Celestial Navigation Basics

• The Sun, moon and start travel across the sky in a very specific way

• Understanding the relationship of these will help you find your way

Sun and Shadows 

• From a person’s perspective, the sun moves from east to west

• Likewise, shadows move from west to east through the day

• In the Northern Hemisphere

  • When the sun at its highest point in the sky 

    • Shadows point north 

  • At lower latitudes, this may not be appreciable

  • Shadows will move clockwise

• In the Southern Hemisphere

  • When the sun at its highest point in the sky 

    • Shadows point south 

  • At lower latitudes, this may not be appreciable

  • Shadows will move counterclockwise

There are two basic shadow direction finding techniques

• Shadow-Tip Method

• Watch Method

Shadow-Tip Method

Find a relatively flat and open area exposed to the sun

1. Place a 1 meter tall stick into level ground 

   • Mark the shadow's tip with a rock or twig

2. This is your West Point

3. Wait 10 to 15 minutes for shadow to move a few centimeters

4. Mark the shadow tips new position

5. This is your East Point

6. Draw a straight line between the two marks

   • This is an East-West line

7. If you stand facing your line with the first mark to your left and second to your right, you are facing north

Watch Method

Use your watch and the sun to determine North.  

• Different technique for Northern and Southern Hemisphere

  • In Northern Hemisphere, the sun points south at noon and casts a north shadow 

• Near the Equator is a little more challenging because the sun can be north or south of you depending on the time of year 

Moon Method

You can use the light side of the moon to help guide you at night.  The direction of the light is the same throughout the night - it points at the sun.  Depending on how late it is at night determines what side of the earth the moon is on. 

Earth rotates such that the Sun rises in the east and sets in the west.  The Northern Hemisphere rotates counter-clockwise when viewed from the North Pole.

A moon rising before nightfall should have a bright side facing the Earth's West.

A moon rising after nightfall should have a bright side facing the Earth's East.

Using the Stars – Northern Skies

In the North, one star marks True North

• Polaris aka Polar Star and North Star

• Bright star centered over norther pole of earth (within 1-2.5⁰)

• Seen at 1⁰ North of equator and above

• Above latitude 70⁰ - too high in the sky to be useful 

To find Polaris

• Find the Big Dipper

  • Draw an imaginary line from the bottom outer to upper outer star

  • Extend the distance 5x the distance between these stars

  • This line points to Polaris

• Opposite the Big Dipper sits Cassiopeia

• The center of Cassiopeia points at Polaris 

Using the Stars – Sothern Skies

• There isn’t a Polaris for the Southern Hemisphere

• There is a Southern Cross

  • aka Crux

  • Cross points to a spot over horizon that is generally south

  • Made up of 4 stars, it resembles a Christian Star with small tilt

  • Don’t confuse with other “Crosses” (Diamond and False Crosses)

    • Pointer Stars point at the peak of the Southern Cross

• To use the Southern Cross

  • Draw through the top and bottoms stars of the cross

  • Extend this imaginary line ~5x (4.5) the length between these stars

  • This point sits over the horizon south of you 

Using the Stars – Bearings 

• You can use Stars as bearing points if you have a compass

• Note that Stars move across the sky over time

  • Norther stars are useful for about 30 minutes 

  • Southern stars are only useful for about 15 minutes 

  • After this time period, you will need to pick a new star

Star “Shadow” 

• Simulate a shadow from a star or planet using a taunt line

• Mark first “shadow” and wait 15-20 minutes and mark a second point

Polaris Angle

The angle of Polaris in relation to the horizon allows you to determine your latitude.

• This has long been used by mariners and other explorers

• Use a clinometer to measure an angle to Polaris

• That angle IS your latitude

• If Polaris is 50° above the horizon, then the latitude is 50°N

This is one use of the cliniometer found in higher end compasses.

Solar Angle - Latitude

The sun can also be used in a similar fashion as Polaris to determine latitude.

NOTE: do NOT look directly at the sun - you will cause irreversible damage to your eyes

• Take the sun’s angle below vertical (90° - measured angle)

• If Sun is 50° above the horizon, then the latitude is 40°N (90-50)

  • This is true at least in March and September

  • A seasonal declination of up to 23.45° must be factored in

Northern Hemisphere

Latitude = 90 – (sun’s angle at noon) + Declination

Southern Hemisphere

Latitude = 90 – (sun’s angle at noon) - Declination

Declination:

+23.45 June 22

+20 May 21, July 24

+15 May 1, August 12

+10 April 16, August 28

+5 April 3, September 10

0 Mar 21, September 23

-5 March 8, October 20

-10 February 23, October 20

-15 February 9, November 22

-20 January 21, November 22

-23.45 December 22

Solar Angle - Longitude

A good watch set to Greenwich Mean time will allow you to determine Longitude when the sun is at its highest point. 

NOTE: do NOT look directly at the sun - you will cause irreversible damage to your eyes

Each Hour past your set time the sun is at the highest point: 15°

Each Minute past your set time the sun is tat the highest point: 0.25°  (1/4° if you like fractions)

Example 1

• Highest point of sun is at 5PM Greenwich

• You are 5 hours past 12PM

• 5 x 15° = 75°W

Example 2

• Highest point of sun is at 2:30AM Greenwich

• You are 9.5 hours ahead 12PM

• 9.5 x 15° = 142.5°E   or

• (9 x 15°) + (30 x 1/4°) = 135° + 7.5° = 142.5°E