Lowest altitude of Alkaid?

Can anyone help me with this question?
I need to calculate the lowest altitude of Alkaid at my latitude which
is
55
deg 45.9'

I found a formula for calculating the altitude at meridian transit
facing
south but not sure if I can use it to calculate the altitude looking
directly north.

The formula was
objects altitude = (90 - observers latitude) + stars declination
This works out as
(90° - 55° 45.9') + 49° 18.795'
= 83° 32.895'
Obviously this is for transit of the observers meridian looking south


I modified the formula to
objects altitude = stars declination - (90 - observers latitude)
Because it appears to give me the correct answer (15° 4.695' ) but i'm
not
sure its right and im having trouble getting my head round it lol

Does it look right?
comments?

On Sun, 02 Jan 2005 11:36:07 GMT, Paul Stephen
wrote:

Can anyone help me with this question?
I need to calculate the lowest altitude of Alkaid at my latitude which
is
55
deg 45.9'

I found a formula for calculating the altitude at meridian transit
facing
south but not sure if I can use it to calculate the altitude looking
directly north.

It is probably easier just to think about the geometry than to figure out
someone else's formula. Alkaid is rotating around the north celestial pole
(approximately, Polaris) on a circle with a radius equal to 90° less its
declination, i.e. 90°-49.3°=40.7°. When it is crossing the meridian to the
north, it will therefore be 40.7° below the pole. Since altitude of the pole is
just your latitude, you can calculate the minimum altitude of Alkaid as
55.8°-40.7°=15.1°. So the formula here is

altitude = latitude - (90° - declination)

Which is equivalent to your modified formula, so you can trust your answer.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com