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Once-in-a-lifetime eclipse by asteroid to treat Europe
July 5, 2010
Courtesy of the European Space Agency
and World Science staff
In a rare event next Thursday, some skywatchers in Europe will be able to
see a star briefly vanish as an asteroid passes between it and
us. Astronomers say the event may be the only eclipse of a star by an asteroid this century
visible with the unaided eye. Star chart showing the sky from central Europe, facing south just
before midnight on July 8. The star Delta Ophiuchi will be about half-way
between the horizon and the zenith or "top" of the sky.
(Credits: ESA, created with Guide 8 by Project Pluto, http: Send us a comment
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it to a friend Homepage image: ESA's Optical Ground Station in Tenerife,
Spain is used for asteroid observations. (Courtesy ESA)
Everyone is familiar with a solar eclipse, when our Moon passes in front of the Sun and blocks its light for several minutes.
A similar situation can happen with asteroids, the Sun-orbiting, rocky or metallic objects left over from the formation of the Solar System or formed by
crashes between other asteroids.
We know of about 400,000 of these dark bodies, which range in size from a few hundred kilometres (miles) to just a few metres (yards).
Smaller ones are hard to detect.
While an asteroid is far too small to cover the Sun, one will occasionally move directly in front of one of the stars in the night sky and block its light from us, causing a stellar eclipse or occultation. Since asteroids move fast, these events typically last just a few seconds.
Normally the occulted star is so faint the event can only be seen via telescope. But the night of 8-9 July, a star visible to the naked eye, Delta Ophiuchi (the fourth-brightest star in the constellation Ophiuchi), will be occulted by asteroid Roma, about 50 km (30 miles) wide.
This means the eclipse will be visible only along a path of about that same width, crossing central Europe, Spain and the Canary Islands. At about 11:57 p.m. Central European Summer Time, observers on a line running between Stockholm -
Copenhagen - Bremen - Nantes - Bilbao will see the star disappear for about five seconds as its light is blocked by the asteroid.
Since most asteroids are too small to be resolved with ground-based telescopes, asteroid occultations are the only direct way of measuring the size of such an object. When several observers record such an event, using videocameras with precise timing, the times when they see the occultation help to measure the shape of the asteroid.
Since we know the speed of the asteroid, the duration of the occultation can be converted directly to a length. This allows scientists to reconstruct the size and shape of the object.
Asteroids coming close to Earth are the focus of a new European Space Agency monitoring program, known as the Near Earth Object segment of the Space Situational Awareness Preparator Programme.
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In a rare event next Thursday, some skywatchers in Europe will be able to see an asteroid briefly block out the light from a star as it passes in front. Astronomers say the event may be the only eclipse of a star by an asteroid this century observable with the naked eye. Everyone is familiar with a solar eclipse, when our Moon passes in front of the Sun and blocks its light for several minutes. A similar situation can happen with asteroids, the Sun-orbiting, rocky or metallic objects that are left over from the formation of the Solar System or were formed by collisions between other asteroids. We know of about 400,000 of these dark bodies, which range in size from a few hundred kilometres (miles) to just a few metres (yards). The smaller ones are hard to detect. While an asteroid is far too small to cover the Sun, one will occasionally move directly in front of one of the stars in the night sky and block its light from us, causing a stellar eclipse or occultation. Since asteroids move fast, these events typically last just a few seconds. Normally the occulted star is so faint the event can only be seen via telescope. But the night of 8-9 July, a star visible to the naked eye, Delta Ophiuchi (the fourth-brightest star in the constellation Ophiuchi), will be occulted by asteroid Roma, about 50 km (30 miles) wide. This means the eclipse will be visible only along a path of about that same width, crossing central Europe, Spain and the Canary Islands. At about 11:57 p.m. Central European Summer Time, observers on a line running between Stockholm—Copenhagen—Bremen—Nantes—Bilbao will see the star disappear for about five seconds as its light is blocked by the asteroid. Since most asteroids are too small to be resolved with ground-based telescopes, asteroid occultations are the only direct way of measuring the size of such an object. When several observers record such an event, using video cameras with precise timing, the times when they see the occultation help to measure the shape of the asteroid. Since we know the speed of the asteroid, the duration of the occultation can be converted directly to a length. This allows scientists to reconstruct the size and shape of the object. Asteroids coming close to Earth are the focus of a new European Space Agency monitoring program, known as the Near Earth Object segment of the Space Situational Awareness Preparatory Programme.