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.

Other formula-based calendars can have lengths which are further out of step with the solar cycle, for example, the Julian calendar has an average length of 365. 25 days, and the Hebrew calendar has an average length of 365. 2425

The sìfēn 四分 ( quarter remainder ) calendar, which began about 484 BC, was the first calculated Chinese calendar, so named because it used a solar year of 365¼ days ( the same as the 1st century BC Julian Calendar of Rome ), along with a 19-year ( 235-month ) Rule Cycle zhang 章, known in the West as the Metonic cycle.

The standardization of time is a human convention based on the solar cycle or calendar.

The large-scale structure of the corona changes over the 11-year solar cycle and becomes particularly simple during the minimum period, when the magnetic field of the Sun is almost similar to a dipolar configuration ( plus a quadrupolar component ).

The fraction of the solar surface covered by bright points varies with the solar cycle.

The result of the Sun's differential rotation is that the active regions always arise in two bands parallel to the equator and their extension increases during the periods of maximum of the solar cycle, while they almost disappear during each minimum.

Therefore the quiet Sun always coincides with the equatorial zone and its surface is lower during the maximum of the solar cycle.

Approaching the minimum of the solar cycle ( also named butterfly cycle ), the extension of the quiet Sun increases until it covers the whole disk surface excluding some bright points on the hemisphere and the poles, where there are the coronal holes.

The lunar year consists of 30-day and 29-day lunar months, generally alternating, with an embolismic month added periodically to bring the lunar cycle into line with the solar cycle.

Because the Julian calendar's implicit solar year has drifted further over the centuries than those of the Gregorian or Hebrew calendars, Julian Easter is a lunation later than Gregorian Easter in five years out of nineteen, namely years 3, 8, 11, 14, and 19 of the Christian cycle.

This cumulative effect of the errors in the Julian calendar's solar year and lunar age has led to the often-repeated, but false, belief that the Julian cycle includes an explicit rule requiring Easter always to follow Jewish Passover.

Because of the roughly eleven-day difference between twelve lunar months and one solar year, the length of the Hebrew calendar year varies in the repeating 19-year Metonic cycle of 235 lunar months, with the intercalary month added according to defined rules every two or three years, for a total of 7 times per 19 years.

The structure, which was also used by the Israelites, was based on lunar months with the intercalation of an additional month to bring the cycle closer to the solar cycle.

That is, months reflect the lunar cycle, but then intercalary months ( e. g. " second Adar " in the Hebrew calendar ) are added to bring the calendar year into synchronisation with the solar year.

Some lunar calendars are calibrated by annual natural events which are affected by lunar cycles as well as the solar cycle.

Each carport spans 4 parking spots, provides level 1 charging ( 110 volt ) at each parking spot, and supports a 10 kW solar array.

The surface field strength of this feature is sufficient to form a mini-magnetosphere that spans 360 km at the surface, forming a 300 km thick region of enhanced plasma where the solar wind flows around the field.

* The Museum has developed a to-scale community solar system model that spans as far as the Riverside MBTA station ( in Newton, Massachusetts ).

The 10 MW plant utilizes 32, 800 SunPower solar panels, spans, and generates enough power to supply energy to approximately 1500 homes in the Midwest.

The star's effective temperature is estimated between 2930 and 3080 kelvins and radius spans between 320 and 350 solar radii ( as large as 1. 36 – 1. 5 astronomical units, roughly Mars's orbital zone ).

It has a radius of approximately 883 times that of the Sun ; if it were placed in the center of our solar system, its outer surface would lie between the orbits of Mars and Jupiter.

But in 1939, Robert Oppenheimer and others predicted that neutron stars above approximately three solar masses ( the Tolman – Oppenheimer – Volkoff limit ) would collapse into black holes for the reasons presented by Chandrasekhar, and concluded that no law of physics was likely to intervene and stop at least some stars from collapsing to black holes.

In late 2010, Caltech completed a 1. 3 MW solar array projected to produce approximately 1. 6 GWh in 2011.

If a main-sequence star is not too massive ( less than approximately 8 solar masses ), it will eventually shed enough mass to form a white dwarf having mass below the Chandrasekhar limit, which will consist of the former core of the star.

In this way, decisions made by the original designers of ephemeris time influenced the length of today's standard SI second, and in turn, this has a continuing influence on the number of leap seconds which have been needed for insertion into current broadcast time scales, to keep them approximately in step with mean solar time.

A study of 27 Milky Way neighbors found that in all dwarf galaxies, the central mass is approximately 10 million solar masses, regardless of whether the galaxy has thousands or millions of stars.

Their mass is approximately 10 < sup > 13 </ sup > solar masses.

For example, until the Tannaitic period ( approximately 10 – 220 CE ) the months were set by observation of a new crescent moon, with an additional month added every two or three years to correct for the difference between twelve lunar months and the solar year, and therefore, to keep Passover in the spring.

Because of the nonzero planetary masses and resulting perturbations, Kepler's laws apply only approximately and not exactly to the motions in the solar system.

It comes back to the position it had in relation to the solar year approximately every 33 Islamic years.

A lunar year of 12 synodic months is about 354 days, approximately 11 days short of the " 365-day " solar year.

It is a blue supergiant, at about 18 solar masses, shining with approximately 117, 000 times the luminosity of the Sun.

Studies of stratigraphic data have suggested that the solar cycles have been active for hundreds of millions of years, if not longer ; measuring varves in precambrian sedimentary rock has revealed repeating peaks in layer thickness, with a pattern repeating approximately every eleven years.

Its average value was thought to be approximately 1. 366 kW / m², varying slightly with solar activity, but recent recalibrations of the relevant satellite observations indicate a value closer to 1. 361 kW / m² is more realistic.

In stars of more than approximately 0. 5 solar mass, electron degeneracy pressure may delay helium fusion for millions or tens of millions of years ; in more massive stars, the combined weight of the helium core and the overlying layers means that such pressure is not sufficient to delay the process significantly.

Extremely massive stars ( more than approximately 40 solar masses ), which are very luminous and thus have very rapid stellar winds, lose mass so rapidly due to radiation pressure that they tend to strip off their own envelopes before they can expand to become red supergiants, and thus retain extremely high surface temperatures ( and blue-white color ) from their main sequence time onwards.

If the core of the star is not too massive ( less than approximately 1. 4 solar mass, taking into account mass loss that has occurred by this time ), it may then form a white dwarf ( possibly surrounded by a planetary nebula ) as described above for less massive stars, with the difference that the white dwarf is composed chiefly of oxygen, neon, and magnesium.

Above a certain mass ( estimated at approximately 2. 5 solar masses and whose star's progenitor was around 10 solar masses ), the core will reach the temperature ( approximately 1. 1 gigakelvins ) at which neon partially breaks down to form oxygen and helium, the latter of which immediately fuses with some of the remaining neon to form magnesium ; then oxygen fuses to form sulfur, silicon, and smaller amounts of other elements.

The production of electricity in 2009 was 20, 053TWh, which was 11 % of the solar energy the earth receives in one hour ( 174, 000TWh ).

A feature of the Islamic calendar is that a year is always 12 months, so the months are not linked with the seasons and drift each solar year by 11 to 12 days.

There were a number of such missions in the program, but the most notable were Pioneer 10 and Pioneer 11, which explored the outer planets and left the solar system.

Analysis of tree rings has revealed a detailed picture of past solar cycles: Dendrochronologically dated radiocarbon concentrations have allowed for a reconstruction of sunspot activity dating back 11, 400 years, far beyond the four centuries of available, reliable records from direct solar observation.

** Pioneer 11 is launched on a mission to study the solar system.

* November 12 – A total solar eclipse occurs over Antarctica at 14: 11: 22 UTC.

In the most massive stars ( at least 8 – 11 solar masses ), the process is continued until some of their energy is produced by fusing lighter elements to iron.

In 2002 a Japanese group propelled a tiny aluminium airplane by using a laser to vaporize a water droplet clinging to it, and in 2003 NASA researchers flew an 11 ounce ( 312 g ) model airplane with a propeller powered with solar panels illuminated by a laser.

In the new law, the age of 18 ( solar year ) would be for both genders considered and juvenile offenders will be sentenced on a separate law than of adults .” Based on the Islamic law which now seems to have been revised, girls at the age of 9 and boys at 15 of lunar year ( 11 days shorter than a solar year ) were fully responsible for their crimes.

* May 11 – Partial solar eclipse

On February 11, 1831, an annular solar eclipse was seen in Virginia.

Many, possibly most, stars have at least some variation in luminosity: the energy output of our Sun, for example, varies by about 0. 1 % over an 11 year solar cycle.

* Solar Dynamics Observatory – 11 February 2010 – Continuous solar monitoring

The delays were due both to an embargo on road works for the total solar eclipse of 11 August 1999 which saw tourists flock to Cornwall, one of the few areas of the UK in the path of totality, and also due to extremely bad weather during the winter of 1999 / 2000.

Although the date of Eid ul-Fitr is always the same in the Islamic calendar, the date in the Gregorian calendar falls approximately 11 days earlier each successive year, since the Islamic calendar is lunar and the Gregorian calendar is solar.

The Universal House of Justice has decided to celebrate them on the solar calendar, but has the authority to change the observance to the lunar calendar days, which migrate through the solar calendar by 11 or 12 days each year.