Venus is the planet most like Earth in terms of size, and it's the one that approaches closest to Earth. It's also the planet that is easiest to find in the night sky – or more correctly, the dusk or dawn sky.
Venus is never farther than 48 degrees from the sun and is visible for a little less than three hours after sunset or before dawn. That's why it has been known throughout the ages as the morning star and evening star. It may not be an actual star, but it's the third brightest object up there.
Venus in the Sky
It's almost midnight, you're on a camping trip and you start searching the sky for planets, satellites, shooting stars and UFOs. If they are above the horizon, you should be able to identify Mars, Jupiter, Saturn and – if you have good eyes – Uranus, but no matter how much you look, you won't find Venus, even if there's no moon and the sky is completely clear. That's because it's night, and Venus is accompanying the sun on the opposite side of the planet at the moment.
Like a necklace or bracelet, Venus is more or less permanently connected to the sun, and you'll always find it near the horizon – never in the mid-heaven. It doesn't rise any higher than 46 degrees when it's visible. It does, of course, cross the mid-heaven, just like every other planet, but that occurs during the day, when it's outshone by the sun. Whether you see Venus just after sunset as the evening star or just before sunrise as the morning star depends on where Venus is in its orbit.
Also, depending on its orbit, Venus may not be visible at all. When it's closer to the sun than about 5 degrees, the sun's glare completely obscures it, even at sunrise and sunset. However, when its orbit reaches maximum elongation as seen from Earth, Venus is the third brightest object in the sky, after the sun and moon. It can be a startling sight, and it accounts for a significant number of UFO reports.
Will Venus Be Visible Tonight?
Venus completes an orbit every 224 days. If it appears at sunrise as the morning star, it will remain that way for a few months until its orbit brings it between the Earth and sun or behind the sun and it disappears. It reappears about a year later at sunset as the evening star and remains visible for a few months more. The time between its first appearance as the morning star and its first appearance as the evening star – and vice versa – is about 1.6 years.
If you're wondering whether you'll be able to see Venus tonight, you can consult tonight's sky chart. It will tell you the angular separation between Venus and the sun, and if the separation is more than 5 degrees, Venus should be visible. If the separation is not much more than 5 degrees, don't expect to see Venus very high in the sky or for very long. Also, depending on which side of the sun the chart tells you Venus is currently positioned, you may be able to see Venus in the west at night or you may have to wait until morning and look to the east.
By the way, one of the most effective approaches if you're looking for a "chart of the night sky tonight from my location" is to use a mobile phone app. Sky Guide and other apps like it use the phone's navigation hardware to provide a real-time picture of the sky at any time of day.
Simply open the app, point the phone at the sun and move it slightly along the dotted line that marks the ecliptic until you find Venus. This is the fastest way to gauge the angular separation. You can also tell whether Venus is leading the sun or trailing it, which tells you whether to look for the planet at sunrise or sunset.
When Is Venus at Its Brightest?
The brightness of the Venus, as seen from Earth, depends on two factors. One is the phase, or the percentage of its face that is illuminated by the sun, and the other is its distance from Earth.
Paradoxically, Venus does not appear brightest when its face is completely illuminated, because that occurs when its orbit brings it behind the sun and farthest from Earth. Venus is closest to Earth when it's in its crescent phase, and it appears brightest when less than half of its face is illuminated.
When it appears in the west as the evening star, it reaches its maximum brightness a few days after its maximum elongation from the sun. It's also at its brightest a few days before it reaches maximum elongation when it appears in the east as the morning star.
Why Is Venus So Bright?
A planet's ability to reflect light and shine like a gem in the sky is called albedo, and Venus has it in spades. Technically, albedo is defined as the ratio of reflected light to incident light, so the higher the albedo, the more reflective the object.
Throughout the solar system, most planets score around 0.30, which is the number assigned to Earth's albedo. Some, like Mercury and Mars, are lower, but Venus has an albedo of 0.75, which is more than double that of any other planet.
The dramatic brightness may evoke images of the goddess of beauty on Earth, but it's caused by conditions that more resemble Hades than Heaven. Venus has a thick cloud cover, and the clouds don't contain any life-giving gases, such as oxygen or water vapor. They contain contain a mixture of carbon dioxide and sulphuric acid, and they are so dense that the atmospheric pressure at the surface is about 90 times what it is on Earth.
At 870 degrees F (465 degrees C), the surface temperature is hot enough to melt lead. No human could survive there, and even mechanical probes don't last long. None of the Soviet Venera probes that reached the surface in the 20th century lasted longer than an hour.
Exploration of Venus
With boiling temperatures and sulfuric acid rain, it's an understatement to say that the weather isn't very good on Venus. Has NASA ever landed on Venus?
The answer is no, but the agency has sent exploratory probes. Mariner 2 flew within 34,000 kilometers of the planet in 1962, and Pioneer Venus orbited the planet in 1978 to study, among other things, its solar wind. Magellan, launched in 1989, orbited the planet and mapped 98 percent of the surface by radar.
Up until now, the U.S. agency has preferred to study the data supplied by Soviet probes rather than sacrifice its own. For their part, the Russians have announced no plans to send another probe to Venus, but that doesn't mean they won't. Other space agencies have sent probes to Venus, however. The European Space Agency launched Venus Express in 2006. It orbited the planet for eight years, studying, among other things, how Venus lost its water. Spoiler alert: There's a good chance the solar wind did it.
The Japanese Aerospace Exploration Agency (JAXA) sent the most recent probe in 2010. The Akatsuki spacecraft encountered problems on its journey, however, and had to spend five years orbiting the sun before it successfully dropped into orbit around Venus on Dec. 6, 2015. It continues to send back data about topography and climate.
Venus and Global Warming
The extreme build-up of carbon dioxide in Venus' atmosphere is largely responsible for the hellish conditions on the planet. There's a natural tendency for Earth dwellers to take that as a warning, given the rapid increase of carbon dioxide in our own atmosphere.
The warning is worth heeding, but it's important to remember that Venus and Earth are two very different places. The data we have received from probes such as Magellan, Venus Express and Akatsuki confirm this.
The surface of Venus, unlike that of Earth, is ridden with volcanoes. Many are still active and spew gases into the already poisonous atmosphere. The surface is dry. Sulfuric acid rain does occur in the upper atmosphere, but it evaporates before it hit the ground. Water exists only in trace amounts. It's possible it simply boiled away into space, but the ESA discovered another mechanism that may account for the complete lack of water on a planet that scientists believe used to have as much water as Earth.
The Venus Express probe discovered that hydrogen gas is continuously stripped from the day side of the planet and radiated into the space on the night side. This effect is caused by the solar wind, which is much stronger on Venus that it is on Earth due to Venus's proximity to the sun. Together, rising temperatures caused by CO2 buildup and the effects of the solar wind could have turned Venus into the inferno it is today. It's unlikely the same thing would happen in the exact same way on Earth.
A Holiday on Venus
You probably wouldn't want to spend any length of time on Venus, but if you somehow found the proper survival equipment and caught the next probe, you'd find things very different than they are on Earth.
Venus spins in the opposite direction from all the other planets, so the sun would rise in the west and set in the east. Moreover, it spins so slowly that a day, which lasts 243 Earth days, is longer than a year, which takes 224 Earth days. In any given year, you would see a sunrise or a sunset, but not both.
From your encampment, which, like a deep-sea probe, would have to be pressurized to withstand the force of the atmosphere, you would see a semi-molten terrain stretching out in all directions. It's mostly flat, but it's punctuated by volcanoes and lava flows that have carved out canals, some of which are thousands of miles long.
Venus does have mountain ranges, and if you're near one of them, you might be able to see peaks that reach elevations of as much as 7 miles.
Besides all this, you'd see features that are completely alien to Earth dwellers. The molten material underneath Venus' crust rises up to form large ring-like structures called crowns. They can be 95 to 360 miles (155 to 580 km) wide.
Volcanic activity is also responsible for raised areas on the surface called tiles, which have ridges that splay out in multiple directions. After taking in this scenery, you'd probably be happy to cut your holiday short and return to Earth, where you can appreciate Venus as a gem in the night sky rather than the hostile place it actually is.