Hi I’m Alex McColgan, and you’re watching
Astrum. Now today we are going to be looking at the
beautiful yet hellish planet of Venus. We’re going to be delving into what makes
this planet so unique in our solar system, so get ready to find out everything you could
want to know about Venus. Visually, it is a very beautiful and elegant
planet. Seemingly very calm and almost tranquil on the surface. From an outsider’s perspective, it’s clear
why it’s named after Venus, the Roman god of Love. Go beneath the cloud layer, and you’ll
find quite the opposite. Scorching temperatures, volcanism and a crushing
atmosphere are what you'd actually find on the surface. But let’s step back a bit and see where
this planet fits in our solar system. Venus is the 2nd planet from the Sun and is
our closest neighbour. Its average orbital radius around the Sun
is 0.72AU or roughly 108 million kms. It doesn’t vary much at all from this mean
orbital radius, as it’s the planet with the least eccentric orbit, orbiting nearly
in a perfect circle. At Venus’ closest approach to us, it is
the closest of any other planet, being only 41 million kms away. Interestingly though, this is not when it’s
brightest in our sky, as when its closest to us, we only see the night side as it’s
between us and the Sun. It is still visible though as the sunlight
refracts through the atmosphere. It’s actually brightest when it’s a thinner
crescent shape in the sky, and when this happens, it is the brightest object in the night sky
after the moon. As such, Venus is a commonly misreported "unidentified flying object". U.S. President Jimmy Carter reported having
seen a UFO in 1969, which later analysis suggested was probably Venus. Countless other people have mistaken Venus
for something more exotic due to its startling brightness. I recently had the pleasure of looking at
Venus through a telescope and remarkably the crescent shape of it was very visible. With Venus orbiting between us and the Sun, it may make you wonder if Venus ever eclipses the Sun from our viewpoint on Earth, and the
answer is yes, but surprisingly, very rarely. Transits happen in pairs, the pairs being
8 years apart, but every pair only happens once every 100 or so years. The last transit we had was in 2012, but if
you didn’t see that I’m afraid the next one won’t be until 2117. The reason for this rarity is because the
orbiting plane of Venus is not exactly the same as Earth’s. Also, Venus only catches up with Earth every
584 or so days. These two things combined ensure that although
a spectacular and predictable sight, it also means we’ll probably only ever have the
chance to see it twice in our lifetimes. All the planets orbit anticlockwise around
the Sun and with this, Venus is no different. But unlike all the other planets it rotates
clockwise, or in other words in a retrograde rotation. Not only that, but it has an extremely slow
rotation, rotating once every 243 Earth days – slower than any other planet. This makes a sidereal day longer than a Venusian
year, a Venusian year lasting 224 Earth days. A sidereal day, if you remember from the Mercury
episode, is one rotation of the planet. Because of this retrograde rotation though,
a solar day (which is sunrise to sunrise) is considerably shorter, at 117 Earth days. This means you’d only experience just less
than 2 days on Venus in one year. To give some perspective as to how slowly
it rotates, at the equator the planet is only rotating at 6.5km/h! This slow rotation makes it the second most
spherical object in the solar system, after the Sun. It is unclear why Venus rotates backwards
compared to the rest of the planets, but it could be due to a big impact with another
object billions of years ago, or tidal locking with the Sun, or tidal effects on the Venusian
atmosphere. Its mass and size are very similar to our
Earth, hence why it’s often referred to as our sister or twin planet. Venus is one of the four inner terrestrial
planets and it is a rocky planet. Its diameter is slightly smaller than Earth’s
at 12100km compared to 12740km and its density is 5.243 g/cm3 compared to our 5.514 g/cm3. This means the gravity on Venus is only a
tenth weaker than on Earth, surface gravity being 8.87 m/s2, or 0.9g. But this is where the similarities end. On the surface of Venus, the atmosphere’s
pressure is 92 times greater than on Earth’s. That’s an equivalent of 1km under Earth’s
oceans. The reason for this is because the density
of Venus’ atmosphere is 93 times greater than Earth’s. And fit that amount of gas into a space slightly
smaller than what we have here on Earth, and you can understand why it’s so densely packed. The atmosphere consists mainly of CO2 gas,
and combined with sulphur dioxide clouds, you’re left with the strongest greenhouse
effect in the solar system, with temperatures 462c at the surface on average. This makes the surface temperature greater
than Mercury’s, even though Mercury is the closest planet to the sun and Venus only gets
25% of the solar radiation Mercury does. The difference is that Mercury doesn’t have
an atmosphere to retain the heat, whereas Venus certainly does. This means at night time and even at the poles,
the temperature remains fairly constant. Venus really is cooking, it absorbs so much
heat but like a thermal flask it retains it and doesn’t let much escape. With an axial tilt of only 3 degrees, it also
means seasonal changes in temperature are also very minimal. Wind speeds aren’t very high on Venus’s
surface, only being a couple of kilometres an hour, but because of the thickness of the
atmosphere it applies a very strong force on obstructions, moving small rocks and dust
across the surface. On the other hand, wind speed at the cloud
layer is much faster, reaching speeds of 300km/h. These winds at the cloud tops circle the planet
about every four to five Earth days which makes the planet look like its rotating a
lot faster than it actually is. The cloud layer itself sits above the thick
CO2 and consists mainly of sulphur dioxide and sulphuric acid droplets. Sulphuric acid, just as a side note, is highly
corrosive and this acid rain just adds to the hellish nature of Venus, although it does
evaporate before it hits the surface. The clouds on Venus are highly reflective,
only allowing about 10% of the sunlight through, and because they cover the entire planet,
it obstructs a visual view of the surface from space. These clouds are also capable of producing
lightning much like on Earth, although not as common. Recently it has been discovered that Venus
has a large vortex at the South Pole much like on Saturn. Venus is the image on the left, and Saturn
on the right. They are shaped quite differently, and Venus
only has the one storm, whereas incredibly every single black dot in the Saturn image
is a separate storm, with the main vortex in the centre. The vortex on Venus is at an altitude of 59km
which is just above the cloud deck. Which leads on to an interesting point about
the atmosphere of Venus. At about 50km up, the air pressure and temperature
are tolerable for Earth standards. Even the gravity would feel very much like
Earth. The only problem with a person being there
is the air itself. But if you were to have an airtight plane
or something, conditions would be very Earth like. I want to head back down to the surface of
Venus a little bit, as we actually have real photos of the surface thanks to the pioneering
efforts of the Russians back in the 60s to 80s. The probe Venera 7 in 1970 was the first probe
to ever land on another planet and send back data, the previous attempts resulted in the
probes signal terminating before touchdown. Venera 7 probably fell over on impact though,
and so the only reading it gave was the temperature at the surface of 475 degrees. Venera 8 confirmed that at the surface the
visibility was quite clear, with about a km range, as the cloud layers end at quite a
high altitude meaning it was suitable for cameras in future missions. Venera 9 sent back the first ever image of
the surface of Venus. Venera 10, 13 and 14 over the course of 6
years sent back more imagery, this time in colour, as well as a lot of data regarding
the conditions of the planet. Since then, there have been a number of probes
that have mapped out the surface of Venus. Using radar, they were able to see through
the cloud cover and see the planet’s landscape in very high definition. The surface of Venus is dotted with a lot
of big, but not necessarily active volcanos. It has 167 volcanos which are over 100km in
diameter. The only complex this size on Earth is the
big island of Hawaii. This doesn’t mean Venus is more volcanically
active than Earth, but this is due to the fact that Venus has a much older crust than
Earth. Earth has plate tectonics releasing heat and
renewing the surface fairly regularly, (regularly being 100 million years) but Venus doesn't have any plate tectonics. Instead its crust is estimated to be about
300-600 million years old, when a global resurfacing event likely occurred. The theory is that the mantel under the crust
heated up so much that it forced its way through the crust, covering most of the surface with
lava. An incredible 80% of Venus' surface is made
up of cooled lava plains, and there are literally hundreds of thousands of volcanos in one form
or another. There are 900 impact craters also to be found
on Venus, although none less than 3 km in diameter. This is because anything smaller than 50m
in diameter would fragment and burn up before it even hit the surface. And finally let’s have a look at the magnetosphere. Venus doesn’t have its own magnetic field,
which surprised everyone when it was first discovered as Venus’ composition is similar
to Earth’s. But without more data, it’s hard to say
why this might be. As a result of this, solar and cosmic radiation
interacts a lot with the upper atmosphere of the planet, producing lightning and an
induced magnetosphere. Solar wind also strips off the low density
molecules out of the upper atmosphere meaning that Venus has a tail, similar to a comet. Under certain conditions, this tail can tickle
Earth when they in conjunction with each other. Unfortunately this tail isn’t visible with
the naked eye. Sadly, we''ve come to the end of the video. But I'd just like to say thank you so much for watching this far. And if you enjoyed it, I have a lot of other videos about our other planets which may be of interest to you as well. So be sure to check those out! And if you find space generally interesting, please subscribe! As this channel is dedicate just to that. Thanks again for watching and see you next time.
That was great!! Very informative... Now I want to know all about Uranus.