star.phases: Calculate the seasons and phase type of a star
In skyscapeR: Data Analysis and Visualization for Skyscape Archaeology

Description Usage Arguments References See Also Examples

This function calculates the seasons (Rising, Setting, etc.) and phase types (Arising and Lying Hidden, Curtailed Passage) of a star for a given location and epoch. This functions uses the arcus visionis approximation of Purrington (1988) and the atmospheric extinction approximation of Schaefer (1989). For the nomenclature used, and description of star phase types, see Brady (2015).

star.phases(
  star,
  year,
  loc,
  alt.hor = 0,
  k = 0.2,
  limit = 6,
  alt.rs = 10,
  res = 1/24/6,
  refraction,
  atm,
  temp
)

`star`	Either the star name or a skyscapeR.star object.
`year`	The year of interest. Must be in the swephR range of 13201 cal BC to 17191 AD
`loc`	Location, either a skyscapeR.object or a vector containing the latitude and longitude of location, in this order.
`alt.hor`	(Optional) The altitude of the horizon to consider. Defaults to zero degrees.
`k`	(Optional) Extinction coefficient (see Schaefer 1989). Defaults to 0.2, corresponding to a poor night on mountain top or best night at a dry sea level site.
`limit`	(Optional) The maximum magnitude of a star that can be visible with the naked eye. Defaults to 6.
`alt.rs`	(Optional) The maximum altitude of a star's first or last visibility for it to still be considered to be as rising or setting. Defaults to ten degrees.
`res`	(Optional) Resolution of calculation. The smaller this figure the slower the computation. Defaults to 1/24/6, i.e. every 10 minutes.
`refraction`	(Optional) Whether atmospheric refraction is to be taken into account. If not given the value set by `skyscapeR.vars` will be used instead.
`atm`	(Optional) Atmospheric pressure for refraction calculation. If not given the value set by `skyscapeR.vars` will be used instead.
`temp`	(Optional) Atmospheric temperature for refraction calculation. If not given the value set by `skyscapeR.vars` will be used instead.

Purrington, Robert D. (1988) Heliacal Rising and Setting: Quantitative Aspects, Journal for the History of Astronomy (Archaeoastronomy Supplement 12) 19, S72-S84. Available online at [SAO/NASA ADS Astronomy Abstract Service](http://adsabs.harvard.edu/abs/1988JHAS...19...72P)

Brady, Bernadette (2015) Star Phases: the Naked-eye Astronomy of the Old Kingdom Pyramid Texts. In F Silva and N Campion (eds) Skyscapes: The Role and Importance of the Sky in Archaeology. Oxford: Oxbow Books, pp. 76-86.

plot.skyscapeR.starphases

## Not run: 
ss1 <- star.phases('Aldebaran',-4000, c(35,-8,200))

# One can then look at the star's phase type:
ss1$metadata$type

# Date range of seasons:
ss1$metadata$seasons

# Date range of phase-type events:
ss1$metadata$events

# And plot them:
plot(ss1)

# You can play with the parameters and see how predictions change:
ss1 <- star.phases('Aldebaran',-4000, c(35,-8,200), alt.hor=2, alt.rs=5)
plot(ss1)

## End(Not run)