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Floating figures and tables ordinarily come out the same width as the page, but in two-column documents they’re restricted to the width of the column. This is sometimes not good enough; so there are alternative versions of the float environments — in two-column documents, figure* provides a floating page-wide figure (and table* a page-wide table) which will do the necessary.

The “*”ed float environments can only appear at the top of a page, or on a whole page — h or b float placement directives are simply ignored.

Unfortunately, page-wide equations can only be accommodated inside float environments. You should include them in figure environments, or use the float or ccaptionpackage to define a new float type.