Please explain using an Artificial Horizon

Neville220

Neville220

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Hi,

I am a student of the OYM and have a Freiberger Drum Sextant, I have taken sights but never used an artificial horizon.

Could anyone explain to me, as though I am a fairly intelligent 10yr old, exactly what one is and how you use it.

Many thanks in advance

Nev
 
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Billjratt said:
It's a dish of oil placed on the ground between you and the sun when you are in a situation that you can't see a sea horizon.
You bring the sun down to it and half the measured angle.

Try drawing it.

At least, that's what I think I remember..

get one here http://www.celestaire.com/Sextant-Accessories/Davis-Artificial-Horizon/vmj_estore.tpl.html

(I assume the blue 'link' icon doesn't work in Edit)
Click to expand...

On a windless day a bucket or tray of water works OK too, and is much less messy if spilled. You can also practice moon and some brighter stars and planet sights. No good if the object altitude is more than 60 degrees, as you are measuring double the angle and halving it.
 
You use an artificial horizon if you don't have a real one handy.

Simple innit?

Like me.

(No need to thank me.)
 
Billjratt said:
It's a dish of oil placed on the ground between you and the sun when you are in a situation that you can't see a sea horizon.
You bring the sun down to it and half the measured angle.

You can use a bowl of water on a calm day and, from memory, I think you omit height of eye from the calculation too.
Click to expand...
 
nimbusgb said:
I wouldn't venture into cloud without one! Never could hack it for long on just the slip ball!
Click to expand...

Aluding of course to the similarly named instrument used in aircraft for flying when the horizon can not be seen. In an aircraft the horizon is determined by the long term location of a spinning gyro. The gyro settles to horizontal from gravity after a period of being on the ground or straight and level flying. When the plane changes attitude in roll or pitch the spinning weight of the gyro remains horizontal and this position is relayed to the pilot by levers to a needle. (or electrically sensed). The gyro is not affected by the acceleration forces produced in a climb dive or roll. The pilots inner ear mechanism is affected by acceleration forces and disorientation quickly follows unless the pilot carefully follows the information from the Artificial Horizon. (over his own instincts) In modern aircraft a laser in a ring can be used to produce the same results by sensing movement away from the original straight and level, as the spinning weight gyro. olewill
 
Artificial horizon

1) Zero for your Height of Eye.

2) Apply Index Error in the normal manner.

3) When the bottom of the reflected image is touching the top of the image in your artificial horizon it is a Lower Limb measurement. (preferred method)

4) Halve the resulting angle.

5) Apply the remaining altitude corrections to obtain your true observed altitude, Ho.
 
Porthandbuoy said:
1) Zero for your Height of Eye.

2) Apply Index Error in the normal manner.

3) When the bottom of the reflected image is touching the top of the image in your artificial horizon it is a Lower Limb measurement. (preferred method)

4) Halve the resulting angle.

5) Apply the remaining altitude corrections to obtain your true observed altitude, Ho.
Click to expand...

Hi,

Thanks for the info, very useful.

How far in front of you should the bowl be, as this would make a difference wouldn't it?

Pagan
 
Neville220 said:
Could anyone explain to me, ... exactly what one is and how you use it.
Click to expand...

This link: http://www.ybw.com/forums/showthread.php?t=230811&page=2
and my post have a link to the Longcamp article/picture, a cut-and-paste from the Davis sextant instructions, and personal observations.

From memory, the distance you stand back from the bowl is not important, the importance lies only in ergonomics - what's a comfortable distance (standing, sitting, crouching?) to line up the reflected image with the real sun/moon in the handpiece of the sextant. Comfort for me was having the bowl on a table and standing about one to 1.5 metres back, but it depends on how tall you are, the angle of the object, etc .. just getting them lined up with you being comfortable, that's all.
 
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Oil is less ruffled by the wind. I get quite close (30cm?), but then I use a small saucer of dark engine oil. As someone else on this forum pointed out, a bucket of mercury would be best! - even less effected by the wind and a much better reflection for those dimmer celestial bodies!

Both Venus and Jupiter are up at twilight at these latitudes, at nicely intersecting azimuths - got a good fix last night from the two.
 
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