You can definitively read data from a file using IDL. The way to read the data will depend on the file type (ASCII, binary,...) I added below a few links that point to routines to read data from files http://www.exelisvis.com/docs/READ_AS... http://www.exelisvis.com/docs/READ.html http://www.exelisvis.com/docs/READU.html

Hi Ryan, If your file contains two columns for RA and DEC with no header information, then you could do: ; Select a text file and open for reading file = '\filename.dat' OPENR, lun, file, /GET_LUN data = READ_ASCII(file, DATA_START=0) help, data ; Close the file and free the file unit FREE_LUN, lun end Since "data" is a structure, then"help, data" will show something like: FIELD1 FLOAT Array[2, 150] And to read a structure you can do the following, for example: Star 1 will have the RA and DEC given by: data.FIELD1[*,0] i.e. RA =data.FIELD1[0,0] DEC=data.FIELD1[1,0] Foe star 2 data.FIELD1[*,1]\ i.e. RA =data.FIELD1[0,1] DEC=data.FIELD1[1,1] and so on until star 150 data.FIELD1[*,150] I think that's correct. I hope that helps. Cheers, Fernando