Our need, as binocular users, for sky charts, is no less than the need of telescopic astronomers, but is slightly different. Unless we are using giant binocular telescopes, we do not need charts that go as deep as those preferred by users of large telescopes. This means that our needs are usually completely met by the better "paper" charts and by most of the commonly available star-charting software. For example, the excellent Sky Atlas 2000 goes down to magnitude 8.5 and incorporates galaxies and nebulae that are fainter than this. The choice of charts is therefore a matter of preference and, often, familiarity.
If our choice to use binoculars is based to some extent on their extreme portability, we may wish to use charts or software that incorporate the same philosophy of choice. If this is the case, there is one paper chart that stands out: Collins Gem Stars (some older editions were called Collins Gem Night Sky). This little book is small enough to fit into a shirt pocket and contains sufficient information to keep the users of small and medium binoculars amused for many nights.
If you prefer to use charting software, the "extremely portable" route suggests using a hand-held computer or personal digital assistant (PDA). There are a number of excellent software options for these, depending on the operating system used by the hand-held viewer. In general, there is more astronomical software written for PalmOS than for other operating systems.
Of the many examples of astronomical software available for PDAs, there are three planetarium programs that stand out:
• 2Sky: This is commercial software and is not offered as an evaluation version, but has a 30-day refund policy if you find the software to be unsuitable. The "basic" version ($25) has stars to magnitude 7 and 500 deep sky objects (DSOs), the "total" version includes stars down to magnitude 9.5 and 13,600 DSOs from the Messier/NGC/IC catalog, and the "mega" version has stars to magnitude 11.2 and the same DSOs as the "total"version. It also comes with 2Red, which changes the entire PDA to red-screen night mode.
• Planetarium: This is "nagware," that is, shareware that, until you register it, reminds you when you start and/or close the program that it is unregistered. It costs $24 to register. This is my most-used astronomical software. It has a "Compass View" that shows the lunar phase and, at a quick glance, the altitude and azimuth of the Sun, Moon, major planets, and one other object of your choice. It has instantly accessible rise and set tables and twilight tables. Among its most useful features is the ease with which catalogs of your choosing can be added to its database and with which objects can be imported into a "Personal" catalog that can be exchanged with other Planetarium users. It has stars to magnitude 6.5 as standard, but there are databases that go, by increments of one magnitude, down to 11.5 (i.e., the entire Tycho2/Hipparchos catalog).
• PleiadAtlas: Like Planetarium, this is nagware ($10 to register). It goes down to magnitude 11.5 and incorporates the Messier, NGC, and IC catalogs.
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