From: Patrick Wallace [ptw@star.rl.ac.uk]
Sent: Tuesday, May 14, 2002 4:18 AM
To: SoftBisqUser@yahoogroups.com
Subject: [SoftBisqUser] Re: TPoint automation
On Mon, 13 May 2002 15:31:55 Andy Forsberg wrote:

> I don't understand.  Is not the bending of light at say 45 degrees
> around .9 min or 54 arcsecs for stars.  Why then 90 arcsec correction?

It depends on where your telescope is located.  Here's a table showing
the distance between the refracted and unrefracted poles for different
latitudes and heights:

  lat     0m  250m   500m  1000m  1500m  2000m  2500m  3000m

   85     5     5      5      4      4      4      4      4
   80    10    10      9      9      8      8      8      7
   75    15    15     14     14     13     12     12     11
   70    20    20     19     18     17     17     16     15
   65    26    25     25     24     22     21     20     19
   60    32    31     31     29     28     26     25     24
   55    39    38     37     35     34     32     30     29
   50    47    46     45     42     40     38     36     35
   45    56    54     53     50     48     46     43     41
   40    66    65     63     60     57     54     52     49
   35    80    78     76     72     68     65     62     59
   30    96    94     92     87     83     79     75     71
   25   119   116    113    108    102     98     93     88
   20   152   148    145    138    131    125    118    113
   15   205   200    195    185    176    168    160    152
   10   305   298    290    276    263    250    238    227

  deg     0ft 820ft 1640ft 3280ft 4920ft 6560ft 8200ft 9840ft

If you want to set your polar axis to the refracted pole, and
you're in the northern hemisphere, aim for ME = minus the
tabulated value.  In the south aim for ME = plus the value.

Patrick Wallace
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