A newly-discovered asteroid passes just 44,000 miles from Earth Friday. You can watch it from the comfort of your home.

Comin' our way Friday
Asteroids like the one shown in this artist's view pass near Earth at least a few times a week. Those that could pose a future threat are classified as potentially hazardous asteroids (PHAs).

Potentially hazardous and near-Earth asteroids zing through Earth's neighborhood nearly every day. Since the weekend, seven small asteroids — including two potentially hazardous ones — came within 0.5 to 16 times the distance of the Moon. The largest, 2002 AJ29, was all of 2,100 feet (640 meters) across. The work week ends with an exceptionally close approach of asteroid 2018 CB, which will skim just 44,000 miles past Earth around 5 p.m. Eastern Time (22:00 UT) Friday, February 9th.

Potentially hazardous asteroids (PHAs) are those at least 328 feet across that approach within 4.6 million miles of Earth. Because asteroid orbits can change over time due to gravitational effects from the Sun and planets, a PHA could potentially impact the planet sometime in the future.

That future looms large and distant because at least for now, no known PHA is predicted to impact Earth for at least a century. There are only probabilities, and those probabilities usually drop close to zero once astronomers can nail down a newly discovered asteroid's orbit. Astronomers determine those details by photographing the asteroid as it moves, noting its precise position with relation to the background stars. The more observations, the better we know the orbit and the better we can predict the object's future location and behavior.

Taking care of business rock by rock
This graphic shows the number of large Near-Earth asteroid discoveries by programs devoted to searching for PHAs. Notice that the number of big asteroid finds has dropped off because most of those have been discovered. There are still millions of smaller ones awaiting discovery.

How to Watch

It's a blast to track an Earth-approaching asteroid in a telescope. Even the little ones can become bright enough to spot when they're really close. Generally, the closer they are, the faster they zip across the sky. I've looked at several where I've had to nudge the tube in the asteroid's direction of motion every couple minutes to keep up. But all of these quick, come-and-go objects look like stars in even the largest telescopes. Only radar can reveal their shapes and textures.

Spirographic style
This graphic shows the orbits of known potentially hazardous asteroids (more than 1,400) as of early 2013.
NASA / JPL-Caltech

2018 CB, an Apollo asteroid, was discovered on February 4th by the Catalina Sky Survey at magnitude 19. According to NASA's HORIZONS website, it will reach a peak magnitude of 12.8-13.0 for a few hours as it speeds from Perseus through Pisces. While bright enough to spot in an 8-inch telescope, the timing is bad for the Americas, where it be late morning or afternoon. European and African observers are well-situated, with the asteroid plinking along under a dark, early evening sky.

2018 CB is on the small side, between 50 and 130 feet (15 and 40 meters) in size, a little larger than the Chelyabinsk meteoroid that broke up over Russia five years ago this month. Though only twice as distant at closest approach as the satellites orbiting in the geosynchronous belt, it will be too faint for many observers to see in smaller telescopes.

Sky map for 2018 CB
Earth-approacher 2018 CB hurries southwest from Perseus to Pisces when brightest. European and Middle Eastern observers are favored. (Click for larger version.)
Stellarium, with additions by the author

When these passers-by are too faint for amateur astronomers to track them, several websites offer live, online views from big scopes. One of those is Gianluca Masi's Virtual Telescope Project, based in Italy, which coordinates observations with Tenagra Observatories in Arizona. Masi, an astrophysicist, loves to share asteroids, eclipses, and other celestial events with as many people as possible, especially those without a telescope or clouded out by bad weather. This Friday (February 9th), he'll live stream the close approach of 2018 CB starting at 3 p.m. Eastern time (20:00 UT).

By the time darkness arrives at the East Coast, 2018 CB will have plummeted to 16th magnitude! All the more reason to check it out online at the Virtual Telescope Project. NASA's Goldstone Radar has also put the asteroid on its schedule, so we may yet see closeups of the object.

To create an accurate finder map for your location, head over to the Minor Planet Center's ephemeris service, type in the asteroid's name (2018 CB) in the open box and then scroll down to input your latitude and longitude. (Unsure of those numbers? Click here.) Next, select the star-mapping program from the list, click the Get Ephemerides button, and save the file into your program. Select that file when you open the program and plot your own customized path.

How Hazardous is Potentially Hazardous?

Screaming across the sky
Asteroid 2018 CC, another Earth-approacher, was captured Tuesday when it zipped just 490,000 km from Earth.
Gianluca Masi / Michael Schwartz

There's a widespread misconception that close-approaching asteroids are a danger to the planet. They are, if their path takes them on a collision course. But 2018 CB will be traveling at around 26,000 mph (58,000 km/hour). With that much speed and momentum, it can't be pulled in by Earth's gravity, so there's no cause for alarm.

All of these objects move quickly, and as close as they might come, they're soon on their way — though not without a parting gift from our planet. Earth's gravity will alter 2018 CB's orbit to some degree, so it will leave our vicinity on a somewhat different track from which it arrived.

New Earth-approachers are discovered all the time while old ones keep making the rounds. At least 10 more space rocks will be passing our way before the end of the month.

Check out this video created by Tom Ruen showing Earth as seen from asteroid 2018 CB during Friday's flyby.

The steady pace of asteroid discovery is heartening. Automated surveys have revealed that Earth-approaching asteroids are common, which means they've been flying by in great numbers long before the surveys began. The good news is that in spite of the potential threat, untoward impacts of larger objects are exceedingly rare.




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