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Subject: Re: Planet rising
From: David Weilacher (daveweilacher@XXX.XXX)
Date: Sat Feb 02 2002 - 00:34:37 EST
Okay. I definitely mis-stated my question.
How do I determine time and azimuth of a planet rise, given:
My DR position
A nautical almanac.
H.O. 229 sight reduction tables.
Paper & pencil.
No calculator.
> [Original Message]
> From: R.H. van Gent
> To: <NAVIGATION-L@XXX.XXX>
> Date: 2/1/2002 6:25:16 PM
> Subject: Re: [NAV-L] Planet rising
>
> "daveweilacher@XXX.XXX" wrote:
>
> > So. How do you compute the time a planet rises.
>
> The same way as you do for the Sun (note that this depends both on your
> latitude and on the declination of the Sun or planet). The correction
> for the semi-diameter you can neglect, only the correction for
> refraction matters. This is about 34 minutes of arc, so you determine
> when its zenith distance is 90 degrees and 34 minutes.
>
> > I've got the meridian passage of the planet from the daily pages of the
nautical almanac. Good.
> >
> > It's true rise should occur at 90 degrees before then. Arc to time has
this convert to 6 hours earlier.
>
> Only when the planet's declination is near to 0 degrees (i.e. is near
> the celestial equator. Depending on the planet's declination and your
> latitude this interval could be significantly smaller or larger than 6
> hours.
>
> The time difference between planet rise to meridian passage (H) is given
> by the relation:
>
> cos H = (cos 90? 34' - sin decl * sin glat)/(cos decl * cos glat)
>
> Convert the angular measure H into a time interval (hours) by dividing
> it by 15.
>
> When you neglect the correction for refraction, the equation simplifies
> to:
>
> cos H = - tan decl * tan glat
>
> > Its apparent rise should have some factor for refraction. (by way of
example, the sun has 14 minutes in its 50' adjustment).
>
> See above. The 50 arc minute correction for the Sun is the sum of 16 arc
> minutes for the semi-diameter and 34 arc minutes for the refraction.
>
> Regards,
>
> =======================================================
> * Robert H. van Gent *
> * E-mail: r.h.vangent@XXX.XXX *
> * Homepage: http://www.phys.uu.nl/~vgent/homepage.htm *
> =======================================================
--- David Weilacher
--- daveweilacher@XXX.XXX
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