Moon

Accessor to all values underlying the geocentric physical details. Will probably become private once all relevant accessors are implemented and covered.

Accessor to all values underlying the selenographic details. Will probably become private once all relevant accessors are implemented and covered.

Accessor to all values underlying the eclipse details. Will probably become private once all relevant accessors are implemented and covered.

The diameter of the Moon.

The standard/mean apparent altitude for rise and set of the Moon. See AA p.102.

Radius vector of the Moon, that is, its distance from Earth (not Sun). AA+ uses the Eq. for Delta written in p.342 of AA book. According to that Eq., the result is in Kilometers. For consistency with others, we return AU.

Convenience accessor of the Moon distance, that is, its distance from Earth (not Sun), in kilometers.

Horizontal parallax

The apparent ecliptic coordinates of the Moon. In AA p.342, Example 47.a, they are called geocentric longitude and latitude. But apparent right ascension and declination are derived directly from them using standard coordinates transformations. These coordinates are ‘apparent’ coordinates because they include the effect of nutation in longitude. It is important to provide the current julian day as epoch to get the right coordinates.

The apparent equatorial coordinates of the Moon, obtained from the apparentEclipticCoordinates.

The ecliptic coordinates of the Moon. [WARN]: For now, return the apparent ones. TODO: Is there any other coordinates one could find? Is it meaningful?

The equatorial coordinates of the Moon. [WARN]: For now, return the apparent ones. TODO: Is there any other coordinates one could find? Is it meaningful?

This is the geocentric semi diameter of the moon, that is for an observer located at the center of the Earth

This is the topocentric semi diameter of the moon, that is for an observer located somewhere on the surface of the Earth.

The mean longitude of the Moon

The mean elongation of the Moon

The mean anomaly of the moon

The argument of Latitude

The longitude of mean perigee

The longitude of the mean ascending node

The longitude of the true ascending node.

Returns the Julian Day of the Moon phase.

Computes the optical librations of the Moon. That is the displacement, at any time, of the mean center of the disk from the apparent center, measured by the selenographic coordinates of the apparent center of the disk at that time. Optical librations are due to variations of the geometric position of the Earth relative to the lunar surface during the course of the orbital motion of the Moon.

Computes the physical librations of the Moon, which is due to the actual rotational motion of the Moon about its mean rotation. This is much smaller than the optical libration.

Computes the total librations of the Moon, which is the sum of the optical and physical librations.

AA (p.375): For precise reduction sof observations, the geocentric values of the librations and position angle of the axis should be reduced to the values at the place of the observer on the surface of the Earth. For the librations, the differences may reach 1 degree and have important effects on the limb-contour.

The position angle of the Moon’s axis of rotation

AA (p.376): The selenographic coordinates of the Sun determine the regions of the lunar surface that are illuminated. The coordinates returned are those of the subsolar point, that is, the point on the Moon surface where the Sun is in the zenith.

Computes the altitude of the Sun above the Moon’s horizon on a given location in the Moon surface.

Computes the time of the sunrise, for a given location in the Moon surface, taking the center of the Sun apparent disk.

Computes the time of the sunset, for a given location in the Moon surface, taking the center of the Sun apparent disk.

Computes the date of the perigee.

Computes the date of the apogeee.

Computes the parallax of the perigee

Computes the parallax of the apogeee

Compute the date of the maximum declination of the Moon.

Computation are geocentric, and they refer to the center of the Moon’s disk.

The plan of the Moon’s orbit forms with the plane of ecliptic an angle of 5º. Therefore, in the sky the Moon is moving approximatively along the ecliptic, and during each revolution (27 days) it reaches its greatest northern declination (in Tauris, Gemini or in northern Orion), and two weeks later its greatest southern declination (in Sagittarius or in Ophiuchus).

Because the lunar orbit forms with the ecliptic an angle of 5º, and the ecliptic an angle of 23º with the celestial equator, the extreme declinations of the Moon are between 18º and 28º (North or South), approximately. When, as in 1987, the ascending node of the lunar orbit is in the vicinity of the the vernal equinox, the Moon reaches high northern and southern declinations, approximately +28.5º and -28.5º. This situation is repeated at intervals of 18.6 years, the revolution period of the lunar nodes.

Note that the word ‘mean’ is opposed to ‘true’ in the sense that the former takes into accounnt the abberration and light-time effects. Since the word ‘true’ is a reserved word in the Swift programmatic language, the parameter name must be different, hence the choice of the word ‘mean’.

Compute the value of the maximum declination of the Moon

Compute the geocentric elongation of the Moon

The phase angle of the Moon

The illuminated fraction of the Moon

The position angle of the Moon’s bright limb is the position angle of the midpoint of the illuminated limb of the Moon, reckoned eastward from the North Point of the disk (not from the axis of rotation of the lunar globe).

Computes the date of the passage of the Moon through the ascending node.

Computes the date of the passage of the Moon through the descending node.