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4. Star Charting Functions
Four main types of star charts are implemented in Scientific Astronomer. They are created by the functions RadialStarChart, ZenithStarChart, CompassStarChart, and StarChart. A fifth star charting function is Planisphere.
Why Four Star Charts?
Each star charting function has its own advantages and disadvantages. For instance, StarChart works quickly because it simply draws a direct map of the ascension and declination coordinates of each star. However, this function is really only suitable for charting close to the celestial equator, as there is considerable distortion near the celestial poles. To overcome this problem, RadialStarChart can be used.
RadialStarChart can plot any part of the sky with little or no distortion in the center of the chart. Some distortion may occur on the edges if the field of view is large. This function is slower than StarChart because it has to transform the raw star positions as a function of the field of view. One feature of both StarChart and RadialStarChart is that they can zoom into small regions. They are not good at encompassing large fields of view; the two global star chart functions are more useful in this case.
ZenithStarChart and CompassStarChart can plot only large global sections of the sky. They do this in such a way as to minimize distortion as much as possible. With ZenithStarChart, the full sky above the local horizon and up to the zenith point is displayed. There is little or no distortion in the center, which is the zenith point, but around the edges and along the horizon there is some stretching. CompassStarChart takes the opposite tack and has no distortion along the horizon, but in order to do this it can display only one half of the sky above the horizon.
Setting Your Site Location
Load the package.
In[1]:=<<Astronomer`HomeSite`
This sets your location to Melbourne, Australia.
In[2]:=SetLocation[GeoLongitude -> 145.0*Degree,
GeoLatitude -> -37.8*Degree,
GeoAltitude -> 0.0*KiloMeter,
TimeZone -> 11];
Stars and Constellations
In EquatorCoordinates, HorizonCoordinates, and many other functions, you can specify a star as well as a planet, asteriod, or any other celestial object. Stars are specified using a dot notation to separate star label and constellation name, that is, star.constellation. The sky is arbitrarily divided up into a standard set of 88 constellations.
Here is a list of the 88 constellations.
In[3]:=?Constellation`*
Andromeda Cygnus Orion
Antlia Delphinus Pavo
Apus Dorado Pegasus
Aquarius Draco Perseus
Aquila Equuleus Phoenix
Ara Eridanus Pictor
Aries Fornax Pisces
Auriga Gemini PiscisAustrinus
Bootes Grus Puppis
Caelum Hercules Pyxis
Camelopardalis Horologium Reticulum
Cancer Hydra Sagitta
CanesVenatici Hydrus Sagittarius
CanisMajor Indus Scorpius
CanisMinor Lacerta Sculptor
Capricornus Leo Scutum
Carina LeoMinor Serpens
Cassiopeia Lepus Sextans
Centaurus Libra Taurus
Cepheus Lupus Telescopium
Cetus Lynx Triangulum
Chamaeleon Lyra TriangulumAustrale
Circinus Mensa Tucana
Columba Microscopium UrsaMajor
ComaBerenices Monoceros UrsaMinor
CoronaAustralis Musca Vela
CoronaBorealis Norma Virgo
Corvus Octans Volans
Crater Ophiuchus Vulpecula
Crux
Prior to 1930, there was no agreement on constellation boundaries and names-different authors often used different systems. In 1930, astronomers decided to rationalize the system and have 88 constellations and give them all Latin names. This internationally recognized system is used by Scientific Astronomer. In this system the popularly known Scorpio is referred to as Scorpius. Similarly the Big Dipper is referred to as Ursa Major, which in Latin means Great Bear.
Within each constellation, individual stars are typically labeled with Greek letters. The letter  (alpha) is usually, but not always, the brightest star in a given constellation. The convention for the full name of a star is to use the Greek letter followed by the possessive form of the constellation name. In Latin, the possessive form of Centaurus is Centauri therefore the brightest star in the constellation of Centaurus is known as (alpha) Centauri. In Scientific Astronomer, however, this star is referred to as Alpha.Centaurus-that is, the nonpossessive form of the constellation name is used and a dot is used to separate star label and constellation name. Similarly, the brightest star in Ursa Major is (alpha) Ursae Majoris, but in Scientific Astronomer it is referred to as Alpha.UrsaMajor.
Bright Star Names
The 25 brightest stars are also given special names in Scientific Astronomer. For instance, there is Sirius, which is the same as Alpha.CanisMajor; and also Polaris, which is the same as Alpha.UrsaMinor.
As normal, basic information about an object is obtained by using the ? function.
BrightStar is a Mathematica context that contains all the stars down to magnitude 1.5, but also includes Polaris at magnitude 2.02. Additionally, it includes the eclipsing variable star Algol and the wide double star Mizar.
In[4]:=?BrightStar`*
Achernar Altair Canopus Mizar Rigel
Acrux Antares Capella Polaris RigilKent
Adhara Arcturus Castor Pollux Sirius
Agena Becrux Deneb Procyon Spica
Aldebaran Bellatrix Fomalhaut Regulus Vega
Algol Betelgeuse Gacrux
Sirius is an alias for Alpha.CanisMajor or (alpha) Canis Majoris.
In[5]:=?Sirius
The SetStars Function
If you have your own list of stars, or you want to modify the current list of stars, you need to use SetStars.
Setting the stars to use in the package.
Each star in the star list should consist of a constellation name, star name, magnitude, ascension (in degrees, not hours), and declination (in degrees).
You rarely need to use this function, which simply sets a value for the list TheStars. Initially this list is set to the value of the list Stars300, but if you load <<Astronomer`Star3000`; then it is set to Stars3000.Similarly, it can be set to Stars9000.You can use the option MagnitudeRange to filter out a subset of the stars.
This loads 3,000 extra stars and automatically calls SetStars to make them available.
In[6]:=<<Astronomer`Star3000`
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