To determine whether a flare observed by an instrument on the Earth-Sun line could have been seen by MESSENGER, use the SSW routine messenger_flare_angle. You must have the spex branch of SSW in your IDL path. angle = messenger_flare_angle( [xloc,yloc], time ) or angle = messenger_flare_angle( [xloc,yloc], time, mess_helio_lonlat=mess_helio_lonlat ) where [xloc,yloc] is the location of the flare on the solar sphere in heliocentric coordinates (2-D Cartesian coordinates on the disk of the Sun as seen from Earth, [0.,0.] at the center of the disk) in arceseconds. Can be an [2,n] array for n flares. time is the date and time of the observation in anytim format. Dimension of time should agree with number of locations in xloc,yloc. mess_helio_lonlat is an optional output keyword to return the Stoneyhurst longitude and latitude in degrees of the sub-satellite point of the Sun to Messenger vector The value returned is the angle in degrees between the Sun-Messenger vector and the vector from Sun Center to the flare location. An angle of more than 90 degrees means the chromospheric footpoints of the flare are occulted by the solar limb as seen from MESSENGER. The angle is always positive, i.e. does not contain east/west direction information. N.B. The coronal portion of the x-ray flare plasma may still sometimes be seen from as far as 20 more degrees beyond the limb and thus an event may only be partially occulted Examples: print, messenger_flare_angle( [0, -100.], '17-dec-2013') 156.48918 print, messenger_flare_angle( [0, -100.], '17-dec-2013', mess_helio_lonlat=mess_helio_lonlat) 156.48918 print,mess_helio_lonlat 158.874 -3.37532 print, messenger_flare_angle( [[0, 0.],[0,-100.]], ['1-jun-2007 15:00','17-dec-2013'], mess_helio_lonlat=mess_helio_lonlat) 49.259515 156.48918 print,mess_helio_lonlat -49.2484 -2.41473 158.874 -3.37532 print,messenger_flare_angle([720,-310], '6-jul-2012') 95.009553