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8 July 2010 Asteroid Roma to pass in front of Delta Ophiuchi - Visible to naked eye

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posted on Jul, 6 2010 @ 07:42 AM

In a rare event on July 8, 2010, skywatchers will be able to see an asteroid briefly block out the light from a star as it passes in front. It may be the only asteroid 'occultation' this century observable with the naked eye.

Everybody 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. In total, we know of about 400,000 of these dark bodies, which range in size from a few hundred kilometres to just a few metres.

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 many stars in the night sky and block its light from our view, causing a stellar eclipse or occultation. Since asteroids move relatively fast, these events typically last just a few seconds. Normally the occulted star is so faint the event can only be seen via telescope.

During the night of 8/9 July, a star that is visible to the naked eye, Delta Ophiuchi (the fourth-brightest star in the constellation Ophiuchi), will be occulted by asteroid Roma, which has a diameter of about 50 km. This means the occultation will be visible only along a path about 50 km wide, crossing central Europe, Spain and the Canary Islands.

Catching a glimpse

Since asteroids, with very few exceptions, 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.


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