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    Eclipse maps & solar semidiameter
    From: Paul Hirose
    Date: 2017 Aug 15, 14:46 -0700

    An article in the Kansas City Star warns that the edge of totality,
    depicted with great precision on eclipse maps, should not be taken as
    the literal truth. One uncertainty is the Sun's semidiameter. There is a
    feeling among some astronomers that the Sun is a little bigger than its
    official IAU radius of 696,000 km.
    "Anyone who has been using online maps to decide where they intend to
    view the historic Aug. 21 total eclipse of the sun may want to take
    another look.
    "Those maps, provided by NASA and others, show a crisply defined,
    70-mile-wide path of totality where the moon will block 100 percent of
    the sun. But they are not as precise as they appear, at least on their
    "Xavier Jubier, a French engineer whose calculations have been used to
    create the interactive Google maps of the eclipse, confirmed to The Star
    by email that the actual path of the totality is slightly narrower than
    the 70 miles shown on current maps.
    "Jubier said that the current maps are accurate using the
    696,000-kilometer radius and other standards agreed upon in 1976 at a
    meeting of the International Astronomical Union.
    "'This is perfectly accurate but we know it does use a solar diameter
    that is not large enough. Why don’t we change the value(?)' Jubier
    wrote. 'Well simply because the IAU (International Astronomical Union)
    has not yet approved a new value. This is part of the research we’re
    doing and for which we’re looking for funding.'
    "He continued, 'So technically speaking if the Sun is larger than the
    adopted IAU value, and we know it is, the eclipse path is necessarily
    narrower and our tools can simulate this, yet the standard maps for the
    public will still retain the currently adopted solar radius until a new
    value has been accepted. Such a process will take years as everything
    needs to be peer-reviewed and then validated during a General Assembly.'"
    In practice I don't think this will be an issue, since anyone near the
    edge will naturally move toward the central line in order to get a
    longer totality.

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