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رقم العضوية : 1623  تاريخ التسجيل :  05 2002  أخر زيارة : 18-10-2003 (04:24 AM)  المشاركات : 1,327 [ + ]  التقييم :  10

لوني المفضل : Cadetblue

اختـــي الغاليـــة .. واهمــة ..


ذكرت بالشهـــــادة ياأخيتي .. و والله انا لغافلــون الى اجل غير مسمى ..

جزاك الله خيراً على هذه الكلمــات ....

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بخصوص تســاؤلك غاليتي عن مارأته صديقتك ... فلقد وجدت موقعاً

يفيدك في ذلك .. ولكني لم اتمكن من وضعه هنا .. ولهذا سأضع لك مايجيب

على تساؤلاتك ... (( والله يعينك )) ... :)

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The Close Call that was Asteroid 2002 Mbr />
The following selections are from the June 24, 2002 edition of NEO News, written & compiled by Dr. David Morrison.

2002 MN & Hazard Review
by David Morrison

On June 17, the LINEAR Spaceguard system discovered Near Earth Asteroid (NEA) 2002 MN, which had passed the Earth on June 15 at a distance of only 210,000 km, one of the closest asteroid flybys on record. Based on its brightness, 2002 MN has a nominal diameter of about 100 m, large enough to penetrate through the atmosphere to the surface if it struck the Earth.

Considerable press interest in this object has been evident, as well it might be. It has been nearly a decade since a known asteroid passed this close. Unfortunay, however, some of the press coverage has been sensationalistic. Some either de that the object was found after closest approach (rather than before) or express concern about the "blind spot" otherwise commonly known to astronomers as the daytime sky. It is quite true that an asteroid close to the Sun in the sky cannot be seen. However, if an NEA is approaching Earth from the daytime sky, it is likely to pass into the night sky, where it can be discovered, as this one was. Far from being a cause of concern, the discovery of NEA 2002 MN was another example of the success of the Spaceguard effort in general, and of the LINEAR program in particular. Similar concerns were expressed following the discovery of 2002 EM7 two months ago, but there is no cause for "doom and gloom" in either of these asteroids.

Presumably a part of the problem is that many people do not understand the Spaceguard Survey strategy to discover and catalog NEAs long in advance of any possible threat, providing decades (or more) of warning if any is currently on a collision course. Both of these asteroids were successfully found, although they are well below the 1-km diameter that is emphasized by the current Spaceguard effort. It makes no difference if a NEA is discovered on approach or departure from the vicinity of the Earth. We don't give extra points for an approaching NEA or demerits for one that has already passed the Earth at discovery. The only effect of "blind spots", whether they be due to sunlight or moonlight or bad weather or lack of a southern hemisphere survey escope, is to slow down the completion of the NEA catalog. Objects in blind spots will be missed until they move into a more favorable geometry, sometimes within a few days, otherwise usually within a few years.

To put this latest asteroid in perspective, a 100-m asteroid hits the Earth at an average interval of a few millennia. One passes within the orbit of the Moon, however, several times per year. This has been happening throughout history. What is new is that we are now beginning to discover these objects, whereas previously they would have sped past undetected and unheralded.

Following are some press comments on 2002 MN. I believe that we are making progress, in that many of the news reports on 2002 MN do accuray reflect the situation as the astronomers understand it.

For a comprehensive review paper on the asteroid impact hazard now in press for the book Asteroids III, visit the NASA impact hazard website at www.impact.arc.nasa.gov. Of particular interest to some will be a revised estimate of the frequency of impacts of NEAs as a function of size.

- David Morrison.

Near Earth Object Information Centre
National Space Centre, Exploration Drive, Leicester
Press Release, Thursday 20th June 2002: Asteroid 2002Mbr />
Asteroid 2002MN gives Earth its closest shave in years

On Friday 14 June, an asteroid the size of a football pitch made one of the closest ever recorded approaches to Earth. Astronomers working on the LINEAR search programme, near Socorro, New Mexico first detected the giant rock on 17 June, a few days after its close approach.

The Near Earth Object, known to astronomers as '2002MN', was travelling at over 10 km/s (23,000 miles per hour) when it passed Earth at a distance of around 120,000 km (75,000 miles), bringing it well inside the Moon's orbit. The last time a known asteroid passed this close was back in December 1994.

Asteroids are typically too small and distant to measure their size directly from Earth, so scientists use the amount of light they reflect, along with a basic understanding of the materials they are made of, to estimate their size. With a diameter between 50-120 metres, 2002 MN is a lightweight among asteroids and incapable of causing damage on a global scale, such as the object associated with the extinction of the dinosaurs.

However, if it had hit the Earth, 2002MN may have caused local devastation similar to that which occurred in Tunguska, Siberia in 1908, when 2000 square kilometres of forest were flattened. Whilst the vast majority of NEOs discovered do not come this close, such near misses do highlight the importance of detecting these objects. This reminder comes in a week when the UK escopes on La Palma are being tested to search for NEOs.

Brief De??????ion of Object

Object Designation: 2002MN

Date of First Observation: June 17, 2002

Number of Observations: 14

Search Team: LINEAR (Lincoln Near Earth Asteroid Research)

Date of Closest Approach: June 14, 2002

Closest Approach Distance: 119,229 km (0.3 Lunar Distances)

Asteroids Velocity Relative to Earth at Closest Approach: 10.58 km/s

Estimated Diameter of Asteroid: 50-120 metres

Orbital Period: 894.9 days







آسفــــــة على الإطالة .... ولكن انت من أراد المعرفة .. :D :p ;)
ولا تنكري انه شيق .....!!!! فهذه الامور تستهوي مثايـــــــل ...:D


لك تحيــــاتي ...

مثايــــــل الخيـــر