8.5 The NGC and IC Functions
You can access the New General Catalog, Index Catalog, and Messier's catalog of nonstellar objects using Scientific Astronomer.
The New General Catalog is a large list of nonstellar objects including galaxies, nebulae, and clusters. The Index Catalog is a supplement to the New General Catalog. Messier's catalog is a small, but popular, list of objects compiled by Charles Messier in the 18th century.
To access the New General Catalog or Index Catalog, you can use the NGC and IC functions. Only a small number of catalog objects are built into Scientific Astronomer, but to access a more extensive list, you can load the DeepSky.m package.
Accessing deep sky catalogs.
NGC, IC, and M return a set of rules that you can use as an object. Specifically, the functions return the right ascension, declination, distance, apparent magnitude, apparent diameter, appearance type, and catalog alias of an index item in the catalog. The appearance type is either a galaxy, diffuse nebula, planetary nebula, open cluster, or globular cluster.
As an example, M returns information about M45, or the Pleiades star cluster. Similarly, NGC returns details about the M31 Andromeda Galaxy, also known as NGC 224.
This loads a file containing many deep sky objects.
Information about NGC 224 is given here.
IC 2621 is a planetary nebula located in the southern skies with declination -65 degrees. It has an apparent magnitude of 10.5.
The catalogs are typically accessed using the index number of the object you want information on. However, as noted in Chapter 2, many objects of interest to amateur astronomers have names defined in Scientific Astronomer. You can also access the catalogs using these names, rather than the index numbers.
Here is the catalog entry for the Orion Nebula, the brightest nebula in the sky.
The catalog entry for the well-known Andromeda Galaxy shows that it is 2.2 million light years from Earth.