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អ្នកប្រើប្រាស់:ទួន សាម៉ន/ប្រអប់ខ្សាច់/សមភាព​រាត្រី

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ទំព័រគំរូ:Solstice-equinox


សមភាព​រាត្រី កើត​ឡើង​ពីរ​ដង​ក្នុង​មួយ​ឆ្នាំ​ប្រហែល ថ្ងៃ​ទី 20 ខែ​មីនា​ ​និង​ថ្ងៃ​ទី 22 ខែ​កញ្ញា​។ ពាក្យ​ដោយ​ខ្លួន​វា​មាន​និយមន័យ​ពាក់ព័ន្ធ​មួយ​ចំនួន​។ អត្ថន័យ​ ចាស់​ជាងគេ​គឺ​ថ្ងៃ​នៅ​ពេល​ដែល ពេល​ថ្ងៃ និង ពេល​យប់ គឺ​មាន​រយៈពេលប្រមាណ​ស្មើ​គ្នា ។ [] សមភាព​រាត្រី ពាក្យ​នេះ​បាន​មក​ពី​និយមន័យ​នេះ​ចេញ​មក​ពី ឡាតាំង aequus (ស្មើ​) និង nox (យប់​) ។ សមភាព​រាត្រី គឺ​មិន​ត្រឹមត្រូវ​ដូច​ថ្ងៃ​ដែល​រយៈ​ពេល​នៃ​ការ​ពេល​ថ្ងៃ​និង​ពេល​យប់​គឺ​ មាន​ប្រវែង​ស្មើ​គ្នា​សម្រាប់​ហេតុផល​ពីរ​។ ដំបូង​, ថ្ងៃ​រះ ដែល​ចាប់​ផ្តើ​ម​ថ្ងៃ​, កើត​ឡើង​នៅ​ពេល​កំពូល​នៃ ផ្ទៃ របស់​ព្រះអាទិត្យ​កើន​ឡើង​ខាង​លើ​ភាគ​ខាងកើត ផ្តេក ។ នៅ​ថា​ការ បន្ទាន់ , ក​ណ្តា​ល​ថា​ស​នេះ​គឺ​នៅ​តែ​មាន​នៅ​ខាង​ក្រោម​ផ្តេក​នោះ​ទេ​។ ទីពីរ​ បរិយាកាស​ផែនដី refracts ពន្លឺព្រះអាទិត្យ ។ ជា​លទ្ធផល​អ្នក​សង្កេត​ការណ៍​បាន​មើល​ឃើញ​ពន្លឺថ្ងៃ​មុន​ពេល​ឃើញ​ដំបូង​នៃ ​ថា​ស​របស់​ស៊ុន​ខាង​លើ​ផ្តេក​នោះ​ទេ​។ ដើម្បី​ជៀសវាង​ភាព​មានន័យ​មិន​ ច្បាស់លាស់​នេះ​ពាក្យ សមភាព​រាត្រី ជួនកាល​ត្រូវ​បាន​ប្រើ​ដើម្បី​មាន​ន័យ​ថា​ថ្ងៃ​ដែល​ពេល​នៃ​ការ​ពន្លឺថ្ងៃ​និង​យប់​នេះ​គឺ​ស្មើគ្នា​។ [][note ១] ពេលវេលា​នៃ​ការ ថ្ងៃលិច និង​ថ្ងៃ​រះ​ខុសគ្នា​ជាមួយ​នឹង​ទីតាំង​សង្កេត​ការណ៍​របស់ ( ត​មន​ង​ចា និង latitude ) ដូច្នេះ កាល​បរិច្ឆេទ​ពេល​ថ្ងៃ​និង​ពេល​យប់​គឺ​មាន​ប្រវែង​ស្មើ​គ្នា​យ៉ាង​ពិត​ ប្រាកដ​ក៏​អាស្រ័យ​លើ​ទីតាំង​។

ការ​និយមន័យ​ផ្សេង​ទៀត​ត្រូវ​បាន​ផ្អែក​លើ​ការ​ជា​ច្រើន​ដែល​ពាក់ព័ន្ធ ជា​បន្តបន្ទាប់ តារា​សា​ស្រ្ត ព្រឹត្តិការណ៍​និង​យោង​ទាំង​ទៅ​ព្រឹត្តិការណ៍​ខ្លួន​ឯង​ឬ​ទៅ​ថ្ងៃ​ដែល​ពួក​ គេ​បាន​កើត​មាន​ឡើង​។ ព្រឹត្តិការណ៍​ទាំង​នេះ​គឺ​ជា​មូលហេតុ​ដែល​ថា​រយៈ​ពេល ​នៃ​ការ​ពេល​ថ្ងៃ​និង​ពេល​យប់​គឺ​មាន​ចំនួន​ប្រហែល​ស្មើ​គ្នា​នៅ​ថ្ងៃ​នៃ សមភាព​រាត្រី មួយ​នេះ​។

សមភាព​រាត្រី កើត​ឡើង​នៅ​ពេល​ដែល ដំណើ​គោចរ របស់​ផែនដី តំបន់​អេ​ក្វា​ទ័ ឆ្លងកាត់​ក​ណ្តា​ល​នៃ​ព្រះអាទិត្យ​។ នៅ​ថា​ការ បន្ទាន់ ដែល​ជា ភាព​លំអៀង​នៃ​អ័ក្ស​ផែនដី មិន inclines ឆ្ងាយ​ពី​ក៏​មិន​មែន​ជា​ការ​ឆ្ពោះ​ទៅ​រក​ព្រះអាទិត្យ​។ សមភាព​រាត្រី ប្រចាំ​ឆ្នាំ​ពីរ​ដង​គឺ​មាន​តែ​នៅពេល​ដែល ចំណុច subsolar -កន្លែង​នៅ​លើ​ផ្ទៃ​ផែនដី​ជា​កន្លែង​ដែល​ក​ណ្តា​ល​នៃ​ព្រះអាទិត្យ​នេះ​គឺ​ ពិត​ជា​ចំណាយ​គឺ​នៅ​លើ​តំបន់​អេ​ក្វា​ទ័​ហើយ​ទន្ទឹម​គ្នា​នេះ​ព្រះអាទិត្យ​ គឺ​នៅ មកដល់​ចំនុច​កំពូល នៅ​លើ​ខ្សែ​អេក្វាទ័រ​។ ចំណុច subsolar នេះ​ហូរកាត់​សមីការ​នេះ​បាន​ផ្លាស់​ប្តូ​រ​ទៅ​ខាងជើង​នៅ សមភាព​រាត្រី ខែ​មីនា​និង​នៅ​ភាគ​ខាង​ត្បូង​នៅ សមភាព​រាត្រី ខែ​កញ្ញា​។ ក្នុង​អំឡុង​ពេល សមភាព​រាត្រី នោះ ផែនដី បង្គោល​ខាង​ជើង​និង​ខាង​ត្បូង​របស់​មិន​ត្រូវ​បាន tilted ឆ្ពោះ​ទៅ​រក​ឬ​នៅ​ឆ្ងាយ​ពី ព្រះអាទិត្យ និង​រយៈពេល​នៃ​ការ​ពន្លឺថ្ងៃ​គឺ​ទ្រឹ​ស្តី​ដូច​គ្នា​នៅ​គ្រប់​ចំណុច​នៅ​លើ​ ផ្ទៃ​ផែនដី​។

During an equinox, the Earth's North and South poles are not tilted toward or away from the Sun, and the duration of daylight is theoretically the same at all points on Earth's surface.

នៅ សមភាព​រាត្រី

មួយ​ព្រះអាទិត្យ​គឺ​នៅ​មួយ​ក្នុង​ចំណោម​ចំណុច​ពីរ​ផ្ទុយ​គ្នា​នៅ​លើ ដែន​សេ​ឡេ​ស្ទា​ល ដែល​ជា​កន្លែង សមីការ​សេ​ឡេ​ស្ទា​ល (ពោល​គឺ ធ្លាក់​ចុះ 0​) និង ecliptic ចំនុច​ប្រសព្វ ។ ចំណុច​ប្រសព្វ​ទាំង​នេះ​ត្រូវ​បាន​គេ​ហៅ​ថា​ចំណុច equinoctial​: Classic ចំណុច vernal នេះ ( RA = 00 ម៉ោង 00 ម៉ែត្រ 00 s និង​ត​មន​ង​ចា = 0 លេខ​) និង​ចំណុច​រដូវ​ស្លឹកឈើ​ជ្រុះ (RA = 12 ម៉ោង 00 ម៉ែត្រ 00 s និង​ត​មន​ង​ចា = 180 លេខ​) ។

សមភាព​រាត្រី នេះ​គឺ​ជា​ដង​តែ​ប៉ុណ្ណោះ​នៅ​ពេល​ដែល Terminator ព្រះ​អាទិត្យ គឺ​ជា​ការ​កាត់​កែង​ទៅ​តំបន់​អេ​ក្វា​ទ័​រ​។ ជា​លទ្ធផល​នៅ​ភាគ​ខាងជើង​និង​ ភាគ​ខាងត្បូង អឌ្ឍគោល ត្រូវ​បាន​បំភ្លឺ​ស្មើ​ភាព​គ្នា​។

សមភាព​រាត្រី នៅ​លើ​ផែនដី

[កែប្រែ]

កាលបរិច្ឆេទ

[កែប្រែ]

ពេល​ដែល Julius Caesar បាន​បង្កើត​ឡើង ប្រតិទិន​របស់​គាត់ នៅ​ក្នុង 45 ម.គ. លោក​បាន​កំណត់​ជា សមភាព​រាត្រី និ​ទា​ឃ​រដូវ 25 ខែ​មីនា​។ ដោយ​សារ​តែ​ក្នុង​មួយ​ឆ្នាំ​លោក Julian (365.25 ថ្ងៃ​) គឺ​យូរ​ជាង​មួយ​ឆ្នាំ​ពិត​ប្រាកដ​ប្រតិទិន​ឃ្លាត​ឆ្ងាយ​ដោយ​គោរព​តាម សមភាព​រាត្រី នេះ​បន្តិច​ដូច​ថា សមភាព​រាត្រី នេះ​ត្រូវ​បាន​កើតឡើង​នៅ​ប្រហែល 21 ខែ​មីនា​ក្នុង 300 គ.ស. និង​ដោយ 1500 គ.ស. វា​បាន​កើន​ឡើង​ដល់ 11 ខែ​មីនា​។

ដោយសារ​ក​ត្ដា​នេះ​ប្រាស់​ចាក​ពី ប្រកាន់ទោស​លោក Gregory XIII ដើម្បី​បង្កើត​សម័យ​ទំនើប ប្រតិទិន​គ្រី​កូ​រី ។ ប្រកាន់ទោស​ចង់​ស្ដារ​រាជបញ្ជា​ដែល​ទាក់ទង​នឹង កាល​បរិច្ឆេទ​នៃ​បុណ្យ Easter នៃ ក្រុម​ប្រឹក្សា​នៃ Nicaea នៃ 325 គ.ស. ។ (ដោយ​ចៃដន្យ​កាល​បរិច្ឆេទ​នៃ​បុណ្យ Easter ខ្លួន​វា​ត្រូវ​បាន​ជួសជុល​ដោយ​ប្រហាក់ប្រហែល​នៃ​វ​ដ្ត Lunar បាន​ប្រើ​នៅ​ក្នុង​ប្រតិទិន Hebraic មួយ​នោះ​ទេ​ប៉ុន្តែ​បើ​យោង​តាម​អ្នក​ប្រវត្តិ​សា​ស្រ្ត Bede ឈ្មោះ​ជា​ភាសា​អង់គ្លេស "បុណ្យ Easter​" មក​ពី​ការ​ប្រារព្ធ​ពិធី​ជឿ​ទៅលើ​ព្រះគ្រីស្ទ​ដោយ​កុលសម្ព័ន្ធ​អាល្លឺម៉ង់ vernal (និ​ទា​ឃ​រដូវ​) សមភាព​រាត្រី នេះ ) ។ ដូច្នេះ​ការ​ផ្លាស់​ប្តូ​រ​នៅ​ក្នុង​កាល​បរិច្ឆេទ​នៃ​ការ សមភាព​រាត្រី ដែល​បាន​កើតឡើង​រវាង​ទី 4 និង​សតវត្ស​ទី 16 ដែល​ត្រូវ​បាន​ទុក​ជា​មោឃៈ​ជាមួយ​នឹង​ប្រតិទិន​គ្រី​កូ​រី​ប៉ុន្តែ​គ្មាន​ អ្វី​ដែល​ត្រូវ​បាន​ធ្វើ​សម្រាប់​ដំបូង​បួន​សតវត្ស​នៃ​ប្រតិទិន​លោក Julian ។ ថ្ងៃ 29 ខែ​កុម្ភៈ​ឆ្នាំ​នៃ គ.ស. 100 គ.ស. 200​, 300 គ.ស. ហើយ​ថ្ងៃ​ដែល​បង្កើត​ដោយ​កម្មវិធី​មិន​ទៀងទាត់​នៃ ឆ្នាំបង្គ្រប់ រវាង​ធ្វើឃាត​របស់ Caesar និង​ក្រឹត្យ​របស់ Augustus ឡើងវិញ​រៀប​ចំ​ប្រតិទិន​នៅ​ក្នុង 8 គ.ស. នៅ​តែ​មាន​ប្រសិទ្ធិ​ភាព ។ នេះ​បាន​ផ្លាស់​ប្តូ​រ សមភាព​រាត្រី បួន​ថ្ងៃ​មុន​ជាង​នៅ​ក្នុង​ពេល​វេលា​របស់ Caesar ។

ឈ្មោះ

[កែប្រែ]
  • Vernal equinox and autumnal equinox: these classical names are direct derivatives of Latin (ver = spring and autumnus = autumn). These names are based on the seasons, and can be ambiguous since seasons of the northern hemisphere and southern hemisphere are opposites, and the vernal equinox of one hemisphere is the autumnal equinox of the other.
  • Spring equinox and fall equinox or autumn equinox: these are more colloquial names based on the seasons, and are also therefore ambiguous across hemispheres.
  • March equinox and September equinox: names referring to the times of the year when such equinoxes occur. These are without the ambiguity as to which hemisphere is the context, but are still not universal as not all people use a solar-based calendar where the equinoxes occur every year in the same month (as they do not in the Islamic calendar and Hebrew calendar, for example), and the names are not useful for other planets (Mars, for example), even though these planets do have seasons.
  • Northward equinox and southward equinox: names referring to the apparent motion of the Sun at the times of the equinox. The least culturally biased terms.
  • Vernal point and autumnal point are the points on the celestial sphere where the Sun is located on the vernal equinox and autumnal equinox respectively. Usually this terminology is fixed for the Northern hemisphere.
  • First point (or cusp) of Aries and first point of Libra are names formerly used by astronomers and now used by navigators and astrologers. Navigational ephemeris tables record the geographic position of the First Point of Aries as the reference for position of navigational stars. Due to the precession of the equinoxes, the astrological signs of the tropical zodiac where these equinoxes are located no longer correspond with the actual constellations once ascribed to them. The equinoxes are currently in the constellations of Pisces and Virgo. In sidereal astrology (notably Hindu astrology), by contrast, the first point of Aries remains aligned with Ras Hammel "the head of the ram", i.e. the Aries constellation.

ប្រវែង​នៃ​ថ្ងៃ​និង​យប់ សមភាព​រាត្រី

[កែប្រែ]
Contour plot of the hours of daylight as a function of latitude and day of the year, showing approximately 12 hours of daylight at all latitudes during the equinoxes

On the day of the equinox, the center of the Sun spends a roughly equal amount of time above and below the horizon at every location on the Earth, so night and day are about the same length. The word equinox derives from the Latin words aequus (equal) and nox (night). In reality, the day is longer than the night at an equinox. Day is usually defined as the period when sunlight reaches the ground in the absence of local obstacles. From the Earth, the Sun appears as a disc rather than a point of light, so when the center of the Sun is below the horizon, its upper edge is visible. Furthermore, the atmosphere refracts light, so even when the upper limb of the Sun is 0.4 degrees below the horizon, its rays curve over the horizon to the ground. In sunrise/sunset tables, the assumed semidiameter (apparent radius) of the Sun is 16 minutes of arc and the atmospheric refraction is assumed to be 34 minutes of arc. Their combination means that when the upper limb of Sun is on the visible horizon, its center is 50 minutes of arc below the geometric horizon, which is the intersection with the celestial sphere of a horizontal plane through the eye of the observer. These effects make the day about 14 minutes longer than the night at the Equator and longer still towards the Poles. The real equality of day and night only happens in places far enough from the Equator to have a seasonal difference in day length of at least 7 minutes, actually occurring a few days towards the winter side of each equinox.

ទិដ្ឋភាព ដែល​វាស់​ពី​ផ្ចិត​ផែនដី នៃ​រដូវ​កាល​តារា​សាស្ត្រ

[កែប្រែ]

In the half-year centered on the June solstice, the Sun rises north of east and sets north of west, which means longer days with shorter nights for the Northern Hemisphere and shorter days with longer nights for the Southern Hemisphere. In the half-year centered on the December solstice, the Sun rises south of east and sets south of west and the durations of day and night are reversed.

Also on the day of an equinox, the Sun rises everywhere on Earth (except at the Poles) at about 06:00 and sets at about 18:00 (local time). These times are not exact for several reasons:

  • The Sun is much larger in diameter than the Earth, so that more than half of the Earth could be in sunlight at any one time (due to unparallel rays creating tangent points beyond an equal-day-night line).
  • Most places on Earth use a time zone which differs from the local solar time by minutes or even hours. For example, if the Sun rises at 07:00 on the equinox, it will set 12 hours later at 19:00.
  • Even people whose time zone is equal to local solar time will not see sunrise and sunset at 06:00 and 18:00. This is due to the variable speed of the Earth in its orbit, and is described as the equation of time. It has different values for the March and September equinoxes (+8 and −8 minutes respectively).
  • Sunrise and sunset are commonly defined for the upper limb of the solar disk, rather than its center. The upper limb is already up for at least a minute before the center appears, and the upper limb likewise sets later than the center of the solar disk. Also, when the Sun is near the horizon, atmospheric refraction shifts its apparent position above its true position by a little more than its own diameter. This makes sunrise more than two minutes earlier and sunset an equal amount later. These two effects combine to make the equinox day 12 h 7 min long and the night only 11 h 53 min. Note, however, that these numbers are only true for the tropics. For moderate latitudes, the discrepancy increases (e.g., 12 minutes in London); and closer to the Poles it becomes very much larger (in terms of time). Up to about 100 km from either Pole, the Sun is up for a full 24 hours on an equinox day.
  • Night includes twilight. If dawn and dusk are instead considered daytime, the day would be almost 13 hours near the equator, and longer at higher latitudes.
  • Height of the horizon changes the day's length. For an observer atop a mountain the day is longer, while standing in a valley will shorten the day.

Day arcs of the Sun

[កែប្រែ]

Some of the statements above can be made clearer by picturing the day arc (i.e., the path the Sun tracks along the celestial dome in its diurnal movement). The pictures show this for every hour on equinox day. In addition, some 'ghost' suns are also indicated below the horizon, up to 18° below it; the Sun in such areas still causes twilight. The depictions presented below can be used for both the Northern Hemisphere and the Southern Hemisphere. The observer is understood to be sitting near the tree on the island depicted in the middle of the ocean; the green arrows give cardinal directions.

  • In the Northern Hemisphere, north is to the left, the Sun rises in the east (far arrow), culminates in the south (right arrow), while moving to the right and setting in the west (near arrow).
  • In the Southern Hemisphere, south is to the left, the Sun rises in the east (near arrow), culminates in the north (right arrow), while moving to the left and setting in the west (far arrow).

The following special cases are depicted:

សេ​ឡេ​ស្ទា​ល​សំ​រប​សំ​រួល​ប្រព័ន្ធ

[កែប្រែ]

The vernal equinox occurs in March, about when the Sun crosses the celestial equator south to north.[] The term "vernal point" is used for the time of this occurrence and for the direction in space where the Sun is seen at that time, which is the origin of some celestial coordinate systems:

Because of the precession of the Earth's axis, the position of the vernal point on the celestial sphere changes over time, and the equatorial and the ecliptic coordinate systems change accordingly. Thus when specifying celestial coordinates for an object, one has to specify at what time the vernal point and the celestial equator are taken. That reference time is called the equinox of date.[]

The autumnal equinox is at ecliptic longitude 180° and at right ascension 12h.

The upper culmination of the vernal point is considered the start of the sidereal day for the observer. The hour angle of the vernal point is, by definition, the observer's sidereal time.

The same is true in western tropical astrology: the vernal equinox is the first point (i.e. the start) of the sign of Aries. In this system, it is of no significance that the equinoxes shift over time with respect to the fixed stars.

Using the current official IAU constellation boundaries – and taking into account the variable precession speed and the rotation of the ecliptic – the equinoxes shift through the constellations as follows[] (expressed in astronomical year numbering in which the year 0 = 1 BC, −1 = 2 BC, etc.):

  • The March equinox passed from Taurus into Aries in year −1865, passed into Pisces in year −67, will pass into Aquarius in year 2597, will pass into Capricornus in year 4312. It passed along (but not into) a 'corner' of Cetus on 0°10' distance in year 1489.
  • The September equinox passed from Libra into Virgo in year −729, will pass into Leo in year 2439.

ទិដ្ឋភាព​វប្បធម៌

[កែប្រែ]

A number of traditional spring and autumn (harvest) festivals are celebrated on the date of the equinoxes.

សមភាព​រាត្រី របស់​ភព​ផ្សេង​ទៀត

[កែប្រែ]
When the planet Saturn is at equinox, its rings pick up almost no light, as seen in this image by Cassini in 2009.

Equinox is a phenomenon that can occur on any planet with a significant tilt to its rotational axis. Most dramatic of these is Saturn, where the equinox places its normally majestic ring system edge-on facing the Sun. As a result, they are visible only as a thin line when seen from Earth. When seen from above – a view seen by humans during an equinox for the first time from the Cassini space probe in 2009 – they receive very little sunshine, indeed more planetshine than light from the Sun. []

This lack of sunshine occurs once every 14.7 years. It can last a few weeks before and after the exact equinox. The most recent exact equinox for Saturn was on 11 August 2009. Its next equinox will take place on 30 April 2024.[ត្រូវការអំណះអំណាង]

One effect of equinoctial periods is the temporary disruption of communications satellites. For all geostationary satellites, there are a few days around the equinox when the sun goes directly behind the satellite relative to Earth (i.e. within the beam-width of the ground-station antenna) for a short period each day. The Sun's immense power and broad radiation spectrum overload the Earth station's reception circuits with noise and, depending on antenna size and other factors, temporarily disrupt or degrade the circuit. The duration of those effects varies but can range from a few minutes to an hour. (For a given frequency band, a larger antenna has a narrower beam-width and hence experiences shorter duration "Sun outage" windows.)[ត្រូវការអំណះអំណាង]

សូម​មើល

[កែប្រែ]

កំណត់សំគាល់

[កែប្រែ]
  1. This meaning of "equilux" is rather modern (c. 2006) and unusual; technical references since the beginning of the 20th century (c. 1910) use the terms "equilux" and "isophot" to mean "of equal illumination", in the context of curves showing how intensely lighting equipment will illuminate a surface. See for instance John William Tudor Walsh, Textbook of Illuminating Engineering (Intermediate Grade), I. Pitman, 1947.

ឯកសារ​យោង

[កែប្រែ]
  1. "equinox" at Oxford Dictionaries
  2. Owens, Steve (20 ខែមីនា 2010). "Equinox, Equilux, and Twilight Times". Dark Sky Diary (blog). Retrieved 31 ខែធ្នូ 2010.
  3. Strictly speaking, at the equinox the sun's ecliptic longitude is zero. Its latitude won't be exactly zero since the earth isn't exactly in the plane of the ecliptic. (The ecliptic is defined by the center of mass of the earth and moon combined.)
  4. Montenbruck, Oliver; Pfleger, Thomas. Astronomy on the Personal Computer. Springer-Verlag. p. 17. ល.ស.ប.អ. 0-387-57700-9. 
  5. J. Meeus; Mathematical Astronomical Morsels; ISBN 0-943396-51-4
  6. "PIA11667: The Rite of Spring". Jet Propulsion Laboratory, California Institute of Technology. Retrieved 21 ខែមីនា 2014.

តំណ​ភ្ជាប់​ខាងក្រៅ

[កែប្រែ]

ទំព័រគំរូ:Time measurement and standards ទំព័រគំរូ:Wheel of the Year