Where is the comet 17p Holmes located in the sky from Southern California perspective?

Comet Holmes is currently near the star Mirfak in the constellation Perseus. If you look in the evening just after dark, this would be high in the north-eastern sky.

For the past couple of days I've noticed Comet Holmes seems to be dimming. This is because as the gas and debris around it (which isn't very dense) keeps expanding, there's less surface area to reflect light.

Last night I couldn't see it with the naked eye, however I still had a great view with a pair of 7x50 binoculars that showed it quite clearly.

If you need help locating the constellation Perseus, it's about halfway between the better known Cassiopeia (the big "M" or "W" that's to the north, although at the time of night you'll be looking it'll be on it's side so look for a sideways "M" or "W") and The Pleiades (the "seven sisters" - the star cluster that's to the east).

As for the other two very bright stars you mentioned, without knowing where in the sky you were looking, it's hard to say whether they were planets or not.

However, here are some clues to help you determine whether you were seeing a planet or not.

First, all planets follow a path across the sky known as the ecliptic. This is the same path that the sun and moon follow across the sky. So, if the stars you were looking at were somewhere else in the sky, they weren't planets.

Try looking, noting their positions, and then looking again every hour or two to see if they have moved. If they haven't moved, they're not planets.

The planets currently visible (Nov. 2007) are:

Mercury is in the morning sky, in the east, before sunrise. Mercury's hard to see though. For one it's very small and close to the sun, and also it never gets very high above our horizon.

Venus is also in the east before sunrise. Venus is much brighter and easier to see than Mercury.

Mars come up (rises in the east) mid-evening and is high overhead at dawn. If you face the constellation Orion in the evening, Mars will be to the "left" of it. Mars has a ruddy red appearance.

Jupiter sets in the west shortly after sunset. It should be one of the first things you see in that direction as the sky gets dark.

Saturn looks sort of cream colored and rises (in the east) shortly after midnight. Look near the constellation Leo. Saturn is high in the southern sky at sunrise.

These are the only planets visible with the naked eye.

-edit-

To Spaceguy below: in very turbulent air, even planets can appear to "twinkle", so that is not always a reliable indicator. For a detailed explanation of stars "twinkling" see this link:

http://www.badastronomy.com/bitesize/twinkle.html

One thing to remember is that when looking into the night sky planets do not twinkle, if it twinkles then its a star, chances are the brown/red object you are seeing is mars, But we have no way of knowing this,,