Why does Calpurnia object to Caesar's going to the capitol?

In William Shakespeare's The Tragedy of Julius
Caesar, the reader encounters an array of characters who exhibit a variety of
personality traits.  While some characters are purely good, others are purely evil; a few are a
mixture of the two, such as Brutus, who is conflicted and has to choose whether to remain true as
Caesar's friend, or to give in to his desire for power.  Calpurnia, Julius Caesar's loving wife,
is good.

In Scene ii of Act II, Calpurnia attempts to order her
husband to remain home all day, despite his arguments.  Calpurnia tells her husband that she has
become frightened not only by the meteors and comets they have witnesses streaking across the
night sky, but also by the terrifying sights seen by the town's watchmen.  Calpurnia considers
them to be bad omens, despite the fact that she has never been a superstitious
person. 

...A lioness
hath whelped in the streets,

And graves have yawned, and yielded up
their dead;

Fierce fiery warriors fought upon the
clouds

In ranks and squadrons and right form of
war,

Which drizzled blood upon the
Capitol;

The noise of battle hurtled in the
air,

Horses did neigh and dying men did
groan,

And ghosts did shriek and squeal about the
street.

O Caesar, these things are beyond all
use,

And I do fear them...

When beggars
die, there are no comets seen;

The heavens themselves blaze forth
the death of princes.