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Epoch (astronomy)
A Wisdom Archive on Epoch (astronomy)

Epoch (astronomy) A selection of articles related to Epoch (astronomy)

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Index of Articles
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Epoch Astronomy

Julian day, Julian day - Alternatives, Julian day - Calculation, Julian day - Footnotes, Julian day - History, Julian day - Julian Date, Julian day - Other Usages, Decimal time, Epoch, Epoch (astronomy), Era, Time, Time scales

ARTICLES RELATED TO Epoch (astronomy)

Epoch (astronomy): Encyclopedia II - Proper motion - Introduction

At first sight, stars seem to be in fixed positions with respect to each other, meaning they always form the same figures, and (for example) Ursa Major looks the same now as forty years ago. More careful observation shows that the constellations change shape very slowly, and that each star has an independent motion. This motion is caused by the true movement of the stars relative to the Sun and solar system through space. It is measured by two quantities: the proper motion angle and the proper motion itself. The first qu ...

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Proper motion, Proper motion - Introduction, Proper motion - History, Proper motion - Stars with high proper motion

Read more here: » Proper motion: Encyclopedia II - Proper motion - Introduction

Epoch (astronomy): Encyclopedia II - Julian day - History

The Julian day number is based on the Julian Period proposed by Joseph Scaliger in 1583, at the time of the Gregorian calendar reform, but it is the multiple of three calendar cycles used with the Julian calendar: 15 (indiction cycle) × 19 (Metonic cycle) × 28 (Solar cycle) = 7980 years Its epoch falls at the last time when all three cycles were in their first year together — Scaliger chose this beca ...

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Julian day, Julian day - Julian Date, Julian day - Alternatives, Julian day - History, Julian day - Calculation, Julian day - Other Usages, Julian day - Footnotes

Read more here: » Julian day: Encyclopedia II - Julian day - History

Epoch (astronomy): Encyclopedia II - Proper motion - History

Proper motion was discovered in 1718 by Edmund Halley, who noticed that Sirius, Arcturus and Aldebaran were over half a degree away from the positions charted by the ancient Greek astronomer Hipparchus roughly 1850 years earlier. In research published in 2005, the first measurement of the proper motion of a galaxy (the Triangulum Galaxy) was made. [1] ...

See also:

Proper motion, Proper motion - Introduction, Proper motion - History, Proper motion - Stars with high proper motion

Read more here: » Proper motion: Encyclopedia II - Proper motion - History

Epoch (astronomy): Encyclopedia II - Julian day - Calculation

The Julian day number can be calculated using the following formulas: All divisions (except for JD) are integer divisions, meaning the remainder in the division is discarded. The months January to December are 1 to 12. Astronomical year numbering is used, thus 1 BC is 0, 2 BC is −1, and 4713 BC is −4712. For a date in the Gregorian calendar (at noon): For a date in the Julian calendar (at noon): For the full Julian Date, not counting leap seconds (divisions are real numbers): So, for example, 1 January 20 ...

See also:

Julian day, Julian day - Julian Date, Julian day - Alternatives, Julian day - History, Julian day - Calculation, Julian day - Other Usages, Julian day - Footnotes

Read more here: » Julian day: Encyclopedia II - Julian day - Calculation

Epoch (astronomy): Encyclopedia II - Julian day - Julian Date

The Julian Date (JD) is the Julian day number plus the decimal fraction of the day that has elapsed since noon. Historical Julian Dates were recorded relative to GMT or Ephemeris Time, but the International Astronomical Union now recommends that Julian Dates be specified in Terrestrial Time, and that when necessary to specify Julian Dates using a different time scale, that the time scale used be indicated when required, such as JD(UT1). The fraction of the day is found by converting the number of hours, minutes, and seconds after ...

See also:

Julian day, Julian day - Julian Date, Julian day - Alternatives, Julian day - History, Julian day - Calculation, Julian day - Other Usages, Julian day - Footnotes

Read more here: » Julian day: Encyclopedia II - Julian day - Julian Date

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Index of Articles
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Epoch Astronomy