a) To Shekhar's question, the cluster from which our Sun came is long since
dispersed, and we have no way from motions nor mechanics to discern from
what part of the galactic neighborhood it came, nor what other stars were
part of the original cluster. No such thing as a 5 billion-year old open
cluster.
b) Dickinson's Nightwatch had the other answers. We got this book by
accident, when ASP sent it instead of Norton's, and it was serendipitous. I
was _not_ an astro illiterate when I read it last year, and about 20% of
the stuff in the book was new to me. Flat gorgeous layout.
Here, on p 25, he starts, "Our Sun and planetary system seem to be just
entering the Orion Arm. Many of the stars in our immediate vicinity are
members of a pocket of fairly young stars called Gould's Belt, inside the
Orion Arm.
c) On pps 88-90, Dickinson describes how our Sun is being overtaken by the
Ursa Major Cluster, an old (200 million years) loose open cluster, "much
like a group of joggers running in a clump gradually overtaking and passing
a slightly slower runner. Millions on years in the future, the cluster will
be an inconspicuous patch in the direction of the star Deneb...This group
(of 5) plus about 30 other stars scattered across the sky make up the
nearest star cluster. The reason it does not look like a star cluster is
that we are inside it, although the Sun is not a member."
Burnham's goes on to name some of the other stars in this overtaking
cluster, some named celebrities, notably Sirius, as well as alpha Oph,
Raselhague, and beta Aur, Menkalinan; along with delta Leo and alpha Coma.
At that point they were wondering if these stars were all part of the
actual cluster or a larger Ursa Major stream, but it's moot to me, they all
have common proper motion. There are some 100 stars in this whole stream.
Gives you some idea of the size of a loose open cluster, that we're inside
one, some 80-90 ly across, with stars on opposite sides of us, bright and
all spread out. Vertiginous.
Some universe.
JD
Jamie Dillon <*> speech pathologist
jdillon@No-Spam
"_____" -- Harpo Marx