Re: How did Columbus know which way he was going, did he use the stars?

Being a humble British Astronomer I am afraid to say that Christopher Columbus and his exploits are not on my list of specialist subjects. Consequently I shall not embarrass myself by pretending I know what I'm talking about only to be inundated with e-mail from every American of school age and above pointing out my misconceptions!

What I have done is to find a very comprehensive web site chronicling Columbus' voyages including information on his preferred navigation techniques, The Columbus Navigation site. It seems that Columbus was not impressed with celestial navigation and decided instead to use a method known as dead reckoning. I shall let the web site explain. Here's a little about celestial navigation anyway.

Sailors navigate by the stars by comparing what they measure the position of celestial objects, Sun, Moon, planets, stars, to where they should appear if you were looking at them from a reference position, e.g., from Greenwich in England. The discrepancy between the position you observe and the position the same object at the same time would have at Greenwich can be used to calculate your current position. A good if a little in-depth explanation is given at the Celestial Navigation site.

I must point out is that Columbus did many great things but to my knowledge he never sailed in the southern hemisphere. It is an interesting point, however. You are correct in that celestial navigation becomes difficult in the southern hemisphere for northern hemisphere sailors. The first problem they encounter is that there is no equivalent bright star at the south pole as there is for the north pole where Polaris shines so brightly; this however is a trivial problem. The real problem with navigating in the southern hemisphere was that the first sailors did not have accurate data on the positions of the stars in the southern hemisphere. They couldn't be seen from Greenwich and so you have no reference to compare with. In fact the first sailors to sail around the tip of Africa. Got this far by hugging the coastline. They did not know where they were going but the knew if they turned around they would find home. As accurate star charts of the Southern hemisphere were made the problem started to dissolve.

There are many sites on the internet that display star charts if you want to see the southern constellations. I've had a quick look and although Im sure there are plenty out there that are equally as good if not better but skymaps.com looks quite good.