Limit Loop to 5 Posts?

Heres my current loop:

<?php if ( ! empty ( $GLOBALS['post'] ) && is_single() && in_category( 'movies', $GLOBALS['post'] ) ) :
$movies = new Wp_Query('tag=movie-reviews'); 
while ( $movies->have_posts() ) :
$movies->the_post(); ?>

<?php get_template_part( 'sidebar-reviews', get_post_format() ); ?>
<?php endwhile; ?>
<?php else : ?>
<?php get_template_part( 'no-results', 'index' ); ?>
<?php endif; ?>