# How can we see Venus at night?

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According to the Globe Earth Theory, the Sun is in the middle of the Solar System and the Earth is the 3rd planet from the Sun, making Mercury and Venus between Earth and the Sun. If this is true, Mercury and Venus should only be seen from the lit side of the planet, since it is always between the Sun and Earth. How can you see it at night?

We can see Venus at night (dusk) and in the morning (predawn), just not all night or every night.

We need some geometry to understand this, and it boils down to tangents.

I've shamelessly borrowed this diagram from a paper to show the idea. It's discussing Mercury, but it's the same idea for Venus.

We'll simplify things by using the pretty good approximation that Earth and Venus have circular orbits. We'll also assume Earth is a perfect sphere - another good approximation. We're also assuming Earth's rotation is not at an angle to the plane of it's orbit (that's the worse approximation !). Finally we're going to assume the orbits are not inclined (not a bad approximation, but not strictly true).

The maths would get messy if we didn't do those things, so it turns out that the maths works out that the number of degrees that's the maximum the Earth can rotate through and still see Venus after the sun goes down is approximately :

$$heta = 90^circ-cos^{-1}left(frac {r_{venus}} {r_{earth}} ight)$$

Now $frac {r_{venus}} {r_{earth}} approx 0.72$ and this means $heta approx 46^circ$

If you think about $46^circ$ of rotation out of a quarther circle that's slightly more than half, and a quarter circle's worth of rotation of the Earth is about 6 hours, so that angle represents our ability to see Venus for (at most) three hours after sunset and three hours before sunrise.

This is also discussed in this article.

The technical term for these angles is elongation. The actual maximum elongation is slightly over $47^circ$ so the simplifications didn't do much damage to our estimate ! As it happens this year (in January) we had an elongation of Venus that was almost the maximum. It varies (due to the factors we simplified) between $45^circ$ and and slightly over $47^circ$.

Before we begin: how far a planet is seen from the Sun is called elongation, and it's measured in degrees. 0° elongation means it's right on top of the Sun (or behind); 180° elongation means it's opposite to the Sun (it's highest in the sky at midnight, when the Sun is on the other side of the Earth).

https://en.wikipedia.org/wiki/Elongation_(astronomy)

See the image below, where the Sun and the Earth are shown, along with an inferior planet (such as Mercury) and a superior planet (such as Mars). Elongation is the angle marked ε.

How can you see it at night?

Both Venus and Mercury are always seen close to the Sun. You can never see them at midnight, true. But you can see them during twilight, or, in Venus' case, shortly after nightfall (and then it sets quickly), or shortly before dawn in the morning (and then it's masked by the light of day). This is not a paradox or an impossibility. Here's why:

Mercury in particular can only be seen during twilight, very close to sunset or sunrise. Its orbit is so close to the Sun in space (only 39% the size of Earth's orbit), it does appear very close to the Sun even in the sky as seen from Earth. You could not see it during the day, of course, because the sky is so bright. But during twilight you can sometimes see it peeking just to the side of the Sun, very briefly - then it either sets in the West, or is swallowed by the light of day.

The greatest elongation that Mercury can achieve is 28°. Hold your arm straight out in front of you and make a fist; twice the size of your fist is nearly 28°. But even that's quite exceptional; most of the time Mercury stays closer to the Sun, closer than half of that angle (less than one fist).

So I should make it very clear: it's very rare that you can actually see Mercury with your naked eyes. It pretty much has to be right at maximum elongation. I've observed its phases (just like the Moon, or Venus) in a small dobsonian telescope a couple times; at max elongation it's close to the first quarter phase, or last quarter, and it looks like a very tiny replica of the Moon seen at that same phase. Kind of like this (except in my small telescope no craters or mountains were visible, because the image was just too tiny):

https://en.wikipedia.org/wiki/Planetary_phase

Venus' orbit is quite a bit wider, about 72% the size of Earth's own orbit. So it can swing ahead or behind the Sun quite widely. But that's all it can do - swing ahead or behind. It can never go "all the way around" the Earth. You can never see it at midnight, when the Sun is on the other side of Earth.

Venus' maximum elongation is 47°. Stretch your arm out and make a fist; now stick your thumb and your pinky sideways as far as they go (like the "hang loose" gesture, but stick them out all the way). The span from tip to tip is about 25°; twice that span is the maximum elongation of Venus.

Now imagine Venus at maximum elongation - two "hang loose" hand spans. The Sun has already set in the West about 1 hour and 40 minutes ago, so this is during the night, it's dark already, and now the Sun is one "hang loose" hand span below horizon. But Venus is at maximum elongation, which means it's one handspan above horizon. That's quite hight in the sky actually, you can see it pretty well.

So, there you have it. You can actually see Venus during the night. Not for long, because it still can't wander off too far from the Sun. It must remain within two "hang loose" hand spans from the Sun, or less than that distance, at all times. So Venus itself will set in the West soon after you see it. It cannot hang around until midnight.

Venus also shows phases, just like the Moon or Mercury. I've watched those too in my telescopes.

You can get more precise angle measurements if you can use an old-school marine sextant, like captains on ships back in the day. The fist and "hang loose" gesture techniques are just approximations. Or just get a protractor and tape two straws to it at the desired angle, and sight along the straws to estimate the angle in the sky.

The superior planets (Mars, Jupiter, etc) are not like that. Their orbits are larger than Earth's own orbit. So they can actually be seen, once in a while, high in the sky at midnight, when the Sun is on the opposite side of Earth.

Please refer to the diagram at the top of this reply, it's quite self-explanatory.

So, as you can see, the standard solar system model in astronomy is in excellent agreement with what you can see with your own eyes. There is no disagreement between observation and the model - if there was, the model would be fixed. That's how science works.

## Mercury and Venus to be visible tonight: How to see

### Venus: Life could be discovered by spacecraft says scientist

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The Moon is looking progressively dimmer this week, making stargazing opportunities more pronounced. Amateur astronomers and stargazers will be no more excited than the opportunity to see Mercury and Venus this evening. The two planets are the innermost celestial bodies in the solar system, with Earth coming next in the pecking order.

### How to see Venus and Mercury tonight

As Venus and Mercury are on the inside, relative to Earth's positioning from the Sun, they will only be visible for a few hours after sunset.

This is because as one side of Earth reaches night time, it is facing away from the Sun.

This obviously makes the two planets impossible to see.

However, there is a period just after sunset when Venus and Mercury will both be visible.

Mercury and Venus to be visible tonight: How to see (Image: GETTY)

The solar system (Image: GETTY)

Venus will be just next to the rising Moon on May 12.

While Venus will be easy to spot, to find Mercury is slightly trickier.

To do so, look at the waxing crescent Moon and follow it straight up around 45 minutes after sunset.

In the UK, the Sun will set at 20:42 BST.

How to see Venus and Mercury after sunset (Image: EARTHSKY)

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According to Time and Date, Venus will be visible until 21:49 while Mercury can be seen until 22:52.

The two planets will appear as if they are merely bright stars.

Earthsky said: "No matter where you live, you&rsquoll need an unobstructed horizon in the direction of sunset to increase your chances of catching the exceedingly thin young moon and Venus low in the sky and near the horizon, after sunset May 12.

"Even though the moon and Venus rank as the second-brightest and third-brightest celestial bodies to light up the heavens, after the sun, the brilliant twosome must compete with the evening twilight glow in the west.

Venus facts and figures (Image: EXPRESS)

### Trending

"And you can&rsquot wait to see them until twilight fades: the moon and Venus will follow the sun beneath the horizon before nightfall.

"If you miss the moon and/or Venus on May 12, try again on May 13, as a wider yet still slender lunar crescent shines higher up at sunset, and stays out longer after darkness falls.

"What&rsquos more, the illuminated side of the moon points at Venus, and you&rsquore more likely to catch the soft glow of earthshine adorning the dark (nighttime) side of the Moon."

## Why does Venus have phases like the Moon?

As the planet races around the Sun, it's Earth-facing side appears to change.

Much like the monthly lunar phases, Venus turns from a fully lit planet to a thin sliver of crescent-shaped light.

Mr Eagle has been tracking this change in Venus's appearance all month.

You can see just how much the planet has changed between April 13 and April 22 in the astronomer's photos.

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Mr Eagle said: "Venus orbits closer to the Sun than the Earth and is currently moving closer to us at the moment, causing it to grow steadily in size.

The changing angle of sunlight causes it to show phases

Dave Eagle, Astronomer

"As Venus moves between Earth and the Sun, the changing angle of sunlight causes it to show phases similar to those of the Moon.

"Almost day to day we can see Venus getting steadily bigger and the crescent phase getting thinner as it moves closer to the Sun.

"Venus gets so big, that you can see the shape of the planet using a simple pair of binoculars."

For a better view, however, the astronomer suggests using a small telescope for the better magnification.

Venus at night: Interesting facts and figures about Venus (Image: EXPRESS)

Venus at night: The planet's thick cloud coverage makes it incredible very reflective (Image: NASA)

Venus will continue to move closer to the Sun in the coming weeks.

The planet will appear lower and lower in the evening sky every night.

By the end of May, Venus will completely disappear into the twilight.

But you can still spot the planet now if you wait until sunset.

Simply look to the western skies where Venus will shine incredibly brightly near the constellation Taurus.

Venus is so bright when seen from Earth because its dense cloud coverage reflects up to 70 percent of all sunlight back into space.

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Mr Eagle said: "Venus is perpetually covered in white clouds. These reflect lots of sunlight back to us, this is what makes the planet extremely bright.

"So bright in fact, that it can be seen with the naked eye during the day, if you know where to look.

"Please ensure you do not look at the Sun, even with binoculars or a telescope.

"These clouds do make it impossible for us to observe the surface of the planet with our telescopes, so we can only ever view a blank disk."

Mr Eagle is an amateur astronomer and planetarium operator, which tours around schools, and runs the free Virtual Astronomy club.

## Venus is Especially Bright Right Now

Venus is always the second-brightest object in the night sky after the moon, which is why it has the nicknames "Morning Star" and "Evening Star," depending on when it’s visible. On March 24, Venus will reach its greatest eastern elongation, which is the night when it appears to be as far from the sun as it ever gets. Venus will be visible throughout the next month, and it will be at its brightest on April 27. After that, it will get closer to the sun before it finally gets lost in its glare and consequently disappears from view during early June 2020.

Before it goes, there’s time for brilliant Venus to put on one last big show on May 22, when it will shine right next to Mercury 𠅎merging from behind the sun — just after sunset.

## Tracking Venus In The Evening Sky Is A Great Activity For Kids

The International Space Station in a dawn pass, as it flies away to the east after passing overhead . [+] This was the morning of July 15, 2017 Blended in are images taken 20 minutes later of a pair of Iridium satellite flares in the dawn, the one below Iridium 54 being the first to appear, at a predicted magnitude of -7, while the one above Iridium 90 appeared one minute later at magnitude -3 Venus is the bright object at lower left in the dawn twilight above Aldbaran and below the Pleaides Capella is at far left The waning Moon is overexposed at far right This is a bit of cheat as the Iridiums were taken later than the ISS shots, but with the camera not moved and shooting a time-lapse through the entire sequence, from ISS appearance until the expected Iridium appearances later The sky for the Iridiums was brighter and bluer than for the ISS set, so that had to be corrected for in brightness and selective colour adjustments This is a useful image for comparing the ISS and Iridiums to Venus for brightness However, by the time the ISS got into the east here, it had dimmed quite a bit from its peak in brightness overhead The set for the Iridiums is a composite of 8 exposures, all 10 second exposures at f/25 with the Rokinon 14mm SP and Canon 6D The set for the ISS trail is a composite stack of 24 exposures for the ISS, masked onto a single background image of the sky taken just before the ISS entered the frame This kept the stars as points rather than trails, while the ISS trailed across the sky The gaps are from the 2 second interval between 10-second exposures All with the Canon 6D and 14mm Rokinon lens at f/25. (Photo by: VW Pics/Universal Images Group via Getty Images)

Universal Images Group via Getty Images

If you are among the millions staying home with their children at the moment, you might be wondering about some activity (any activity) to keep the younglings a bit occupied. One possibility would be to do a bit of naked-eye astronomy. You could start by looking for Venus in the evening sky.

Venus orbits the Sun at a distance closer than Earth, which means we always see the planet relatively close to the Sun. You will never see Venus high overhead in the middle of the night because the Earth is never between Venus and the Sun. Because of this, when Venus is visible it is typically seen in the western sky just after sunset, or in the eastern sky just before sunrise. It tends to be very bright during these times, which is why it's often called the evening or morning star.

Greatest elongation for an inferior planet.

Wikipedia user Wmheric, CC BY-SA 3.0

Currently, Venus is in the evening sky. If you look to the west after sunset, it will look like a very bright star. But unlike stars, it won't twinkle. It should be very easy to spot for two reasons. The first is that it is close to the Spring Equinox. This means the ecliptic (the orbital plane of the solar system) is oriented away from the horizon in the northern hemisphere. The second is that Venus is approaching greatest elongation.

Greatest elongation occurs when Venus reaches its greatest angle from the Sun. For Venus that's about 46°, and it occurs this year on March 24. If you have a pair of binoculars or a small telescope, you can also see Venus as a crescent shape. When Venus reaches greatest elongation, it will be a half-crescent, and then it will become a thinner crescent as its angle from the Sun decreases.

## Jupiter

Jupiter &mdash is brilliant (magnitude -2.4) in eastern Capricornus, and positioned well to the east (left) of dimmer Saturn. Beginning soon after 2 a.m. local daylight time on June 1, cast your gaze low toward the east-southeast and you'll see a waning gibbous moon and glowing prominently about 6 degrees to its upper left will be Jupiter. Both are well up in the southeast as dawn begins. During the late evening hours of June 28, the moon again pays Jupiter a visit. At 11:30 p.m., low in the east-southeast you'll see Jupiter shining 6.5 degrees to the upper right of the waxing gibbous moon.

## Bright Planet Venus Has Phases Like the Moon

The brilliant planet Venus is now a beautiful evening "star" in the late-fall twilight, shining brightly in the southwest through the purple dusk. But did you know Venus has phases like the moon that are visible in telescopes?

Weather permitting, Venus is the first planet night sky observers can spot, and it is even visible before sunset if you know just where to look in the southwest sky. The planet is gaining altitude in the twilight, boldly showing itself off after six months of hiding behind any inconvenient obstructions near the southwestern horizon.

Venus is brightening too, since it is speeding toward Earth as it catches up to us in its faster, inner orbit around the sun. [Weirdest Facts About Venus]

Phases of Venus revealed

As Venus travels around the sun inside the Earth's orbit, it alternates regularly from evening to morning sky and back. It typically spends about 9 1/2 months as an "evening star" and about the same length of time as a "morning star."

Some ancient astronomers actually thought they were seeing two different celestial bodies. They named the morning star after Phosphorus, the harbinger of light, and the evening star for Hesperus, the son of Atlas. It was the Greek philosopher and mathematician Pythagoras who first realized that Phosphorus and Hesperus was one and the same object.

To the ancients, such behavior was puzzling and was not really understood until the time of the famed 17th century astronomy Galileo Galilee. After moving to Pisa in the autumn of 1610, Galileo started observing Venus through his crude telescope. One evening he noticed that a small slice seemed to be missing from Venus' disk.

After several more months, Venus appeared in the shape of a crescent &mdash in other words, it seemed to display the same behavior as the phases of the moon. This was a major discovery, which ultimately helped to deliver a deathblow to the long-held concept of an Earth-centered universe.

Venus' path around the sun

Venus wanders only a limited distance east or west of the sun, since, like Mercury, it is an "inferior" planet (orbiting the sun more closely than Earth does). Watching its movement is akin to watching an auto race from the grandstand: All the action takes place in front of you and it&rsquos necessary to turn only a limited amount either way to see it at all. In contrast, for "superior" planets (those located in orbits beyond the Earth from the sun), viewers on Earth are like the pit crews inside the racetrack who must turn in all directions to follow the cars.

When Venus is on the opposite side of the sun from the Earth, it appears full (or nearly so) and rather small because it is far away. But because Venus moves with a greater velocity around the sun than the Earth, it gradually gets closer and looms progressively larger in apparent size. The angle of sunlight striking it as seen from our Earthly vantage point also appears to change as well.

Ultimately, as Venus prepares to pass between the Earth and the sun it appears as a thinning crescent. And since at this point in its orbit it is nearly six times closer to us compared to when it was on the opposite side of the Sun, it appears much larger to us as well.

Here then, is a schedule of how Venus&rsquo appearance has &mdash and will &mdash change during the coming weeks and months:

2013 Nov. 1, Greatest Eastern Elongation: Venus passed that point in the sky where it attained its greatest angular distance (47º) from the Sun last Friday and now sets about 2 1/2 hours after sundown. In our solar system geometry, Venus made a right angle with both the sun and Earth. In terms of apparent size, Venus now appears more than twice as large as it was at the end of July.

In a small telescope, Venus now closely resembles a dazzling silvery-white "half-moon." In the nights that follow it gradually becomes a fat crescent while growing ever larger as it swings around in its orbit closer to Earth.

2013 Nov. 6: Venus and the crescent Moon will make for an eye-catching sight in the west-southwest sky right after sunset. Venus will shine well below and to the left of the slender sunlit sliver (13-percent illuminated) of the moon. Observers should also be able to see the full globe of the moon, its darkened portion glowing with a bluish-gray hue interposed between the sunlit crescent and not much darker sky.

This vision is sometimes called "the old moon in the young moon's arms." Leonardo da Vinci (1452-1519) was the first to recognize it as earthshine. That dim bluish-gray light is light from the Earth reflected back to the moon.

The Earth's light of course is reflected sunlight, so earthshine is really sunlight which is reflected off Earth to the moon and reflected back to Earth. Another, similar pairing-off between the Moon and Venus will take place on the evening of Dec. 5.

2013 Dec. 6, Greatest Illuminated Extent/Greatest Brilliancy: This is the "compromise phase" between the time that Venus appears full, but tiny and when it appears almost six times larger but is just a hairline crescent. The greatest amount of illuminated surface area combined with a moderately large angular size makes Venus now appear truly dazzling, shining 25 times brighter than Sirius, the brightest star and setting nearly three hours after the sun.

Venus appears so bright now that it can be seen easily with the naked eye in a deep blue, haze-free afternoon sky. It continues to approach the Earth while appearing to curve back in toward the Sun in our sky. In a telescope it is now a big, beautiful crescent that grows larger and thinner with each passing night.

The crescent can now be glimpsed even in steadily held binoculars. Venus now stands 37 million miles from the Earth. Its disk appears 25-percent illuminated and about 35 percent larger in size than it did just one month ago.

2013 Dec. 21, Disk 12-percent illuminated: The crescent of Venus continues to narrow, but because it also continues to approach our Earth, it appears to greatly lengthen as well. It's now 29 million miles away, but is also now in a rapid plunge down the sky toward the sun. It's now setting just over two hours after sunset.

This is a good time to compare the appearance of Venus' two cusps. Can you make out the crescent's "cusp extensions" &mdash the thread-like wisps of light extending beyond the crescent's points?

2013 Dec. 28, Disk only 6-percent illuminated: It is now critical to try and locate Venus as early as possible when it is still high in the sky in a steady atmosphere. Observing well before sunset is best. At sunset as seen from mid-northern latitudes, Venus stands about 15 degrees above the southwest horizon and sets about 100 minutes later. Note: Your fist at arm's length covers 10 degrees of sky.

By this time, Venus is less than 27 million miles from the Earth and is becoming more and more aligned between our planet and the sun. As such, Venus is turning more and more of its dark side toward us. A week from now, it will be all but gone from the evening sky.

2014 Jan. 11, Inferior Conjunction: Venus will finally transition from an evening to morning star and will appear to pass between the Earth and the sun on this day. By the morning of Jan. 17 Venus is emerging as a new morning “star” rising in the east-southeast at mid-dawn.

By this time, Venus can be found about 3 degrees above the horizon a half-hour before sunrise. A line from the star Deneb, in Cygnus through the star Altair, in Aquila points right at it. After another week you should see it easily from anywhere with an open east-southeastern view 45 minutes to an hour before sunrise.

## Mercury and Venus will be at their closest until 2033 tonight, but may be hard to spot

If you're up for an observing challenge, Venus and Mercury will meet in the night sky Friday (May 28) for their closest encounter until Nov. 5, 2033.

The pair of planets will be visible low in the western sky for roughly 30 to 40 minutes after sunset, according to EarthSky. Observing will be tough given you may be competing with buildings and air pollution to see the planets, so bring binoculars if you can.

Sky & Telescope suggests looking west-northwest and starting with the bright stars Pollux and Castor, which are the heads of the Gemini constellation "twins." Slightly below Pollux and to your left, assuming you're gazing with the naked eye, you'll see Mars.

Follow the right-hand side of Gemini towards the horizon, and just below and to the right, you should see Mercury and Venus a mere 0.4 degrees apart. (As a bonus, the bright red star Betelgeuse is just barely above the horizon, so you may be able to see that too.)

You'll more likely see Venus first as it's shining at a brilliant magnitude -3.8, similar to the International Space Station at its best. "Mercury has dwindled to a mere magnitude +2.3, only 1/275 as bright," Sky & Telescope said. "So bring binoculars or a telescope to pick Mercury out of the skyglow."

The planets will remain relatively close in the sky for a few days, before Venus continues to climb away form the sun and Mercury sinks into the horizon. Mercury will reappear as a morning "star" in late June or early July 2021, EarthSky said, while Venus will remain an evening "star" through 2021.

Conjunctions like the Venus-Mercury encounter are regular events in the sky as the planets line up with Earth in their respective orbits. Over the Memorial Day weekend, there are a couple of other night sky events you can enjoy: a double shadow transit on Jupiter (Friday, May 28) and a gibbous moon near Saturn and Jupiter in the predawn sky of Monday (May 31).