Have you noticed a bright light appearing in the sky right after the Sun sets below the horizon, this time of the year? And have you noticed that, other times of the year, the same bright object is visible before sunrise on the opposite side of the sky? Is it a plane, a satellite, a star?
Well, actually it is none of the above, but it is one of the most interesting celestial objects and we are here to tell you all about it!
The ancient Romans called it Vesperus, the ‘evening star’, when it appeared in the western sky after sunset, and Lucifer (not THAT Lucifer! actually the word in Latin means ‘light bearer’), the ‘morning star’ when it showed in the eastern sky before sunrise: most other ancient civilisations considered those being two different stars. Turns out, not only is it the same object, but it is not a star after all. Actually, it is the second closest planet orbiting the Sun after Mercury…still wondering what it is?
The answer is: Venus!
It is called a terrestrial planet just like our Earth, Mercury and Mars to differentiate them from the two gas giants, Saturn and Jupiter, and the two ice giants, Uranus and Neptune. Some of you might ask: what about Pluto? well, unfortunately Pluto has been demoted so it is not considered an official planet of our Solar system anymore, but we will write a post on it in the near future if you are interested…
Back to Venus now. To make this entry interesting, we will highlight some facts about the planet that you may not know about so you will impress your friends on the next trivia night 😉
First, it is the third brightest celestial object after the Sun and the Moon. So it is easy to spot when you know where to look. It is sometimes possible to see it even during the day!
Although it is a rocky planet, when we look at it we are not able to see its surface because it is shrouded in a dense layer of clouds. The slightly yellow cast that we see through the telescopes during our stargazing tours is caused by these clouds. For the most part, they are made of carbon dioxide (the greenhouse gas mostly responsible for global warming on Earth at the present time) and the upper layer is composed of sulfuric acid…talk about a welcoming environment!
To be able to see the surface, we had to wait until 1975 when the Venera 9 and 10 probes from the Soviet Union were able to land on the planet and transmit the first images. Well, if you thought the cloud layer was inhospitable, the temperature on the surface reaches 460º C making it the hottest planet in the solar system! You might think that that record belongs to Mercury, the closest planet to the Sun, but because it does not have an atmosphere, temperatures fluctuate wildly but never reach those heights. In addition, the pressure on the surface of Venus is so high that it feels like having two Empire State Buildings on every inch of your body!
If all that was not enough, the planet has ongoing volcanic activity (I guess Elon Musk and his billionaire friends will not colonise it anytime soon…).
Aside from its physical characteristics, Venus is extremely interesting as regards its motion around the Sun: the average distance is 100 million km, or 72% the average distance between the Earth and the Sun, and its orbit is the closest to being circular, as opposed to all the other planets that have a more elliptical motion. What makes the planet unique in the solar system, though, is the fact that it spins on its axis in retrograde rotation (clockwise when we view the solar system from above the Earth’s north pole), and the reason could be the fact that its thick layer of clouds cause a lot of drag, thus slowing down and eventually reversing the normal counterclockwise rotation all the other planets share.
Another mind-boggling aspect of its orbit is that one Venusian day lasts longer that a Venusian year! how is that even possible? Let me explain: because of its slow retrograde motion, the planet takes 243 Earth days to complete a 360º rotation (or sidereal day), whereas it orbits around the Sun it 224.7 Earth days. But wait! if your head is not spinning already, keep in mind that there is another type of day called solar day (the time it takes a point on the planet to have the Sun back at the same position in the sky) that is much shorter than the sidereal day at 116.75 Earth days, due to this retrograde motion. Have a look at the figure to wrap your head around this madness…
Contrary to almost all the other planets in our system, Venus does not have natural satellites, only some so-called trojan asteroids, therefore no companions to share the trip around the Sun… sad but true!
Another interesting aspect is that Venus shows phases like the Moon when we observe it through our telescopes during our stargazing tours, and the reason lies in its position relative to the Earth: as a matter of fact, when it is opposite side of the Sun (a position called superior conjunction), it appears as a small ‘full’ disc because from our vantage point the Sun lights up the complete surface facing us, whereas it presents a ‘crescent’ when it passes along the near side between our planet and the Sun. Of course, when it is closest to us (so directly between our planet and the Sun, a position called inferior conjunction) we are not able to see it because the illuminated face is opposite side.
Finally, why does Venus appear sometimes as the ‘morning star’ and others as the ‘evening star’? To answer that question, you have to keep in mind that during its orbit, which is lower than ours, the planet passes the Earth every 584 days and, as it does so, it changes from being visible after sunset to showing before sunrise.
So, next time you see a very bright object along the path of the Sun before sunrise or after sunset, it is our ‘sister’ planet Venus, one of the most interesting in the Solar System!
Written by Dani
Want to see Venus for yourself? Join our stargazing tour for an unforgettable view of the ‘Evening Star’ and many more celestial wonders. Book now and experience the magic under Tenerife’s clear night skies!
