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Astronomical Techniques Analysis of Moon ObservationsPowerPoint Presentation

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

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
- it’s not too late to make further positional and phase observations!

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!

Synodic Period

- Determined purely from phase observations
- Convert date to day number(2007 Feb 1 12:00 = 32.5)
- Convert phase to be monotonically increasing
- Fit straight line to obtainsynodic period and error

Class Data

- Remaining properties deduced from positional observations
- Pooled class data (152 obs) available from website http://astronomy.sussex.ac.uk/~loveday/astroTech
- 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)

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 year’s data: yours will not be identical

Line of Nodes

- Line of nodes isintersection of theecliptic plane andplane of Moon’sorbit
- Ascending nodeis South to Northcrossing

Eclipses

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

Ascending Node

- Plot ecliptic latitude versus longitude
- Nodes arewhere orbitcrosses eclipticplane
- Ascending =from –ive to+ive latitude
- Descending =ascending + 180

Precession of Nodes

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

Inclination of Orbit

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

Eccentricity of Orbit

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

Summary

- Report is due in at midday on Wednesday, 9 January 2008
- Include your observing notebook
- Don’t forget to return your cross-staff to Philip Meek or Maria Brook before the end of term and get your £10 deposit back!
- Also don’t forget to complete the course evaluation questionnaire via Study Direct

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