Night sky

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The term night sky , usually associated with astronomy from Earth, refers to the appearance of celestial bodies such as stars, planets, and Moon at night, seen in the sunny sky between sunset and sunrise, The sun is under the horizon.

Natural light sources in the night sky include moonlight, starlight, and airflow, depending on location and time. Aurorae illuminates the sky above the polar circle. Sometimes, large coronal mass bursts from the Sun or just high solar wind levels can extend the phenomenon to the Equator.

The night sky and study of it have a historic place both in ancient and modern cultures. In the past, for example, farmers have used the status of the night sky as a calendar to determine when to plant crops. Many cultures have attracted the constellation of stars in the sky, using them in connection with legends and mythology about their gods.

The developed astrological belief is generally based on the belief that the relationship between heavenly bodies influences or conveys information about events on Earth. The scientific study of heavenly bodies seen at night occurs in the observational astronomical sciences.

The visibility of celestial bodies in the night sky is influenced by light pollution. The presence of the Moon in the night sky has historically hindered astronomical observations by increasing the amount of ambient brightness. With the advent of artificial light sources, light pollution has become a growing problem to see the night sky. Optical filters and lamp modifications can help alleviate this problem, but for optimal views, both amateur and professional astronomers look for locations far from urban skyglow.

Video Night sky

Brightness

The fact that the sky is not completely dark at night, even without moonlight and city lights, can easily be observed, because if the sky were really dark, one would not be able to see the silhouette of objects against the sky..

The intensity of the sky varies greatly throughout the day and the underlying cause is also different. During the daytime when the sun is above the horizon of direct scattering of the sun (Rayleigh scattering) is a very dominant source of light. At dusk, the time period between sunset and sunrise, the situation becomes more complicated and further differentiation is needed. Twilight is divided into three segments according to the extent to which the sun is below the horizon in the 6 Ã‚ Â° segment.

After sunset the civil twilight sets, and ends when the sun drops more than 6 Ã‚ Â° below the horizon. This is followed by a nautical twilight, when the sun reaches a height of -6 Ã‚ Â° and -12 Ã‚ Â°, thereafter comes the dusk of astronomy defined as the period from -12 Ã‚ Â° to -18 Ã‚ Â°. As the sun drops more than 18 Ã‚ Â° below the skyline generally reaches its minimum brightness.

Some sources can be identified as a source of intrinsic brightness of the sky, ie airflow, indirect scattering of sunlight, starlight scattering, and artificial light pollution.

Maps Night sky

Visual presentation

Depending on the local sky cloud cover, pollution, humidity, and light pollution levels, the stars visible to the unaided naked eye appear as hundreds, thousands or tens of thousands of dots of white light in the black sky that are almost approaching along with some vague nebula or light clouds. In ancient times the stars were often assumed to be equidistant on the dome above the earth because they were too far away for stereopsis to offer depth clues. The range of stars seen in colors from blue (hot) to red (cold), but with little dots like deceitful light, most look white because they stimulate stem cells without triggering the cone cells. If it is very dark and the sky object is very interesting, the vision that is avoided can help.

The stars of the night sky can not be counted without help because they are so numerous and there is no way to track what has been calculated and what is not. Further complicating the count, the dim stars may appear and disappear depending on exactly where the observer is looking. The result is an impressive impression of the star field.

Since the best-performing stars are from dark places away from city lights, dark adaptations are important to achieve and maintain. It takes a few minutes for the eyes to adjust to the darkness required to see the most stars, and the environment on the ground is hard to see. A red flashlight (torch) can be used to illuminate a star chart, telescope section, and the like without damaging dark adaptations. (See Purkinje effect).

Constellation

There are no signs in the night sky, although there are many sky maps to assist stargazers in identifying constellations and other celestial bodies. The constellations stand out because their stars tend to be lighter than the other nearby stars in the sky. Different cultures have created different groupings of constellations based on different interpretations of the pattern of more or less random points in the sky. The constellations are identified without regard to the distance to each star, but as if they were all dots on the dome.

Orion is one of the most prominent and recognizable stars. The Big Dipper (which has a variety of other names) is helpful for navigating the Northern Hemisphere as it points to Polaris, the northern star.

The polar stars are special because they are roughly parallel to the axis of rotation of the Earth so that they seem to stay in one place while the other stars revolve around them throughout the night (or a year).

Planet

The planet, named for the Greek word for "wandering," processes through the plane of stars a little every day, executes loops with time scales depending on the planet's length of the year or the orbital period around the solar system. The planet, with the naked eye, appears as a spot of light in the sky with varying brightness. The planet shines because sunlight reflects or splits from the planet's surface or atmosphere. So the sun-planet-earth position relative determines the planet's brightness. With good telescopes or binoculars, planets appear as discs that show limited size, and it is possible to observe orbits orbiting in the shadows to the surface of the host planet. Venus is the most prominent planet, often called the "morning star" or "night star" because it is brighter than the stars and is often the only "star" visible near sunrise or sunset, depending on its location in its orbit. Mercury, Mars, Jupiter, and Saturn are also visible to the naked eye.

Moon

Earth's Moon is a gray disc in the sky with a crater visible to the naked eye. It stretches, depending on the exact location, 29-33 minute arc - which is roughly the size of a small arm, and easily identifiable. Over 28 days, the moon passes through a full cycle of lunar phase. People can usually identify the phase in a few days by looking at the moon. Unlike stars and most planets, the light reflected from the moon is bright enough to be seen during the day. (Venus can sometimes be seen even after sunrise.)

Some of the most spectacular months come during the full moon phase near sunset or sunrise. The moon on the horizon benefits from the illusion of the moon which makes it appear larger. The light reflected from the moon traveling through the atmosphere also colored the orange and/or red moon.

Comet

Comets rarely come to the night sky. The comet is illuminated by the sun, and its tail extends from the sun. Comets with tails that look very unusual - large comets appear about once in a decade. They tend to be seen just before sunrise or after sunset because they are their time close enough to the sun to show the tail.

Clouds

Clouds obscure the views of other objects in the sky, although different cloud thicknesses have different effects. A very thin cirrus cloud in front of the moon may produce a rainbow-colored ring around the moon. Stars and planets are too small or dim to take this effect, and vice versa only dimmed (often to the point of transparency). The thicker cloudcover obscures the entire celestial object, making the sky black or reflecting back the city light. Clouds are often close enough to gain some deep perception, although they are hard to see without moonlight or light pollution.

Other objects

On dark and dark nights in unpolluted areas, when the moon is thin or below the horizon, the Milky Way, a band that looks like white dust, can be seen.

Shortly after sunset and before sunrise, artificial satellites often look like stars - similar in brightness and size - but move relatively quickly. Those who fly in low Earth orbit across the sky in minutes. Some satellites, including space debris, appear to flicker or have periodic fluctuations in brightness as they rotate.

Meteors (commonly known as falling stars) swing across the sky very rarely. During a meteor shower, they may average one minute at irregular intervals, but instead their appearance is a random shock. Meteors will occasionally make a bright and fast trail in the sky, and they can be very bright compared to the night sky.

Aircraft are also visible at night, can be distinguished by the distance from other objects because their lights blink.