accidentals

how long does an accidental stay in effect? sometimes you see a flat or sharp followed by a natural to cancel it, other times, if it's farther along in the piece before the note repeats, there's no natural sign.

also, how do i get this image to be my avatar? it's on my hard drive right now.

An accidental stays in effect until the end of the bar (measure)

To get your image as an avatar, it has to be hosted somewhere on the internet - you can't load it from a local drive. When you have it hosted, you just go to your profile and enter the URI of wherever it is stored, e.g.

As Greybeard said accidentals are just for one bar unless cancelled within the bar.
I use http://photobucket.com/ to host my images, and it is free :D

That's the general rule - a bar line cancels all the accidentals (except those in the key signature). Oh, and an accidental only applies to the note in that octave - an F# on the top line won't affect the F on the bottom space... most publishers follow that rule.

Like so many other things in music, there are exceptions, so I thought I'd list a couple for the curious.... they're actually widely used, but only in specific genres:

In harp music, accidentals apply only to one note. Harp music doesn't use any naturals, since there's no need for them - each note is 'reset' right after its played. That has to do with the way a harp gets accidentals (by foot pedals), and that notation was invented by Carlos Salzedo, a harp professor at Curtis, and you'll usually see 'Salzedo' or 'Salz' on the first page of the score.

Then there's the twelve-tone stuff. When you get into Schoenberg and other 20th century atonal music, you've got so many accidentals you can easily forget to 'reset' them all at the bar line. So in the Second Vienna Notation (usually noted 'Vienna 2', 'VII' or '2V' on the beginning of the score) or the 'Modernist' notation, an accidental applies only to that note - unless the note is immediately repeated. Stick anything in the middle, nd the note is back to natural... so if you see C#-C-D, both Cs are sharped, but if you see C#-D-C, only the first C is sharped.

There are tons of other systems used by at least a few folks. The Music Notation Modernization Association will happily sell you a book describing about 500 different proposed methods :)