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Reworking Python body codes as enumerated type Body.
This will help documentation generator pydown.py organize body codes and other similar enumerations together as classes.
This commit is contained in:
Don Cross
@@ -1,143 +0,0 @@
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# astronomy
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Astronomy Engine by Don Cross
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See the GitHub project page for full documentation, examples,
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and other information:
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https://github.com/cosinekitty/astronomy
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## BodyCode
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```python
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BodyCode(name)
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```
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Finds the integer body code given the name of a body.
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Parameters
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----------
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name: str
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The common English name of a supported celestial body.
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Returns
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-------
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int
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If `name` is a valid body name, returns the integer value
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of the body code associated with that body.
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Otherwise, returns `BODY_INVALID`.
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Example
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-------
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>>> astronomy.BodyCode('Mars')
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3
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## Time
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```python
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Time(self, ut)
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```
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Represents a date and time used for performing astronomy calculations.
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All calculations performed by Astronomy Engine are based on
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dates and times represented by `Time` objects.
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Parameters
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----------
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ut : float
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UT1/UTC number of days since noon on January 1, 2000.
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See the `ut` attribute of this class for more details.
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Attributes
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----------
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ut : float
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The floating point number of days of Universal Time since noon UTC January 1, 2000.
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Astronomy Engine approximates UTC and UT1 as being the same thing, although they are
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not exactly equivalent; UTC and UT1 can disagree by up to 0.9 seconds.
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This approximation is sufficient for the accuracy requirements of Astronomy Engine.
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Universal Time Coordinate (UTC) is the international standard for legal and civil
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timekeeping and replaces the older Greenwich Mean Time (GMT) standard.
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UTC is kept in sync with unpredictable observed changes in the Earth's rotation
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by occasionally adding leap seconds as needed.
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UT1 is an idealized time scale based on observed rotation of the Earth, which
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gradually slows down in an unpredictable way over time, due to tidal drag by the Moon and Sun,
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large scale weather events like hurricanes, and internal seismic and convection effects.
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Conceptually, UT1 drifts from atomic time continuously and erratically, whereas UTC
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is adjusted by a scheduled whole number of leap seconds as needed.
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The value in `ut` is appropriate for any calculation involving the Earth's rotation,
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such as calculating rise/set times, culumination, and anything involving apparent
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sidereal time.
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Before the era of atomic timekeeping, days based on the Earth's rotation
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were often known as <i>mean solar days</i>.
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tt : float
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Terrestrial Time days since noon on January 1, 2000.
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Terrestrial Time is an atomic time scale defined as a number of days since noon on January 1, 2000.
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In this system, days are not based on Earth rotations, but instead by
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the number of elapsed [SI seconds](https://physics.nist.gov/cuu/Units/second.html)
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divided by 86400. Unlike `ut`, `tt` increases uniformly without adjustments
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for changes in the Earth's rotation.
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The value in `tt` is used for calculations of movements not involving the Earth's rotation,
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such as the orbits of planets around the Sun, or the Moon around the Earth.
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Historically, Terrestrial Time has also been known by the term <i>Ephemeris Time</i> (ET).
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### Make
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```python
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Time.Make(year, month, day, hour, minute, second)
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```
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Creates a `Time` object from a UTC calendar date and time.
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Parameters
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----------
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year : int
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The UTC 4-digit year value, e.g. 2019.
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month : int
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The UTC month in the range 1..12.
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day : int
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The UTC day of the month, in the range 1..31.
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hour : int
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The UTC hour, in the range 0..23.
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minute : int
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The UTC minute, in the range 0..59.
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second : float
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The real-valued UTC second, in the range [0, 60).
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Returns
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-------
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Time
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## Observer
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```python
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Observer(self, latitude, longitude, height=0)
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```
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Represents the geographic location of an observer on the surface of the Earth.
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:param latitude: Geographic latitude in degrees north of the equator.
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:param longitude: Geographic longitude in degrees east of the prime meridian at Greenwich, England.
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:param height: Elevation above sea level in meters.
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## GeoMoon
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```python
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GeoMoon(time)
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```
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Calculates the geocentric position of the Moon at a given time.
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Given a time of observation, calculates the Moon's position as a vector.
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The vector gives the location of the Moon's center relative to the Earth's center
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with x-, y-, and z-components measured in astronomical units.
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This algorithm is based on Nautical Almanac Office's <i>Improved Lunar Ephemeris</i> of 1954,
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which in turn derives from E. W. Brown's lunar theories from the early twentieth century.
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It is adapted from Turbo Pascal code from the book
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[Astronomy on the Personal Computer](https://www.springer.com/us/book/9783540672210)
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by Montenbruck and Pfleger.
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Parameters
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----------
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time : Time
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The date and time for which to calculate the Moon's position.
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Returns
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-------
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Vector
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The Moon's position as a vector in J2000 Cartesian equatorial coordinates.
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