People in Tehran and other towns across Iran observed the rare phenomena of transit of Venus across Sun on Wednesday morning.

A transit of Venus across the Sun takes place when the planet Venus passes directly between the Sun and Earth, becoming visible against the solar disk. During a transit, Venus can be seen from Earth as a small black disk moving across the face of the Sun.
A transit is similar to a solar eclipse by the Moon. While the diameter of Venus is more than 3 times that of the Moon, Venus appears smaller, and travels more slowly across the face of the Sun, because it is much farther away from Earth. The transit of 2012 lasted 6 hours and 40 minutes.

Transits of Venus are among the rarest of predictable astronomical phenomena. They occur in a pattern that repeats every 243 years, with pairs of transits eight years apart separated by long gaps of 121.5 years and 105.5 years. The periodicity is a reflection of the fact that the orbital periods of Earth and Venus are close to 8:13 and 243:395 commensurabilities. (read more on wikipedia)
Photos by Fatemeh Behboudi & Hossein Esmaeili, Mehr News Agency