How can I get >15 digits in a cell of ms excel sheet

How can I get >15 digits in a cellofms excel 2010

Please clarify your question.
If it's simply a matter of 15 digits, or more, not displaying, then simply enlarge the size of the cell.
Otherwise please post back with further information.

I think I get the question,
When the cell is in "Number" format, excel will display only 15 digits and the rest will be converted to Zeros. To overcome this, you can change the cell to "Text" format, then you can type up to 1027 digits.

BK201 : That's not quite right. While you can input numbers larger than 15 digits in a "text" cell, excel will use scientific formula with it. I have been trying different formats and work arounds mentioned here and other websites and I have yet to find a way to get Excel to display more than 15 number properly. MS fail.

15 digits is enough to deal with numbers as high as 999trillion. What are the numbers being used for that are higher than that?

I was trying to use it to store SpecID numbers from the DR8 Sloan Digital Sky Servey for a research project I am working on. These numbers are 16 to 17 digits long, depending on the stellar object. Thankfully the Right Acention and Declination are not near as long.

Ouch, OK, then if these are "referential" numbers, not the kind of numbers you add/subtract on, then storing these numbers as text should be fine.

Correct, except that Excel 2007 uses scientific notation with larger numbers in a text cell and I have been unable to turn that "feature" off. I've given up trying to use Excel for this, though I would still perfer to use it if I am able.