Dip Short in Celestial Navigation

For those that practice Celestial Navigation in Coastal, Inland or locations where a proper sea horizon can't be obtained - a correction can be made to compensate for that shortfall - it is call Dip Short, for when the distance to a natural sea horizon is shorter. Of course this won't be of much use other than to practice obtaining your sights because in those locations you really ought to know where you are anyway through other means.

My source for this is John Karl's Celestial Navigation in the GPS Age.

The simple formula is...

DipShort = 0.415767 x d + 0.565786 x h / d, where d is distance in nm and h is height in feet

Or the following Table...

Celestial Navigation Videos by Navigation Training...

I came across the YouTube channel just recently. A terrific primer on CelNav filmed on location off a sailboat and beaches of the West Indies - I will go there for this course anytime!

The YouTube channel for all videos can be found here...

https://www.youtube.com/playlist?list=PLah9ocjQNN0Zr7-oKE58wTzXE4XaQU64E

The intro here...

A number of resources - books, sites, etc. can also be found on this related web site...

http://www.practicalnavigator.org/

Well done Chris Nolan.

Have fun!

Artificial Horizons...

Boats are out of the water, no horizon anywhere to be found - what is a guy to do to get a sight around here?

It is called an Artificial Horizon and it looks like this...it is an indoor and outdoor solution complete with shaded panels for sun shots...

from Davis Instruments

Fill it with water or some other viscous fluid and off you go.

Don't forget to halve the altitude when you do the sight reduction.

This one you can use in your backyard, it is contained and helps to keep the wind from stirring up the reflection and the sight. The principle is that you get a double angle of sight through the reflection and the object when no horizon is visible, ie. many miles ashore and on land. It allows you to practice taking sights during the long. cold winters ashore - as long as you have a celestial body available and it doesn't remain hidden in cloudy skies, backyard trees and other house's rooflines.

Here is how and why it works...

If you can see it - you can shoot it.

Here is my indoor solution - minus comfy chair and coffee cup...

A Tub of Water is All You Need!

All you need is a bowl of water - filled to the brim to catch low angle bodies - sitting or standing still so that the vibration through the floor keeps the water still. I have read that the use of molasis or maple syrup can be used as a more viscous liquid to keep the things from getting stirred up.

I have a small aperture of sky available to me but have successfully been able to shoot the sun, moon, planets and stars from the warm and cozy confines of my nook overlooking the backyard deck and southern, southwestern sky. The indoor approach is limited by the amount of visible sky you have while the outdoor approach is limited by the same - although more sky may be visible but impacted by wind on the water or other reflective liquid, and possible vibrations through deck or ground vibrations, ie. a train , truck or bus rumbling through nearby.

Through this approach, you don't need to do running fixes as the old 'Stone Frigate' never moves. You can practice taking sights and plotting continuously to see how you do under various conditions.

Some of the conditions that I have dealt with are as follows...
- taking quick sights before an oncoming cloud obscures the sun
- waiting for a body to get past the roof eave of a neighbouring house to get a clear sight
- estimating where the sun's lower limb is - as it is partially obscured by tree branches in the foreground
- raising or lowering the artificial horizon in order to obtain a higher or lower angle body
- leaning around various hanging indoor objects to get a shot to the outdoors
- windy days that cause ripples inside the house

Planets and stars are caught as pinpricks and overlayed over each other to take a sight - wear your glasses as distortions cause errors. Sun and moon sights are index mirror images kissing reflected horizon mirror below as lower limb sights - and vice versa as upper limb sights. Or you can overlay both objects directly over top of each other and applying the main correction for stars, not LL or UL for the Sun. Take multiple sights and average them out.

A modification must be made to shoot stars and planets as their reflections won't be seen in the water. I have been successful in floating a small mirror on a piece of wood, and gotten some very accurate sights. Don't let the wood float in the water bath too long as it will get waterlogged and possibly not remain level. Make sure mirror and any windows you are sighting through are clean so that maximum light can be captured.

The modification to allow planet and star shots...

A Small Makeup Mirror on a Piece of Wood Floating on Water

My goal in all this is to be dealing with all manner of weather conditions in order to be able to be quicker and more accurate in taking sights. It is also a lot of fun to wake up early - not to deal with the twilight observation period - to shoot stars and planets whenever you want - at any time of a clear night.

You have to be sure that the wood has not become waterlogged and therefore not level. If a star sight does not compare favourably with the altitude on Stellarium, I know that I need to replace the wood. I may need to consider sealing the wood or finding something else that will float at level in order to get accurate sights.

If only there was a way to create an artificial horizon that would allow you to shoot stars and planets at night on a heaving boat.

You could even imagine setting things up so that you can be taking sights from your easy chair, coffee nearby, you are nice and warm - listening to your favourite music. How bad can that be?