Equinox Systems GEMINI Manuel d'utilisateur télécharger pdf (Page 60)

Gemini Users Manual 55

Once the position of the selected object is calculated, additional data related to the object

can be displayed using the "Show Information" menu item. The information shown there

depends upon the catalog and object type selected. Mutual cross references,

constellation, common name, type, magnitude and size are shown for the Messier, NGC

and IC catalogs. Type and size are provided for the Sharpless 2 catalog, and

constellation, sometimes Greek letter designation, type, magnitude and spectral class are

provided for the Bright Stars. Only magnitude information is stored for SAO stars, and

double stars are marked with a "D."

5.3.2.2 Accuracy and Epochs

With the exception of the Solar System objects and the Alignment Bright Star list, all

coordinates are stored rounded to 20 arcsec, giving 10 arcsec accuracy for the standard

epoch J2000.0. The coordinates are precessed to the equinox of the date when the object

is selected; nutation is neglected. The apparent position of objects is calculated (for

standard air pressure and temperature), taking refraction into account. For the Moon,

topocentric coordinates are calculated.

By default, Gemini assumes that any input coordinates are for the epoch of the current

date. This default can be changed to Epoch J2000.0 by executing

"Setup→Communication→Coordinate Epoch→Epoch J2000.0." If this change is made

and Epoch J2000.0 coordinates are entered, Gemini will precess the entered coordinates

to the epoch of the date so that GoTo slews will be accurate. The coordinates of the

resident catalogs will not, however, be affected regardless of which epoch is selected.

5.3.2.3 Credits

In general, the whole astronomical community has to be credited with contributing to

Gemini's databases by their collecting, checking, sorting, and providing this great amount

of data. Special credits are due to Wolfgang Steinicke for long years of work checking

the NGC and IC catalogs, and correcting many bugs and errors. If there are errors in

converting his data into the internal Gemini databases, they are caused by the system's

developer.

5.3.2.4 Messier M (Messier Objects Catalog)

There are 110 Messier objects stored in this catalog, among which are nebulae, galaxies

and clusters. To select one of them, type in its Messier number from M001 to M110 and

then press the RA+ button. The object's designation, hour angle and elevation will be

displayed, indicating that it has been selected.

5.3.2.5 NGC (New General Catalog)

There are 8290 objects stored in this catalog, among which are nebulae, galaxies and

clusters. To select one of them, type in its catalog number and press the RA+ button.

The object's designation, hour angle and elevation will be displayed, indicating that it has

been selected.

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Equinox Systems GEMINI Manuel d'utilisateur Page 60