Astronomical Techniques Analysis of Moon Observations

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Astronomical TechniquesAnalysis of Moon
Observations

• Jon Loveday
• University Of Sussex
• Department of Physics and Astronomy

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Report Contents

• Using your own data
• description of observations (position phase)
• table of your observations
• plot of lunar phase against date and estimated
  value of synodic period
• its not too late to make further positional and
  phase observations!

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Report Contents

• Using class positional data, calculations of
• length of sidereal month
• position and precession of ascending node
• inclination of orbit to ecliptic
• eccentricity
• Estimate errors on all these quantities!

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Synodic Period
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Synodic Period

• Determined purely from phase observations
• Convert date to day number(2007 Feb 1 1200
  32.5)
• Convert phase to be monotonically increasing
• Fit straight line to obtainsynodic period and
  error

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Class Data

• Remaining properties deduced from positional
  observations
• Pooled class data (152 obs) available from
  website http//astronomy.sussex.ac.uk/loveday/ast
  roTech
• For each observation table includes
• Observer
• Date and day number
• RA, dec, ecliptic longitude, latitude and their
  errors
• True and mean orbital longitude (longitude
  difference from ascending node, mean for circular
  orbit)

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Sidereal Period

• Plot ecliptic longitude versus day number
• Work out which cycle each observation is in
  (check by using approximate value of period)
• Add 360o to longitudes in successive cycles
• Identify and remove outliers
• Sidereal period can then be deduced from slope of
  best fit line
• NB Following plots are from a previous years
  data yours will not be identical

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Line of Nodes

• Line of nodes isintersection of theecliptic
  plane andplane of Moonsorbit
• Ascending nodeis South to Northcrossing

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Eclipses

• We only get an eclipse at full/new moon if the
  moon is also at a node (crossing the ecliptic)

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Ascending Node

• Plot ecliptic latitude versus longitude
• Nodes arewhere orbitcrosses eclipticplane
• Ascending from ive toive latitude
• Descending ascending 180

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Precession of Nodes

• Nodes precess with time
• Precession ratecan be estimated bycomparing
  timeof crossingsover many years

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Inclination of Orbit

• Given by maximum latitude try fitting a
  sincurve to latitude vs longitude plot

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Eccentricity of Orbit

• Eccentricity may be estimated from plot of (true
  mean)orbital longitude vs true longitude
• NB not necessarily centred on 0

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Summary

• Report is due in at midday on Wednesday, 9
  January 2008
• Include your observing notebook
• Dont forget to return your cross-staff to Philip
  Meek or Maria Brook before the end of term and
  get your 10 deposit back!
• Also dont forget to complete the course
  evaluation questionnaire via Study Direct