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PlanetChart, EclipticChartSunRise, SunSet, NewMoon, FullMoon

2.3 The Planisphere Function

Planisphere produces either two or four graphic plates that you can use to build a planisphere for a given geographic latitude. A planisphere is a device for determining which stars are above the local horizon at any given hour for each day of the year.

Producing planispheric plates.

To construct the two-plate planisphere, print the first plate onto cardboard and the second plate onto a transparency. Then rivet the plates together at the center, which is marked with a small red circle. Trim the plates to the outer circle. You may also want to glue a graphic generated by OuterPlanetChart to the back of the planisphere. The OuterPlanetChart function is discussed in Section 5.5.

A two-plate planisphere is suitable for use in latitudes greater than 30 degrees north or south of the equator. There is, additionally, a four-plate planisphere suitable for latitudes less than 45 degrees north or south. If your latitude is between 30 and 45 degrees north or south, you can use either of the two styles. To generate the four-plate planisphere, use the option setting Fold -> True. Construction of the four-plate planisphere is similar to the two-plate planisphere except that the second set of two plates goes on the back of the first set of two plates, and there is no need to use the OuterPlanetChart graphic. The four-plate planisphere produces a more detailed and accurate representation of the sky than the two-plate planisphere. It is, however, more difficult to construct, as additional gluing and cutting is required.

This displays the two planisphere plates needed for latitude -38 degrees in the southern hemisphere. By default, stars with magnitude less than 3.5 are not displayed, but you can changed this using the option MagnitudeRange.

In[16]:=Planisphere[GeoLatitude -> -38*Degree,
StarLabels -> True,
RotateLabel -> False];

To align the planisphere, hold it above your head and orient the North and South points to the corresponding true compass directions. The red circle, where the rivet is located, will point to your celestial pole, which is either north or south depending on your hemisphere. The cross in the middle of the second plate will represent the zenith point directly above your head, and the gray lines are 30 degrees apart.

To use the planisphere, keep the front plate stationary, and rotate the back plate with the stars on it, so that the month and day point to the desired hour on the front plate. Stars that are visible through the window in the front plate are the stars that are visible in the real sky at that time. Standard time is represented in the outer circle of hours and daylight-saving time in the inner circle.

On the back plate, the blue ring represents the ecliptic line along which all the planets and Moon approximately move. To find a planet you can either scan along that line in the real sky to find an unfamiliar object, or you can use OuterPlanetChart to create a finder chart. The finder chart is designed to be glued to the very back of the planisphere for easy reference. Another way to locate planets in the sky is to remember that planets do not twinkle, unlike stars, which do twinkle as a rule.

Labeled on the outer rim of the planisphere are the right ascension hour and the zodiac constellations.

Any of the options available to StarChart are available to Planisphere. However, MagnitudeRange -> {-Infinity, 3.5} is used by default in order to keep the star plate from becoming too cluttered.

PlanetChart, EclipticChartSunRise, SunSet, NewMoon, FullMoon