When will Eclipses occur ?

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When will Eclipses occur ?

• Working it out for yourself

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Using Published Predictions

• You could use the predictions on the BAA VSS web
  pages
• These are very useful if you want to know which
  stars will be in eclipse tonight
• The SAC elements, rather than the GCVS elements,
  have been used for these predictions because the
  SAC elements are more up to date

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Predictions on BAA VSS web pages
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Working it out yourself

• Sometimes, however, you will want a list of
  predictions for an individual star
• For TV Cas, the SAC elements are
• Epoch (24)44602.4534
• Period 1.8125956 days
• Enter these in a spreadsheet and convert them to
  a date and time

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C4 MOD(A40.5,1)B4 A40.5-C4-15019
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Setting the date time format

• However this results in a day count (since
  1/1/1900) and a decimal fraction of a day
• Click on each cell in turn and select Cells from
  the Format drop down menu and convert them to the
  required format
• e.g. for the Date cell .

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Display the date as dd/mm/yyyy
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Predicting later eclipses

• Predictions for later dates are calculated by
  adding multiples of the period
• 1980 was many orbits ago, so this first
  calculation adds 1000 orbital periods

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A5 A4 1812.5956
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Exploiting Excel to repeat calculations

• Later predictions can be generated by selecting
  cell A5, clicking on its bottom right hand corner
  and dragging the mouse down column A

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Repeat the calculation for A6-A9
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and for columns B and C
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Add smaller multiples of the period after you
reach the current date
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Avoiding Bias

• In practice, its best not to know the predicted
  time of mid eclipse to the nearest minute
• This can be aided by leaving column C as a
  decimal fraction
• Then multiplying this by 24 and using
  Format/Cells/Number to give the time to the
  nearest hour in column D.

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D4 C424