this is my first post, so don't be upset too much
Tunguska event - the largest impact event on Earth in recorded history. Studies have yielded different estimates of the superbolide's size, on the order of 60 to 190 metres (200 to 620 feet), depending on whether the body was a comet or a denser asteroid. Modern calculations that include the effect of the object's momentum estimate that the airburst had an energy range from 3 to 5 megatons of TNT.
A large explosion that occurred near the Stony Tunguska River, in Yeniseysk Governorate (now Krasnoyarsk Krai), Russia, on the morning of 30 June 1908. The explosion over the sparsely populated Eastern Siberian Taiga flattened 2,000 km2 (770 sq mi) of forest (it caused no known human casualties). The explosion is generally attributed to the mid-air disruption of a superbolide. It is classified as an impact event, even though no impact crater has been found; the object is thought to have disintegrated at an altitude of 5 to 10 kilometres (3 to 6 miles) rather than hit the surface of the Earth.
The first recorded expedition was conducted in 1927 by Leonid Kulik team following another three and an aerial survey. A stamp was issued in 1958 to commemorate the 50th anniversary of the event and Kulik efforts to explore it.
Sikhote-Alin event - an iron meteorite that disintegrated in Earth atmosphere and fell as a rain of debris on Feb 12, 1947 in Sikhote-Alin mountains (Far East Russia close to the Russian-Chinese border) near the remote village of Beitsukhe. The overall size of the debris was estimated at 70 tons with the largest weighting 1745 kilograms. After the conflict with China in 1969 Beitsukhe was renamed to Meteoritny.
A lot of people witnessed the event and between them was an artist Petr Medvedev who was in the middle of sketching the local landscape. His painting appeared on the stamp and cover commemorating 10th anniversary of the event in 1957. The stamp was already shown here, but I include it to complete the picture.
Chelyabinsk meteorite event was the biggest since Tunguska in 1908. On the morning of Feb 15, 2013 a small asteroid (around 17 meters in diameter) entered Earth atmosphere, disintegrated and exploded at around 20km above Chelyabinsk area in Russia. The explosion yield was calculated as equivalent to 200 kiloton of TNT (although some sources estimate it as 500kT). Huge amount of small debris fell over the Etkulsk district while the biggest piece (over 500 kilograms) got into the Chebarkul Lake and was extracted half a year later.
A special postmark was used to celebrate 3rd anniversary of the event. One enthusiastic postcard designer and astrophilatelist from Chelyabinsk created a series of cards to commemorate the event and that is what I have along with some other private designs.
the last is the Romanian cover, this is not really my specialty but just another meteorite event