Sea and Space / Navigation / Astronomical

## Finding your Latitude during Daytime

Now you have found your geographical longitude, you may also want to find your geographical latitude (assuming that you do not use the North Star, as explained earlier).

This is actually quite simple, once you have measured the solar conditions during the Local Noon at your place. For this, you need to consult the chapter on the solar altitude. As you will see, at any moment of the day, the height of the Sun above the horizon depends on:

- a: the hour of the day.
- b: your position.

The position of the Sun, as compared to the celestial equator is called SD - or Solar Declination. As described (in the solar altitude chapter) - this Solar Declination is tabulated for each day during a year.

In addition, the Local Noon - Sun has a height above the horizon, which depends on your geographical latitude GL. In the separate chapter, we find that the solar height at Local Noon (H; in degrees) is given as :

          H = 90 - GL + SD

Isolating GL in the equation above, gives:

          GL = 90 - H + SD

So, measuring H by a gnomon or a sextant, and finding the tabulated values for the Solar Declination SD, you may now find your own geographical latitude.

#### Exercises

1. On March 21 and September 21, the Sun is located at the celestial equator at Solar Declination SD = 0°. On one of these dates, some pupils find that the height above of the horizon of the Sun at Local Noon is H = 39°. What is their geographical latitude?

2.On June 21, SD = 23.5°. What is the height of the Sun above the horizon at Local Noon in Rome? In Stockholm? In Lissabon? Use a geographical map to read the geographical latitudes and use the first of the formula above.

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