For the serious amateur, pairs with periods between 10 and 100 years are the most rewarding in terms of being able to follow them over a significant portion of their apparent orbit. A good example of a pair in this category is Z Her with a period of 34.385 years. The apparent separation ranges from 0.5'' to 1.5'', but because the pair is unequally bright (2.8 magnitudes in V) when it is near periastron, to see it requires at least a 30-cm aperture. It should be noted that many of these pairs are grade 1 although it is almost certain that Hipparcos will have added pairs in this region of which very few observations have ever been made from the ground and which would benefit from further coverage. These are likely to be difficult visually, however. All of the Hipparcos discoveries can be found in the WDS catalogue on the CD-ROM. The discovery code is HDS whilst TDS and TDT indicate additional pairs found by the satellite from the Tycho project.
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