The position of the Arctic Circle is not fixed, but directly depends on the Earth's axial tilt, which fluctuates within a margin of 2 ° over a 40, 000 year period, notably due to tidal forces resulting from the orbit of the Moon.

In a solar calendar a year approximates Earth's tropical year ( that is, the time it takes for a complete cycle of seasons ), traditionally used to facilitate the planning of agricultural activities.

A 2005 report by the United Nations Food and Agriculture Organization ( FAO ) estimates that although the Earth's total forest area continues to decrease at about 13 million hectares per year, the global rate of deforestation has recently been slowing.

An equinox occurs twice a year ( around 20 March and 22 September ), when the tilt of the Earth's axis is inclined neither away from nor towards the Sun, the center of the Sun being in the same plane as the Earth's equator.

The concepts of the leap year and leap day are distinct from the leap second, which results from changes in the Earth's rotational speed.

As the planet is often reached by means of time travel, its relative present could conceivably exist anywhere in the Earth's past or future before the year 100 trillion, which the Time Lords never reached.

The heroic Avatar travels first to the year 1887, then on to Mars to rescue many of Earth's scientists, celebrities, and politicians stranded there by accident.

The direction of the Earth's axial tilt, as well as its angle relative to the plane of the Earth's orbit around the sun, remains very nearly constant over the course of a year ( both change very slowly over long time periods ).

In 1956, the second was redefined in terms of a year ( the period of the Earth's revolution around the Sun ) for a particular epoch because, by then, it had become recognized that the Earth's rotation on its own axis was not sufficiently uniform as a standard of time.

In this formula dn-3 is used, because in modern times Earth's perihelion, the closest approach to the Sun and therefore the maximum E < sub > ext </ sub > occurs around January 3 each year.

The uplift of the Earth's crust is continuing even today-2mm per year.

Vega is expected to become Earth's Pole star by year 26, 000 by some estimates.

Because the Earth's axis is tilted relative to its orbital plane, sunlight is incident at different angles at different times of the year.

Because the Earth's axis is tilted relative to its orbital plane, sunlight is incident at different angles at different times of the year.

Due to the Earth's axial tilt, the course of a year sees the passing of the seasons, marked by changes in weather, hours of daylight, and consequently vegetation and fertility.

A calendar year is an approximation of the Earth's orbital period in a given calendar.

It is estimated that, by the year 4000, the vernal equinox will fall back by one day in the Gregorian calendar, not because of this difference, but because of the slowing down of the Earth's rotation and the associated lengthening of the sidereal day.

Because of a " wobble " in the Earth's axis of rotation over a period of about 26, 000 years ( often called a " great year "), the rate at which the vernal equinox precesses in the heavens is approximately 0 deg, 0 min, 50. 23 seconds a year, drifting by one degree every 72 years.

There are also other perturbations such as Earth's wobble, but these are less than a second per year.

Its fundamental principle is that of balance-the energy that the Earth absorbs from the sun each year is equal to that which it loses back into space, but this however is not a balance precisely maintained in each latitude due to the varying strength of the sun in each " cell " resulting from the tilt of the Earth's axis in relation to its orbit.

For a brief period each year, the rays of the sun are warm enough to melt some of the snows piled a mile deep at the base of the headwalls, and then the pinnacles glisten in the daytime at high noon, and billions of gallons of water begin their slow seepage under the glaciers and across the rockstrewn hanging valleys on their long, meandering journey to the sea -- running east past the sky-carving massifs of Gurla Mandhata and Kemchenjunga, then turning south and curling down through the jungles of Assam, past the Khasi Hills, and into Bengal, past Sirinjani and Madaripur, until the hard water of the melting snows mingles with the soft drainage of fields and at length fans out to meld with the teeming salt depths of the Bay of Bengal.

North of the Arctic Circle, the sun is above the horizon for 24 continuous hours at least once per year ( and therefore visible at midnight ) and below the horizon for 24 continuous hours at least once per year.

The main reason students head to Mexico is the 18 year old drinking age ( versus 21 for the United States ), something that has been marketed by tour operators along with the sun and ocean.

They pointed out that astrologers have only a small knowledge of astronomy and that they often do not take into account basic features such as the precession of the equinoxes which would change the position of the sun with time ; they commented on the example of Elizabeth Teissier who claimed that " the sun ends up in the same place in the sky on the same date each year " as the basis for claims that two people with the same birthday but a number of years apart should be under the same planetary influence.

There are on average almost 300 days of sun and 700 mm of rain per year.

During the winter, storms blowing from the Sahara sometimes form dense dust clouds that obscure the sun ; however, sunny days are the norm year round.

His Tàichū (, " Grand Inception ") calendar of 104 BC had a year with the winter solstice in the 11th month and designated as intercalary any calendar month ( a month of 29 or 30 whole days ) during which the sun does not pass a principal term ( that is, remained within the same sign of the zodiac throughout ).

Though the fact of the irregularity of the lunar orbit was known in the 1st century BC, the starts of the months were calculated using the mean motions of both the sun and moon until 619, the second year of the Tang dynasty, when chronologists began to use true motions modeled using two offset opposing parabolas ( with small linear and cubic components ).

Since the Celtic year was based on both lunar and solar cycles, it is most likely that the holiday would be celebrated on the full moon nearest the midpoint between the winter solstice and vernal equinox, or when the primroses, dandelions, or other spring flowers rise up through the snow, or when the sun aligned with the passage tombs in the pre-Celtic megaliths.

A complete orbit around the sun takes one year or about 365 days ; it averages a speed of about 30 km / s ( 67, 000 mi / h ).

As the year progresses and the Earth moves around the sun, the North Pole gradually turns away from the sun until at midwinter it is facing away from the Sun to its maximum extent.

This line of reasoning fails at the North Pole, where the sun rises and sets only once per year, and all lines of longitude, and hence all time zones, converge.

In the Northern Hemisphere's summer months, when Ophiuchus is normally visible in the night sky, the constellation is actually not visible in the Arctic Circle because the sun does not set at that time of year north of the Arctic Circle.

Typical star densities in the centre of a cluster are about 1. 5 stars per cubic light year ; the stellar density near the sun is about 0. 003 stars per cubic light year.

Pytheas took the altitude of the sun at Massalia at noon on the longest day of the year and found that the tangent was the proportion of 120 ( the length of the gnōmōn ) to 1 / 5 less than 42 ( the length of the shadow ).

Phaëthon, son of the sun, struck by lightning changed into poplars and exuded tears every year, which is the source of amber ( a myth of Pausanias ).

The passage itself, in a number of notable instances, is aligned in such a way that the sun shines into the passage at a significant point in the year, for example at sunrise on the winter solstice or at sunset on the equinox.

19th-and 20th-century astronomical observations revealed that the mean solar day is slowly but measurably lengthening and the length of a tropical year is not entirely predictable either ; thus the sun – earth motion is no longer considered a suitable basis for definition.

Because the sun is low in the horizon for most of the year, it is difficult for plants to generate energy from photosynthesis.

The sun is indeed just above the horizon at these times on the shortest days of the year in northern Newfoundland-but not much farther north.

What is simply an opinion formed in defiance of the laws of human probability, whether or not it is later confirmed, has become by September of the election year `` a firm conviction ''.

During the past year, our long-range striking power, unmatched today in manned bombers, has taken on new strength as the Atlas intercontinental ballistic missile has entered the operational inventory.

Since 1953 California has led the nation in enacting guarantees that public business shall be publicly conducted, but not until this year did the lawmakers in Sacramento plug the remaining loopholes in the Brown Act.

Competition from other steamship lines has cut Cunard's share of sea passengers from one-third to one-fourth and this year the line showed a marked drop of profits on the Atlantic run.

Certainly it isn't making the President happy, and he has been doing his apologetic best to explain how the budget got into its unbalanced condition, how he intends to economize wherever he can and how he hopes to do better next year.

Intangible property is taxable wherever the owner has a place of abode the greater portion of the year.

It has been said that when local government revenues were mostly produced locally from the property tax, the lack of a uniform fiscal year was no great handicap ; ;

The President of the United States, pursuant to a Joint Resolution of Congress, has issued a proclamation each year since 1933 declaring May 22nd to be National Maritime Day.

The effective recognition of excellence and its nurture has to be learned and is not learned in a day, nor even in a year.

During the past year, great progress has been made by the weaving mills in creating new stretch and textured fabrics.

The school year does not end for any student until he has completed his last examination of the semester.

And yet, despite some disappointment with the performance of this first year of the new decade, 1960 has been a good year in many ways, with many overall measures of business having reached new peaks for the year as a whole.

The shift in sentiment from excessive optimism early in the year to the present mood of caution has probably been a good thing, in that it has prevented the accumulation of the burdensome inventories that have characterized many previous swings in the business cycle.

As the Juniors entered the ring, Mr. Spring, the announcer, stated over the public-address system that this was the 28th year that Westminster has held the Finals of the Junior Competition.

Next year 1962, at Westminster, the Bench Show Committee has raised the requirements so that a junior must win 3 or more Junior Classes in the open division only to qualify for Westminster.

Percy Roberts, a leading judge will not be at the International Show this year for the Junior Judging Contest as he has been invited to judge in Australia in March.

A beginner's shotgun has also been introduced this year.

One or two of the schools have a five year curriculum, but the usual pattern of American education has limited most of them to the four-year plan which seems to be the minimum in acceptable institutions.

Nineteen-sixty has been a baffling year for analysts of general business activity.

During much of the year the general level of business activity has moved along on a record-high plateau, but there have been persistent signs of slack in the economy.

Although the pause in the advance of general business activity this year has thus far been quite modest, it is hard to escape the conclusion that the softening process will continue into the first quarter of 1961 and possibly somewhat longer.