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Re: Rising angle of stars
From: Steve E. Bryant
Date: 2014 Oct 28, 18:06 -0500

The declination is southerly and I should have reported it in negative degrees.

Sent from my iPhone

> On Oct 28, 2014, at 5:36 PM, Steve E. Bryant  wrote:
>
> I checked with Stellarium to see that Mintaka's declination is 00-17'-21".
> 17'-21" is pretty close to east at the equator.  Of the three declinations
shown one was different from the other two.
>
> Sent from my iPhone
>
>> On Oct 28, 2014, at 5:08 PM, Steve E Bryant  wrote:
>>
>> Would it be correct to assume that Mintaka's declination was zero?
>>
>> Sent from my iPhone
>>
>>> On Oct 27, 2014, at 1:47 PM, Frank Reed  wrote:
>>>
>>> When you're at the equator, all stars rise vertically from the eastern
horizon. At other latitudes, stars due east (necessarily with declination
equal to zero) rise at an angle from the vertical equal to the latitude.
While driving east through dark, rural Rhode Island last night, I was
enjoying the view of Orion's belt rising in front of me. I could trace
Mintaka back at an angle from the vertical of 41° (near enough to my
latitude) and know that this was almost exactly due east as I drove along.
That got me wondering about the rising angle for other declinations or
azimuths... At home I decided to sit down and work it out. It turns out that
the relationship is simple. If theta, θ, is the angle with respect to the
vertical for a rising (or setting) star, then
>>> tan θ = tan L / sin Z
>>> where L is latitude and Z is azimuth. For example, if the azimuth is
exactly either NE or SE as a star rises at latitude 45°, then the rising
angle is 54.7° away from the vertical. This is symmetrical north and south of
east, which surprised me a bit, though it makes sense in retrospect.
Naturally when Z=90°, the rising angle is equal to the latitude. At all
latitudes, for azimuths from 75° to 105° (within 15° of due east), the rising
angle is less than one degree greater than the latitude.
>>> -FER
>>>
>>>
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>
> View and reply to this message:
> http://fer3.com/arc/m2.aspx/Rising-angle-stars-Bryant-oct-2014-g29081
>
>
>

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