 | This article relies largely or entirely on a single source .(May 2007) |
A Sun chart is a graph of the ecliptic of the Sun through the sky throughout the year at a particular latitude. [1]
| | This article relies largely or entirely on a single source .(May 2007) |
A Sun chart is a graph of the ecliptic of the Sun through the sky throughout the year at a particular latitude. [1]
Most sun charts plot azimuth versus altitude throughout the days of the winter solstice and summer solstice, as well as a number of intervening days. Since the apparent movement of the Sun as viewed from Earth is nearly symmetrical about the solstice, plotting dates for one half of the year gives a good approximation for the rest of the year. Thus, to simplify the diagram, some sun charts show days for different months as the same, e.g. March 21 equals September 21. The accompanying sun chart for Berlin accounts for deviations in symmetry between the two halves of the year through the use of the analemma, represented by each figure eight on the chart.
The graph may show the entire horizon or only that half of the horizon closest to the equator. Sky view obstructions can be superimposed upon a Sun chart to obtain the insolation of a location.
Archaeoastronomy is the interdisciplinary or multidisciplinary study of how people in the past "have understood the phenomena in the sky, how they used these phenomena and what role the sky played in their cultures". Clive Ruggles argues it is misleading to consider archaeoastronomy to be the study of ancient astronomy, as modern astronomy is a scientific discipline, while archaeoastronomy considers symbolically rich cultural interpretations of phenomena in the sky by other cultures. It is often twinned with ethnoastronomy, the anthropological study of skywatching in contemporary societies. Archaeoastronomy is also closely associated with historical astronomy, the use of historical records of heavenly events to answer astronomical problems and the history of astronomy, which uses written records to evaluate past astronomical practice.
A solar equinox is a moment in time when the Sun crosses the Earth's equator, which is to say, appears directly above the equator, rather than north or south of the equator. On the day of the equinox, the Sun appears to rise "due east" and set "due west". This occurs twice each year, around 20 March and 23 September.
Concerning the lunar month of approximately 29.53 days as viewed from Earth, the lunar phase or Moon phase is the shape of the Moon's directly sunlit portion, which can be expressed quantitatively using areas or angles, or described qualitatively using the terminology of the four major phases and four minor phases.
A solstice is an event that occurs when the Sun appears to reach its most northerly or southerly excursion relative to the celestial equator on the celestial sphere. Two solstices occur annually, around June 21 and December 21. In many countries, the seasons of the year are determined by the solstices and the equinoxes.
In astronomy, an analemma is a diagram showing the position of the Sun in the sky as seen from a fixed location on Earth at the same mean solar time, as that position varies over the course of a year. The diagram will resemble a figure eight. Globes of Earth often display an analemma as a two-dimensional figure of equation of time vs. declination of the Sun.
The heliacal rising or star rise of a star occurs annually, or the similar phenomenon of a planet, when it first becomes visible above the eastern horizon at dawn just before sunrise after a complete orbit of the Earth around the Sun. Historically, the most important such rising is that of Sirius, which was an important feature of the Egyptian calendar and astronomical development. The rising of the Pleiades heralded the start of the Ancient Greek sailing season, using celestial navigation, as well as the farming season. Helical rising is one of several types of risings and settings, mostly they are grouped into morning and evening risings and settings of objects in the sky. Culmination in the evening and then morning is set apart by half a year, while on the other hand risings and settings in the evenings and the mornings are only at the equator set apart by half a year.
In observational astronomy, culmination is the passage of a celestial object across the observer's local meridian. These events were also known as meridian transits, used in timekeeping and navigation, and measured precisely using a transit telescope.
Sunset is the disappearance of the Sun below the horizon due to Earth's rotation. As viewed from everywhere on Earth, it is a phenomenon that happens once every 24 hours except in areas close to the poles. The equinox Sun sets due west at the moment of both the spring and autumn equinoxes. As viewed from the Northern Hemisphere, the Sun sets to the northwest in the spring and summer, and to the southwest in the autumn and winter; these seasons are reversed for the Southern Hemisphere.
Midnight sun is a natural phenomenon that occurs in the summer months in places north of the Arctic Circle or south of the Antarctic Circle, when the Sun remains visible at the local midnight. When midnight sun is seen in the Arctic, the Sun appears to move from left to right, but in Antarctica, the equivalent apparent motion is from right to left. This occurs at latitudes from 65°44' to 90° north or south, and does not stop exactly at the Arctic Circle or the Antarctic Circle, due to refraction.
Twilight is light produced by sunlight scattering in the upper atmosphere, when the Sun is below the horizon, which illuminates the lower atmosphere and the Earth's surface. The word twilight can also refer to the periods of time when this illumination occurs.
The night sky is the nighttime appearance of celestial objects like stars, planets, and the Moon, which are visible in a clear sky between sunset and sunrise, when the Sun is below the horizon.
Polar night is a phenomenon in the northernmost and southernmost regions of Earth where night lasts for more than 24 hours. This occurs only inside the polar circles. The opposite phenomenon, polar day, or midnight sun, occurs when the Sun remains above the horizon for more than 24 hours.
The March equinox or northward equinox is the equinox on the Earth when the subsolar point appears to leave the Southern Hemisphere and cross the celestial equator, heading northward as seen from Earth. The March equinox is known as the vernal equinox in the Northern Hemisphere and as the autumnal equinox in the Southern Hemisphere.
A lunar standstill or lunistice is when the moon reaches its furthest north or furthest south point during the course of a month. The declination at lunar standstill varies in a cycle 18.6 years long between 18.134° and 28.725°, due to lunar precession. These extremes are called the minor and major lunar standstills.
Manhattanhenge, also called the Manhattan Solstice, is an event during which the setting sun or the rising sun is aligned with the east–west streets of the main street grid of Manhattan, New York City. The astrophysicist Neil deGrasse Tyson claims to have coined the term, by analogy with Stonehenge. The sunsets and sunrises each align twice a year, on dates evenly spaced around the summer solstice and winter solstice. The sunset alignments occur around May 28 and July 13. The sunrise alignments occur around December 5 and January 8.
Daytime as observed on Earth is the period of the day during which a given location experiences natural illumination from direct sunlight. Daytime occurs when the Sun appears above the local horizon, that is, anywhere on the globe's hemisphere facing the Sun. In direct sunlight the movement of the sun can be recorded and observed using a sundial that casts a shadow that slowly moves during the day. Other planets and natural satellites that rotate relative to a luminous primary body, such as a local star, also experience daytime, but this article primarily discusses daytime on Earth.
Sun path, sometimes also called day arc, refers to the daily and seasonal arc-like path that the Sun appears to follow across the sky as the Earth rotates and orbits the Sun. The Sun's path affects the length of daytime experienced and amount of daylight received along a certain latitude during a given season.
A season is a division of the year based on changes in weather, ecology, and the number of daylight hours in a given region. On Earth, seasons are the result of the axial parallelism of Earth's tilted orbit around the Sun. In temperate and polar regions, the seasons are marked by changes in the intensity of sunlight that reaches the Earth's surface, variations of which may cause animals to undergo hibernation or to migrate, and plants to be dormant. Various cultures define the number and nature of seasons based on regional variations, and as such there are a number of both modern and historical cultures whose number of seasons varies.
The position of the Sun in the sky is a function of both the time and the geographic location of observation on Earth's surface. As Earth orbits the Sun over the course of a year, the Sun appears to move with respect to the fixed stars on the celestial sphere, along a circular path called the ecliptic.
The Arctic Circle is one of the two polar circles, and the most northerly of the five major circles of latitude as shown on maps of Earth. Its southern equivalent is the Antarctic Circle.
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