Thus, if every historian were to claim that there was a solar eclipse in the year 1600, then though we might at first naively regard that as in violation of natural laws, we'd come to accept it as a fact.

In the case of an observer on Earth, the direction of a star's velocity varies during the year as Earth revolves around the Sun ( or strictly speaking, the barycenter of the solar system ), and this in turn causes the apparent position of the star to vary.

The length of the interval between two such successive events may be allowed to vary slightly during the year, or it may be averaged into a mean solar day.

Not all calendars use the solar year as a unit.

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.

Because the number of days in the tropical year is not a whole number, a solar calendar must have a different number of days in different years.

Even if a calendar is solar, but not lunar, the year cannot be divided entirely into months that never vary in length.

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 solar year of the Taichu calendar was defined as days and the lunar month as days.

Smoothed historical measurements of ΔT using total solar eclipses are about + 16800 s at the year − 500 ( 501 BC ), + 10600 s at 0 ( 1 BC ), + 5700 s at 500 ( AD ), + 1600 s at 1000, and + 180 s at 1500.

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.

In each solar year ( 1 January to 31 December inclusive ), the lunar month beginning with an ecclesiastical new moon falling in the 29-day period from 8 March to 5 April inclusive is designated as the paschal lunar month for that year.

In addition, without changes to either calendar, the frequency of monthly divergence between the two festivals will increase over time as a result of the differences in the implicit solar years: the implicit mean solar year of the Hebrew calendar is 365. 2468 days while that of the Gregorian calendar is 365. 2425 days.

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.

Following this, an astronomical conference held in Paris in 1950 recommended " that in all cases where the mean solar second is unsatisfactory as a unit of time by reason of its variability, the unit adopted should be the sidereal year at 1900. 0, that the time reckoned in this unit be designated ephemeris time ", and gave Clemence's formula ( see Definition of ephemeris time ( 1952 )) for translating mean solar time to ephemeris time.

The five or six extra days needed to approximate the solar or tropical year were placed after the months at the end of each year.

On October 20 of the same year, English astronomer Norman Lockyer observed a yellow line in the solar spectrum, which he named the D < sub > 3 </ sub > Fraunhofer line because it was near the known D < sub > 1 </ sub > and D < sub > 2 </ sub > lines of sodium.

Omar Khayyám ( 1048 – 1131 ), a Persian scientist, calculated the length of a solar year to 10 decimal places and was only out by a fraction of a second when compared to our modern day calculations.

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.

`` The human ego being what it is '', I put in, `` science fiction has always assumed that the creatures on the planets of a thousand larger solar systems than ours must look like gigantic tube-nosed fruit bats.

The infrared emission could then be assumed to originate at the surface of the moon, while the radio emission originates at some depth beneath the surface, where the temperature variation due to solar radiation is reduced in amplitude and shifted in phase.

The radio radiation of the sun which is reflected from the moon and planets should be negligible compared with their thermal emission at centimeter wave lengths, except possibly at times of exceptional outbursts of solar radio noise.

Therefore, neglecting the extreme outbursts, reflected solar radiation is not expected to cause sizable errors in the measurements of planetary radiation in the centimeter- and decimeter-wave-length range.

Wyatt and Whipple, 1950 ), which is a retardation of the orbital motion of particles by the relativistic aberration of the repulsive force of the impinging solar radiation, causes the dust to spiral into the sun in times much shorter than the age of the Earth.

The radius is calculated from the mass by assuming spheres of density Af except for the smallest particles, which must have a higher mass density to remain in the solar system in the presence of solar-radiation pressure.

`` The planet is very low in radiation from mineral deposits, and the atmosphere seems to shield out most of the solar output.

In a passive solar home, this is called a Trombe wall.

Amateur astronomy is usually associated with viewing the night sky when most celestial objects and events are visible, but sometimes amateur astronomers also operate during the day for events such as sunspots and solar eclipses.

Argon is notable in that its isotopic composition varies greatly between different locations in the solar system.

An alternative is the Seawater Greenhouse which desalinates water through evaporation and condensation using solar energy as the only energy input.

* 1831 – Nat Turner sees a solar eclipse, which he believes is a sign from God.

Astrometry is responsible for the detection of many record-breaking solar system objects.

With the definitions used before 2012, the astronomical unit was dependent on the heliocentric gravitational constant, that is the product of the gravitational constant G and the solar mass M < sub >☉</ sub >.

Some parts at least of the figure above mentioned are solar symbols, and the Basilidian Abrasax is manifestly connected with the sun.

Note electrode naming for diodes is always based on the direction of the forward current ( that of the arrow, in which the current flows " most easily "), even for types such as Zener diodes or solar cells where the current of interest is the reverse current.

The flow of electrons is always from anode to cathode outside of the cell or device, regardless of the cell or device type and operating mode, with the exception of diodes, where electrode naming always assumes current in the forward direction ( that of the arrow symbol ), i. e., electrons flow in the opposite direction, even when the diode reverse-conducts either by accident ( breakdown of a normal diode ) or by design ( breakdown of a Zener diode, photo-current of a photodiode or solar cell ).

Polybius tells that 28 years after the expulsion of the last Persian king Xerxes crossed over to Greece, and that event is fixed to 478 BC by two solar eclipses.

Also, hydrogenated amorphous silicon, a-Si: H in short, is of technical significance for thin film solar cells.

Power, including electricity, heat and water heating, is from solar power.

The largest advantage of wind power is that larger wind turbines have a lower per-watt cost than solar cells, provided there is wind.

The basic requirement for passive solar heating is that the solar collectors must face the prevailing sunlight ( south in the northern hemisphere, north in the southern hemisphere ), and the building must incorporate thermal mass to keep it warm in the night.