During the recent Venus transit (June 2012), the planet appeared as a tiny black circle moving on the Sun. The black colour on the Sun is because the planet

During the Venus transit of June 2012, the planet appeared as a tiny black circle because it was positioned directly between the Earth and the Sun, creating a silhouette [1]. Although Venus has a high albedo due to its reflective sulfuric acid clouds [2], it appears black against the solar disk because it is an opaque object that obstructs the intense light from the Sun behind it [3]. While it only blocks approximately 0.1% of the total solar light, the contrast between the extremely bright solar photosphere and the unlit side of the planet facing Earth makes Venus appear as a dark, distinct spot [1]. This phenomenon is a simple geometric effect where the planet's body prevents the light from that specific portion of the Sun's surface from reaching the observer's eye or telescope [1].

Sources

1. [1] Science-Class VII . NCERT(Revised ed 2025) > Chapter 12: Earth, Moon, and the Sun > Activity 12.4: Let us explore > p. 180
2. [2] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 2: The Solar System > Venus > p. 27
3. [3] https://www.nationalgeographic.com/science/article/120605-venus-transit-2012-sun-science-how-when