A remarkable event will be observed in the skies above Bulgaria early morning on Wednesday June 6, when Venus will pass across the face of the sun — a phenomenon known as a transit.

The transit won't happen again until 2117. The rare event is anticipated with huge interest from scientists while travel agencies are offering trips to Alaska where the entire transit will be visible.

The second planet in the solar system will cross the line between the Earth and the Sun and will appear as a small, black dot on the backdrop of the sun's disc.

Transits of Venus are so rare because the planet's orbit is tilted relative to the Earth's. The phenomenon has been first observed in the 17th century. The two planets line up with the sun only four times every 243 years. (The timing between transits is: 121.5 years, then eight years, then 105.5 years, then eight years again.) The first transit for the 21st century happened in 2004.

Bulgaria's National Astronomical Observatory announces that in Bulgaria the transit can be seen from the moment of the sunrise on June 6 – at 5:29 am in the Black Sea city of Varna and at 5:49 am in the capital Sofia.