Long ago I spent quite a bit of time sailing with passages across the Atlantic east to west and north to south. These days most sailors use GPS and a sextant is just for backup. Celestial navigation requires equipment for sight reduction. Even the more simplified lifeboat navigation will require some equipment so these methods would be of little use to a cyclist. What would be of use are orienteering methods which rely on map and compass and keeping your wits on alert. There are many orienteering web sights where you can pick up information to study. https://www.google.com/search?q=orie...a&channel=fflb