The aim of the Merge Star Database project is to create a realistic map of our neck of the Milky Way galaxy — not only for the 3D placement of stars, but also for pegging the position of each star in its lifetime. With these and other derived data, it might be possible to plot the locations of systems likely to contain mature, habitable worlds. Even if we don't yet have the technology to sail that broad, dark ocean between stars, knowing which suns likely shine down on other Earths, makes the dream of star travel that much more vividly alive.

Thousands of articles have been consulted in order to refine and clarify the data of individual stars and multiple systems. The literature is filled with thousands of inconsistencies in the data, and many more instances of missing data. Also, numerous anomalies in the data point either to the existence of as yet undiscovered members of existing systems, or the existence of stellar types and processes not yet defined or understood. Likely, all of this apparent confusion in the data derives more from the difficulty of observation and subtle changes in data, than from human error. Also, differences in interpretation sometimes greatly alter the judgments placed on the data.

Part of the challenge for the MSDB project has been filling in the missing pieces and finding plausible compromises to conflicting data. In some instances, data has been fabricated rather than leave records blank. These additions act as placeholders for later refinement and update. For this and other reasons, scientific use of this data is not recommended.

Some of astronomy's most pressing questions can seem tantalizingly simple, but the answers equally elusive. For example, a single star might appear uncharacteristically bright. It may be listed in the literature with a fairly reliable distance from trigonometric parallax and a well-defined spectral type and luminosity class. Compared to single stars with similar spectra, its brightness might demand a reassessment of the published distance. On the other hand, it might be that the distance is accurate enough, but that an undiscovered companion is contributing the additional light.

One widely used technique for detecting companion stars depends on periodic changes in radial velocity of a star and its companion. "Radial velocity" is merely that portion of a star's motion which is directed toward or away from Earth. Refinements in this technique have led to the discoveries of many of the extrasolar planets now known to exist. Astronomers derive these changes from the spectra of one or more stars in a binary or multiple system as they orbit one another. If however the plane of the orbits is close to perpendicular to the line of sight, such periodic shifts in the spectra never make it to Earth.

The duplicity of still other systems has been cast into doubt. Such shifts in spectra, at times, can be caused by pulsations in the outer atmosphere of a single star, and not necessarily by the orbits of two stars.

Numerous visual double stars have been found not to be physically related, though some sources still list them together. The stars are paired by a mere chance alignment and may actually be separated by distances far too great to allow for physical interaction. Still other double or multiple systems have not yet changed sufficiently in the decades, or even centuries, since discovery to yield a verdict on their true relationship. More study, and perhaps more time, are required to settle these questions.

One possibility for great improvements in the data could be achieved by having the next Voyager-like probe double as a platform for wide-baseline trigonometric studies of stars at high angles to the probe's path. Such a study could greatly increase the accuracy of the published distances to Solar vicinity stars. Also, the relationship of members of published double and multiple systems might more readily be found to be mere visual alignment rather than one of a physical connection.

The volume of space contained by the Solar vicinity is, without argument, immense. As defined in the software, the vicinity (a cube 192 parsecs on a side) might contain nearly half a million stars. Most of these are missing from the MSDB, and from the software, simply because we don't know which ones they are. Of the millions of dim stars already cataloged elsewhere, only a comparative handful have been listed with spectral types and luminosity classes. Most are far too remote for reasonably accurate trigonometric distances. Tens of thousands of red dwarfs at the outskirts of the vicinity are thus lost amongst millions of brighter, but far more remote giants and subgiants. From Earth, many of these glowing embers are at a visual magnitude of 20 or dimmer — nearly 400,000 times fainter than the edge of naked-eye visibility. Deciphering which stars belong to the Solar vicinity may prove to be an impossible task with the currently available data.

Through continued research of the literature and the analysis of additional catalogs of stellar data, it is hoped that the Merge Star Database will continue to grow in the accuracy of its portrayal of the Solar neighborhood and vicinity.