Near-Earth Objects.

Near-Earth Objects, including asteroids and comets, regularly zip past the Earth, as they roam the darkness of space. While collision with our planet is a risk, their study also reveals the secrets of life. Brace for impact!

                                 Earth Encounters

Close Approach

If an NEO is near the part of its orbit closest to Earth's, at the same time the Earth is at the part of its orbit closest to the NEO's, the object has a close approach, or, if the orbits intersect, it could even impact the Earth or its atmosphere. The first NEO known to have passed the Earth closer than the distance of the Moon was 1991 BA, which passed at a distance of 170,000 km.

Impact Event

When an NEO impacts Earth, objects up to a few tens of metres across ordinarily explode in the upper atmosphere, with most or all of the solids vapourising and only small meteorites arriving on Earth's surface (forming impact craters) while larger objects hit the water surface (forming tsunamis). The Tunguska event was a meteor air burst; the atmospheric explosion  of a stony asteroid about 50-60 metres wide that occurred near the Podkamennaya Tunguska River in Russia in the morning of 30 Jun 1908.

The explosion over the sparsely populated East Siberian taiga flattened 80 million trees over an area of 2,150 sq km of forest, killing three people.

Earth-Grazers

Some asteroids briefly enter the upper atmosphere of the Earth during their close approach, burning their surface. During this time, such an object can be observed as an Earth-grazing fireball. On 10 Aug 1972, a meteor. the 1972 Great Daylight Fireball, moved north over the Rocky Mountains from the US, south west to Canada. It passed within 58 km of the Earth's surface.

Tailpiece.

Got up at my usual time, the chores and was ready by a half past 9. Had carried out the Wednesday aa'rathi earlier.

Lekha had gone to the ration shop to collect our monthly dues.

Kittu comes in post-lunch.

A quiet evening.