Sextant altitude

Question 1

What is a sextant

Answer 1

Tool for measuring angles

Question 2

What is the Zenith

Answer 2

Zenith is vertically above the person

Question 3

Sextant Altitude

Answer 3

Angle from celestial body to horizon

We apply corrections to ensure that altitude doesn’t affect angle

Question 4

What are we correcting for?

Answer 4

Dip
Refractrion
Semi Diametre
Parallax

Question 5

Dip

Answer 5

Observers Eye is above the horizon

It is Substracted

Question 6

Refraction

Answer 6

Due to the Earths Atmosphere

It is subtracted

Question 7

Semi Diametre

Answer 7

Upper or Lower Limb measured

Lower Limb added, Upper Limb subtracted

Only affects big bodies like the sun.

Question 8

Parallax

Answer 8

Angle at the surface measured but angle centre required - added

Only significant for Sun, Venus, Moon and Mars

It only affects nearby bodies

Question 9

Which Bodies does Parallax affect

Answer 9

Sun, Venus, Moon and Mars

Question 10

Order of correcting Altitude

Answer 10

Sextant Altitude
> +- Index error - on + off
Observed Altitude
> -Dip
Apparent Altitude
> +- Total correction
> Parallax for Venus, Moon and Mars
> Additional refraction correction (non standard conditions)
True Altitude
> 90 - TA
True Zenith Distance

(Suns total correction value accounts for Parallex)

For Dip its found in the nautical almanac, Read uphill if its a value