Of the seven other planets in our solar system, none parallels the beauty of Venus as seen from Earth with the unaided eye. The second planet from the sun is currently rapidly approaching Earth, with the two planets eventually reaching a minimum distance of 43 million kilometres in early June. In our current evening skies, Venus appears as an extremely bright ‘star’ towards the west. In a few months, however, it will instead be visible as a very bright star in the early morning sky instead.
Indeed, Venus has been known since ancient times as both the morning star and the evening star, at first believed to be two separate cosmic objects. When Venus is approaching the Earth in its orbit around the sun, it is observed from Earth in the evening sky. Conversely, when it ‘overlaps’ the Earth in its orbit, and is thus moving away from Earth instead, Venus is seen in the morning sky. This occurs because Venus is closer to the sun than Earth. Apart from one Venusian orbit actually being physically smaller than Earth’s orbit, Venus also travels around the sun faster than Earth. This results in one Venusian year lasting around 225 Earth days, as opposed to Earth’s year lasting approximately 365.25 days.
Being closer to the sun than Earth, Venus exhibits phases when observed through a telescope. As Venus gets closer, it appears larger in a telescope but less and less of the sun-facing side of the planet can be seen from Earth, since the angle between Venus and the sun in the sky gets smaller. This effectively means that the closer Venus gets, the thinner the crescent of the planet we observe from Earth. However, the crescent itself gets larger in apparent diameter – an observation which Galileo made for the first time with his telescope in 1610.
Although Venus gets closer to Earth than any other planet, surface details on Venus are impossible to see in visible light as a result of the thick clouds shrouding the surface of Venus from view. The Venusian atmosphere is, in fact, extremely thick, with surface pressure around 90 times that on Earth. Indeed, Venus can be observed through a telescope as featureless and white.
Being mostly made of carbon dioxide, Venus’s atmosphere has resulted in a runaway greenhouse effect on the planet, with surface temperatures reaching a scorching 450ºC. This makes Venus hotter at the surface than Mercury, even though Mercury is much closer to the sun.
Josef Borg is currently a PhD student at the Institute of Space Sciences and Astronomy, University of Malta, and also the president of the Astronomical Society of Malta.
Sound bites
• Newfound black hole is the closest ever found to Earth: A newly-found black hole could be the closest black hole to Earth. The black hole, which can be found around 1,000 light-years from Earth, forms part of a system including two companion stars, observable with the naked eye, even though the black hole itself cannot be observed.
https://www.space.com/closest-black-hole-to-earth-discovery.html
• Comet SWAN is expected to appear in northern skies in late May: Comet SWAN (C/2020 F8) has given us fresh hope of a bright comet in 2020. Southern hemisphere observers have the best views of the comet in early May, but that will change as the comet moves northward.
https://skyandtelescope.org/astronomy-news/comet-swan-expected-to-put-on-a-splendid-show/
For more soundbites listen to Radio Mocha every Saturday at 7.30pm on Radju Malta and the following Monday at 9pm on Radju Malta 2 https://www.fb.com/RadioMochaMalta/
Did you know?
• Polar ice caps and other surface features on Mars are normally visible through medium sized telescopes. Notwithstanding Mars’s small size, the red planet gets close enough to Earth at opposition that small features on its surface become easily distinguishable with a telescope. However, Mars is sometimes engulfed by global dust storms, rendering views of the surface unclear.
• Jupiter can be seen making one full rotation in one night on particular long nights. If Jupiter is near opposition, when nights from the observing location last at least 10 hours, it is possible to view one entire rotation of the Jovian giant in one night. Jupiter completes one rotation on its own axis in just nine hours and 55 minutes.
For more trivia, see: www.um.edu.mt/think