Rare?

You want RARE?

How about a transit of both mercury and venus "across" the sun at the same
time...

But ALSO....

Its during a nearly perfect barely ANNULAR/TOTAL solar eclispe (the rarest of
em..... a small fraction of the solar eclipse family)....in other words the
moon is neither too big or too small but instead just the right size...

Mecury and Venus both pass directly across the apparent center (or very near)
of the suns disk from as viewed from somewhere on earth....

AND

Both Mercury and Venus cross the "center" of the sun at the same time....

.....or in other words Venus "eclipses" both Mercury and the Sun as Mercury is
transiting the Sun and the Moon is eclipsing ALL three of em.....

And heck....throw in a centered ISS transit just for good measure

take care

Blll