This webpage contains large-scale WFPC2 mosaic patterns designed to increase the field-of-view for large targets. See the WFPC2 dither pattern webpage for patterns designed to improve the rejection of detector artifacts, and/or create sub-sampled data. See the pointing patterns top page for general information about WFPC2 pointing. See diagrams of these mosaic patterns projected onto the sky below. Send your pointing questions to the STScI Help Desk (firstname.lastname@example.org).
MOSAIC LINE patterns
These two mosaic LINE patterns produce large mosaic shifts when using all chips (pattern 21) and just the WF2-WF3 chips (pattern 22). They leave about 5% overlap. See Figures 1 and 2, below.
Pattern_Number: 21 Pattern_Type: LINE Pattern_Purpose: MOSAIC Number_Of_Points: 2 Point_Spacing: 99.599 Coordinate_Frame: POS-TARG Pattern_Orient: 45.00 Center_Pattern: NO
POS TARG equivalent: 0.000, 0.000 70.427, 70.427
Pattern_Number: 22 Pattern_Type: LINE Pattern_Purpose: MOSAIC Number_Of_Points: 2 Point_Spacing: 74.7 Coordinate_Frame: POS-TARG Pattern_Orient: 180.00 Center_Pattern: NO
POS TARG equivalent: 0.000, 0.000 -74.700, 0.000
Note that as shifts approach 100 arcsec, it becomes more difficult to find guide stars. So the 100 arcsec shift in patern 21 can be reduced a bit to improve scheduleability, but pattern 22 is probably a better alternative, especially due to the WF4 bias problems.
MOSAIC BOX patterns
This mosaic BOX pattern is about as large as you can hope to conduct in one visit (with one guide star pair), since the shifts add up to a diagonal shift approaching 100 arcsec. This pattern could be compressed a bit (keep reducing the spacings until you have guide stars), or it may have to be split into two visits (iterations of pattern 22). See Figure 3 below.
Pattern_Number: 23 Pattern_Type: BOX Pattern_Purpose: MOSAIC Number_Of_Points: 4 Point_Spacing: 74.700 Line_Spacing: 74.700 Coordinate_Frame: POS-TARG Pattern_Orient: 90.00 Angle_Between_Sides: 270.00 Center_Pattern: NO
POS TARG equivalent: 0.000, 0.000 0.000, 74.700 74.700, 74.700 74.700, 0.000
A special note about large long-term observing programs
For very large programs, it is impossible to obtain all the observations at the same ORIENT, and more complicated pointing strategies are required. The User Information Report available below describes how Large programs can affect the overall schedule of HST and how observers can optimize their scientific return while minimizing difficulties in scheduling their program: www.stsci.edu/hst/proposing/docs/LargePrograms/.
Figure 1: WFPC2 mosaic LINE pattern 21
Figure 2: WFPC2 mosaic LINE pattern 22
Figure 3: WFPC2 mosaic BOX pattern 23