florence was discovered in 1981 by astronomer Schelte "Bobby" Bus at the Siding Spring Observatory in Australia. The asteroid is named in honor of Florence Nightingale (1820-1910), who pioneered modern nursing, NASA officials said in a separate statement.

Weather permitting, Florence will be visible in telescopes as a ninth-magnitude object. "Magnitude" refers to the brightness of an object; lower magnitudes are brighter. Florence will be a little dimmer than Neptune (magnitude 8), and well below the threshold visible to the naked eye (magnitude 6). The brightest planet, Venus, can get as bright as a brilliant magnitude -5. 

The asteroid is relatively bright because of its large size and because its surface reflects roughly 20 percent of the sunlight that hits it, according to Sky & Telescope. (For comparison, the moon reflects only 12 percent.) Astronomers think that Florence is nearly spherical because its brightness changes only a little during its 2.4-hour rotation. 

Editor's Note: If you capture a great image of asteroid Florence moving across the sky and would like to share it with and our news partners, send photos and comments to

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Elizabeth Howell
Staff Writer, Spaceflight

Elizabeth Howell (she/her), Ph.D., is a staff writer in the spaceflight channel since 2022 covering diversity, education and gaming as well. She was contributing writer for for 10 years before joining full-time. Elizabeth's reporting includes multiple exclusives with the White House and Office of the Vice-President of the United States, an exclusive conversation with aspiring space tourist (and NSYNC bassist) Lance Bass, speaking several times with the International Space Station, witnessing five human spaceflight launches on two continents, flying parabolic, working inside a spacesuit, and participating in a simulated Mars mission. Her latest book, "Why Am I Taller?", is co-written with astronaut Dave Williams. Elizabeth holds a Ph.D. and M.Sc. in Space Studies from the University of North Dakota, a Bachelor of Journalism from Canada's Carleton University and a Bachelor of History from Canada's Athabasca University. Elizabeth is also a post-secondary instructor in communications and science at several institutions since 2015; her experience includes developing and teaching an astronomy course at Canada's Algonquin College (with Indigenous content as well) to more than 1,000 students since 2020. Elizabeth first got interested in space after watching the movie Apollo 13 in 1996, and still wants to be an astronaut someday. Mastodon: