how much of the sky is visible over the course of a night

For an 11h45m night, that comes out to 38.0%, 29.9%, 22.0% for a = 10, 20, and 30 degrees respectively. If you consider that cos (90 − b) / 2 of the sky is never visible (because it's always below the horizon), these become 61.6%, 48.5%, 35.7% of the sky that you could ever see. These calculations were somewhat hasty...

Full Answer

How much of the sky can we see at any moment?

Putting aside the curvature of the Earth and refraction and terrain and so forth, we can say that at any moment, half the sky is available to view.

What is the fraction of the sky visible?

Giving us for our fraction of the sky visible: Plotting this function over large distances, we see that it behaves as we expect: It starts at 50% and goes to 100% as we get to distances a few earth radii out. But you were interested in very short distances: Here we can see the effect of small height changes.

What percentage of the sky is visible at the equator?

Over the course of 24 hours, the percentage of the entire celestial sphere that's available to view varies from 50% (at the poles) to 100% (at the equator). For a given latitude, this value is 50% + cos(|lat|) * 50%. But of course the sun blocks the sky during the course of a day.

How close to the surface can we see the sky?

In one limit, we can imagine being infinitely far away from the surface, where surely we will be able to see the whole sky. In the other limit, we can imagine being infinitesimally close to the surface, at which point our planet will appear to be an infinite wall and we will see precisely half of the surface.

How much of the sky is visible at night?

Putting aside the curvature of the Earth and refraction and terrain and so forth, we can say that at any moment, half the sky is available to view. Over the course of 24 hours, the percentage of the entire celestial sphere that's available to view varies from 50% (at the poles) to 100% (at the equator).

What percentage of the sky can you see from North Pole?

What fraction of the sky can be seen from the North Pole? Answer: 1/2 (that part above the celestial equator).

How much does the night sky change?

This change is due to the motion of the Earth in its orbit around the Sun. Each day a few stars are visible in the east that were not visible the night before. If you were to measure how much the sky "shifted" from one day to the next you would discover that it "shifts" approximately one degree per day.

What does the sky look like at night?

At night we see stars in a dark sky, and these stars make up our galaxy, the Milky Way. The Milky Way is made of a huge number of stars, including the Sun. Compared with other stars, the Sun actually isn't that bright, but it looks very bright to us because it's much closer to Earth than other stars are.

How many degrees of the sky can we see?

From the horizon to the point directly overhead (the zenith) would equal 90-degrees; from one horizon point through the zenith and continuing across to the opposite side of the sky would measure 180-degrees.

What percentage of stars can we see?

An extremely, yep, tiny little percentage. There are only about 5,000 stars visible to the naked, average, human eye, MinutePhysics points out. And, because the Earth itself gets in the way, you can only see about a half of those from where you stand.

Are stars still visible in the succeeding hours?

The stars therefore complete a full circle (360°) in 24 hours. (Of course, you normally can't see the stars during daylight, but they're still there and still following their circular paths, as you can confirm with a telescope or by getting above earth's atmosphere.)

Do we see the same stars every night?

The stars are not fixed, but are constantly moving. If you factor out the daily arcing motion of the stars across the sky due to the earth's rotation, you end up with a pattern of stars that seems to never change.

Why do stars rise 4 minutes earlier?

Because Earth moves around the Sun (roughly 1° per day), after one complete rotation of Earth relative to the stars, we do not see the Sun in the same position. Because our ordinary clocks are set to solar time, stars rise 4 minutes earlier each day.

What is the difference between day sky and night sky?

The daytime sky appears blue because air molecules scatter shorter wavelengths of sunlight more than longer ones (redder light). The night sky appears to be a mostly dark surface or region spangled with stars. The Sun and sometimes the Moon are visible in the daytime sky unless obscured by clouds.

Why is the night sky not bright?

Anything farther, and the light just wouldn't have had enough time to get there yet. Therefore, when we look at the night sky, we only see light coming from stars within about 13 billion light-years of us, and the total amount of light produced by all these stars is not enough to make the night sky particularly bright.

Why is the night sky so bright?

Instead, a new study suggests, the phenomena occur when four types of slow-moving, high-altitude atmospheric waves merge over a small region and, in turn, temporarily drive a 10-fold-or-stronger brightening of an ever-present glow in the upper atmosphere (green layer in the image above).

Where are the stars at the North Pole?

If you are standing at the North Pole, and compare what you see with your friend at the equator, then you see all the stars that are directly above his head, and all along the line that forms the equator, and you see all the stars north of that line. Similarly, Polaris is directly above your head, and Polaris is visible to your friend at the Equator.

How many magnitudes would Polaris extinction be?

suggests 3...4 magnitudes extinction at 4 degrees altitude... which would make Polaris hard to see.

Can you see stars at the equator?

I would think that you could only see stars that are "north" of a plane tangent to the Earth, and that you would not be able to see stars that are directly over the equator. The diagram you attached shows the "Theoretical Horizon" as just such a tangent plane. For values of h equal to a couple of meters, it seems like much of the night sky would be blocked out, much more than half, and that Polaris would NOT be visible at the equator when it is nearly straight up over the north pole.

Can you see more than one half of the celestial sphere?

At sea, you can see slightly more than one half of the celestial sphere... refraction of the atmosphere lets you see slightly below the horizon, neglecting crud in the air between you and whatever you are looking at.

Can you see stars on the other side of the Earth?

This is true. However, you would also be able to see stars that are on the other side of the Earth that your friend cannot see. Ignoring things like hills, mountains, and trees, you would be able to see Polaris if you stood at the equator. It would be very, very close to the horizon and would stay there as the Earth rotates. You would also be able to see all the way to the southern celestial pole.

Is parallax visible in space?

At the multi-lightyear distances of the stars, this parallax is not easily noticeable. At least not without high precision instruments out in space like the Hipparcos and Gaia space observatories. And even these rely on the much larger change in position that results from our orbit around the Sun.

Can you see everything at the north pole?

A person standing at the north pole would be able to see everything above the celestial equator all at once, but would never be able to see anything in the southern celestial hemisphere. The reverse is true for someone standing at the south pole.

How much of the sky can you see at cruising altitude?

Here I've plotted the semilog plot against the x axis. For instance, at the cruising altitude of a commercial plane (~ 38,000 ft), you can see 53% of the sky, a whole 3% more than on the ground from purely geometric considerations. This we could hope to notice over optical effects.

How much refraction can you see from the surface of an ocean?

In principle from the surface of a flat ocean you can see 2 π of the 4 π that is the full celestial sphere. However there is some refraction of the atmosphere (you can see that from the shape of the setting sun...) - this actually means you can see a little bit more than half the entire sky. At the level of the horizon the refraction is just over half a degree. From http://en.m.wikipedia.org/wiki/Atmospheric_refraction :

How long does it take for an object to orbit the Earth?

Visible objects in low-Earth orbit (such as the International Space Station) take about 90 minutes—5,400 seconds —to complete a single orbit. Unequivocally far beyond the mesosphere at 240-250 miles above Earth, such objects might provide a rough proxy for measuring the portion of blue "sky" that is visible.

How long does it take to see an object in low Earth orbit?

Now when viewed from their backyard, most people will estimate that an object in low-Earth orbit passes directly over a fixed location in about five to ten seconds. By this measure, from a single point on Earth you can usefully “see” 0.185% (about 2 tenths of one percent) of the local sky.

Ignoring refraction is a geometry problem?

Ignoring refraction (which will be important at the scales we discuss below, so ought not be ignored in actuality, see Floris' answer ), this is a geometry problem. Whenever you are trying to calculate a result, it is always good to start by reasoning out some limiting cases. In one limit, we can imagine being infinitely far away from the surface, where surely we will be able to see the whole sky. In the other limit, we can imagine being infinitesimally close to the surface, at which point our planet will appear to be an infinite wall and we will see precisely half of the surface. We expect the answer to be monotonic in between. Let's try to work it out.

What is the starting point of the radii of the Earth?

It starts at 50% and goes to 100% as we get to distances a few earth radii out.

Why does the night sky look like it has millions of stars?

Nick Greene. Updated June 15, 2018. The nighttime sky looks like it has millions of stars visible to observers. That's because we live in a galaxy that has hundreds of millions of them. However, we can't really see all of them with the naked eye from our backyards. It turns out that the skies of Earth have, at most, ...

What is the brightest star in the sky?

The Sun is magnitude -26.74 and is THE brightest star in our daytime sky. The dimmest magnitude anyone can detect with the naked eye is around magnitude 6. The "intrinsic magnitude" of a star is how bright it is due to its own temperature, regardless of distance.

What makes a star red?

Also, the materials that make up a star (that is, it's composition) can make it look red or blue or white or orange. Stars are primarily hydrogen, but they can have other elements in their atmospheres and interiors. For example, some stars that have a lot of the element carbon in their atmospheres look redder than other stars.

What would happen if a star was closer?

If it was closer, it would be brighter. A cooler, intrinsically dim star might look very bright to us if it was very close by. Most stargazers are interested in something called "visual (or apparent) magnitude", which is the brightness it will appear to the eye.

What would happen if we were in the center of the galaxy?

If our planet could be in the center of the galaxy, or perhaps in a globular cluster, the sky would shimmer with starlight. In fact, in a globular cluster, we might never have dark skies! In the center of the galaxy, we might be stuck in a cloud of gas and dust, or perhaps be subjected to forces from the black hole at its heart. So, in a way, while our location in the outskirts of the Milky Way reveals fewer stars to stargazers, it's a safer place to have a planet with dark skies.

What can we learn from stars?

So, what can be learned from the stars that observers CAN see? For one thing, people often notice that some stars appear white, while others are bluish, or orangey or reddish. Most, however, appear to be a dull white. Where does the color come from? The star's surface temperature gives a clue—the hotter they are, the more blue and white they are. The redder they are, the cooler they are. So, a blue-white star is hotter than a yellow or orange star, for example. Red stars are usually fairly cool (as stars go). It's important to remember, however, that a star's color isn't vivid, it's more likely very pale or pearlescent.

Why do stars look bright?

A star can look bright or dim depending on far away it is. But, it can also look bright because it's very hot. Distance AND temperature play a role in magnitude. A very hot, bright star that lies very far away from us appears dim to us.

What is the night sky map?

The Night Sky Map near the top of the page represents the sky above the selected location on a date and at a time of your choice. It allows you to easily locate a planet, the Moon, or the Sun and track their movements across the sky in the chosen time period. It also shows all solar and lunar eclipses.

Where is the compass needle on the night sky map?

Use the compass directions at the bottom to keep your bearings. On desktop computers, you can click the compass needle on the right to face north.

How to change the date on Night Sky Map?

The Interactive Night Sky Map defaults to the current date and time (real-time mode). Click on the calendar at the bottom of the animation to select a different date.

Why is a planet invisible?

There are several reasons why a planet or object may remain invisible even though it rises above the horizon. It may be too bright at night or the object may only rise above the horizon during daylight hours.

What does the curved line on a map mean?

The curved line represents the object's apparent path across the sky during the selected date (noon to noon), as seen from the selected location. The solid portion of the line shows the object's movement before the currently shown point in time; the dotted portion shows its movement after that moment. The path line can be switched on or off in the Settings.

How to use 360 degree animation?

On most mobile devices, the animation offers a 360-degree mode which allows you to steer the sky map by pointing your device at the sky. To activate, simply tap on on the right and use your device like a camera to control the map's orientation .

Why does the Sun move in the sky?

However, since the planets and the Moon are in constant motion and the Sun also shifts its apparent position each day in relation to the Earth, their position in the sky changes slightly from one noon to the next.

What is the light that shines on the face of the Moon that we never see?

the sunlight that shines on the face of the Moon that we never see. the light from the Moon that illuminates Earth's surface at night. the light we see at dawn just before the Sun rises. sunlight reflected by Earth that illuminates the dark portion of the Moon.

What is the line up of the Earth Moon and Sun needed for a lunar eclipse?

The line-up of the Earth Moon and Sun needed for a lunar eclipse happens many many times more often than what is needed for a solar eclipse. A total lunar eclipse is visible over a much larger part of the Earth's surface than a total solar eclipse. A total lunar eclipse is visible over a much larger part of the Earth's surface than ...

What is the name of the angle the Moon makes with the Sun?

When the Sun and Moon are lined up and pull together the tides they raise are called: low tides. prolate tides.

How does a planet move?

The planet moves backward through the sky over the course of a night. The planet appears to move westward with respect to the stars over a period of many nights. The planet moves backward in its orbit around the Sun. The planet appears to move westward with respect to the stars over a period of many nights.

What gets in the way of the Moon's light and covers up parts of it?

Clouds get in the way of the Moon's light and cover up parts of it.

How long is the time between new moons?

The time between new Moons is two weeks.

Where is the umbra of the Moon?

The Moon's umbra must touch the area where you are located. Earth must be near aphelion in its orbit of the Sun. Earth must lie completely within the Moon's prenumbra. Earth must lie completely within the Moon's umbra. The Moon's umbra must touch the area where you are located.

Why are the constellations we gaze at today the same?

This difference is due to the Earth’s natural axial tilt. Eight degrees may not seem like much, but because of this angle, the constellations we gaze at today are the same, yet completely different from the ones our ancestors looked up at.

What is the hottest object in the universe?

Located in the Canis Majoris constellation, Sirius burns bluish-white, and is one of the hottest objects in the universe with a surface temperature of 17,400°F (9,667°C). Sirius is nearly 40 times brighter than our Sun.

Which star is brighter, Polaris or Sirius?

Interestingly, Polaris ’ dependability is why it is commonly mistaken as the brightest star, but Sirius actually takes that crown—find it below the Gemini constellation, at the 7HR latitude and -20° longitude coordinates on the visualization. Located in the Canis Majoris constellation, Sirius burns bluish-white, and is one of the hottest objects in the universe with a surface temperature of 17,400°F (9,667°C). Sirius is nearly 40 times brighter than our Sun.

How long has the G20 energy mix changed?

Visualizing 50+ Years of the G20’s Energy Mix (1965–2019) Over the last 50 years, the energy mix of G20 countries has changed drastically in some ways. With many countries and regions pledging to move away from fossil fuels and towards cleaner sources of energy, the overall energy mix is becoming more diversified.

What does the red line on the constellation signify?

The red lines on the visualization signify the constellations officially recognized by the International Astronomical Union (IAU) in 1922. Its ancient Greek origins are recorded on the same map as the blue lines, from which the modern constellation boundaries are based.

How have stars fascinated humans?

The stars have fascinated humanity since the beginning of civilization, from using them to track the different seasons, to relying on them to navigate thousands of miles on the open ocean.

Where are the two spiral galaxies located?

The only two visible spiral galaxies, Andromeda and Pinwheel, are located close between 0-2HR latitude and 30°-40° longitude.