If you are up before dawn and the sky is clear, you will see a brilliant star in the east. This is the ‘Morning Star’. Actually, it is not a star (a star is a Sun), it is the planet Venus.
Venus is the brightest star-like object in the sky. At maximum brightness, if you know where to look, it can be seen in broad daylight. For Polynesian sailors, it was an important navigational beacon because, due to its brilliance, it could be seen in the twilight, when no other stars were visible.
Because Venus is closer to the Sun than the Earth, in any one year it is either in the early morning or the early evening sky. Hence the popular names Morning Star and Evening Star. In ancient times, the two manifestations were thought to be different planets, Hesperus and Phosphorus. However, both the morning and evening stars were traditionally associated with the goddess of love and sex, known as Aphrodite (Greece), Ishtar (Babylon), Astarte (Syria) and Venus (Rome).
In size Venus is very similar to Earth. Its mass is 0.815 that of the Earth, and its diameter 12,104km. However, its surface is perpetually shrouded in cloud so that its topography was unknown until the space-age. It was originally believed to be a primordial world similar to the Earth millions of years ago. When I was a kid it was even suggested that dinosaurs may dwell there.
Like the Earth, Venus has mountains, valleys, and volcanoes. The highest mountain, Maxwell Montes, is 8.8km high, similar to Mount Everest. But there the resemblance ends. Its environment is the nearest thing to hell that you could imagine.
We now know that Venus was once a planet like the Earth with oceans of liquid water. Over billions of years the Sun’s increasing brightness generated a runaway greenhouse effect. The Venusian oceans boiled away leaving a thick atmosphere of carbon dioxide with clouds of sulphuric acid. The surface temperature is 470oC, hot enough to melt tin and lead. And, at the surface, the atmospheric pressure is as high as 90 atmospheres.
Because the Sun continues to slowly brighten, the same fate awaits the Earth. Fortunately, this shouldn’t happen for billions of years. Unless, that is, we continue to accelerate global warming by polluting the atmosphere with greenhouse gases.
Richard Hall
Stonehenge Aotearoa
Photo credit – NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington