Sailing Today #181 "Cheap and lazy astro"

[nigelmercier]

Sailing Today #181 May 2012 page 92 has an article "Cheap and lazy astro"; I think the author may be confused. It describes the sun's geographic position as the point on the surface of the earth along a line joining the centres of both bodies. It then says: "... In the course of a day it will trace a path at a more or less constant latitude...". There is a diagram showing this position along 16° N during the course of 8 August 2012.

Surely the tilt of the earth makes this a nonsense?

 

[stephenh]

I would not have thought so - it's the declination, surely?

I only have an old almanac but in 2008 the sun's dec. was N16 degrees and varying minutes for the whole of August the 5th, 6th and 7th, so allowing for progression it seems reasonable to me.

No ?

 

[jdc]

I think they're right

I havn't read the article,, but on the 8th August 2012 the declination of the sun is 16 deg 4.9' at 00:00 and 15 deg 47.6' at 23:59:59, so prety close to 16 deg all day.

The tilt of the earth makes the latitude over which the sun is vary from ~23.5 S to 23.5N and back over a year, so not a great deal each day. The main effect within a day is the rotation of the earth, which is 15 degrees an hour change of Longitude, but not of Latitude.

 

[ghostlymoron]

Sign up for the RYA Yachtmaster course - you'll find out all about it or buy Tom Cunnliffe's book! I did it last year and found it fascinating.

 

[alant]

Sailing Today #181 May 2012 page 92 has an article "Cheap and lazy astro"; I think the author may be confused. It describes the sun's geographic position as the point on the surface of the earth along a line joining the centres of both bodies. It then says: "... In the course of a day it will trace a path at a more or less constant latitude...". There is a diagram showing this position along 16° N during the course of 8 August 2012.

Surely the tilt of the earth makes this a nonsense?

"Sailing Today #181 May 2012 page 92"

Bit previous innit, does it also tell you what next week's lottery winning numbers are?

Sure its not March issue?

 

[dt4134]

Sailing Today #181 May 2012 page 92 has an article "Cheap and lazy astro"; I think the author may be confused. It describes the sun's geographic position as the point on the surface of the earth along a line joining the centres of both bodies. It then says: "... In the course of a day it will trace a path at a more or less constant latitude...". There is a diagram showing this position along 16° N during the course of 8 August 2012.

Surely the tilt of the earth makes this a nonsense?

One way to imagine it is to simplify things by forgetting about the relatively small movement of the E around the Sun. Then if you just imagine the Earth & Sun fixed in position, with the Earth spinning, the line between the centre of both would be an exact line of latitude drawn around the surface of the Earth.

Add back in the Earth moving in orbit around the sun and there'll be a small amount of change due to a small change in the Sun's declination, which gives you the "more or less...".

 

[nigelmercier]

2008 the sun's dec. was N16 degrees and varying minutes for the whole of August the 5th, 6th and 7th...

Perhaps it's because it's August? I can't get my head around this, need to play with a globe...

And yes, it is the May issue. It seems that ST is going the same way as computer magazines, and forward dating the issue to make them seem newer on the shelves.

 

[BobPrell]

I havn't read the article,, but on the 8th August 2012 the declination of the sun is 16 deg 4.9' at 00:00 and 15 deg 47.6' at 23:59:59, so prety close to 16 deg all day.

Yes, that is 17' for the day. For the sun, most sights will be taken between 09h and 15h, which is only 1/4 of the day. Therefore there will be about 4' change during that time.

So Nige, what have they gone on to anyway?