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Updates: Tycho-2 database

The Distant Worlds Star Mapper can now use the Tycho-2 catalog for many of its charts. Prepared from the same mission that created the Hipparcos catalog, the Tycho-2 catalog has almost 20 times as many stars as the Hipparcos catalog -- over 2.5 million, including 99% of all stars to magnitude +11, and 90% to magnitude +11.5. Since the core of the Mapper's database was originally the Hipparcos catalog, there is clearly a huge difference. Here are some examples:

M6 + M7, old catalog (to about magnitude +8.5 with occasional fainter stars):

M6 + M7, Tycho-2 version (here limited to magnitude 10, so this is still only a fraction of the stars it can show):

Additional samples after the break.

Beehive (M44), old catalog:

Beehive (M44), Tycho-2:

M35, old catalog:

M35, Tycho-2:

Be aware that with 20x as many stars, there are a few tradeoffs. In particular:

  • The Tycho-2 dataset has no distance (parallax) information. As a result, all Tycho-2 maps ignore the "View From Location" settings. Your "view from" location will always be the Sun.
  • For the same reasons, the Tycho-2 dataset can't handle 3-D space motions, so any map you make with a "Years before/after epoch" setting will use 2-D motions only. These are, of course, much less accurate over long times.
  • The Tycho-2 dataset only appears at magnifications of 4 and up.
  • To prevent too many stars from appearing, the magnitude limit is throttled at each magnification level. The maximum magnitude is +8.0 at base magnification (1) and goes up by +0.4 for each unit of magnification. Thus, to see stars with magnitude +10.0, you need a magnification of at least 6.
  • Tycho-2 maps are much slower to create than Hipparcos maps. Please be patient.

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