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Old 04-24-2014, 01:38 PM
 
1,690 posts, read 2,050,074 times
Reputation: 993

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Quote:
Originally Posted by Mac15 View Post
8pm


Lovely evening.
And this is 5.9 degrees above horizon

20:00 on 24/4/2014
50 minutes before sunset at 8:50pm

Matches these

15:48 on 24/1/2014
61 minutes before sunset

17:04 on 24/2/2014
49 minutes before sunset

18:03 on 24/3/2014
46 minutes before sunset

20:00 on 24/4/2014 "today"
50 minutes before sunset

20:47 on 24/5/2014
57 minutes before sunset

21:10 on 24/6/2014
60 minutes before sunset

20:50 on 24/7/2014
54 minutes before sunset

19:52 on 24/8/2014
48 minutes before sunset

18:35 on 24/9/2014
47 minutes before sunset

17:17 on 24/10/2014
51 minutes before sunset

15:09 on 24/11/2014
63 minutes before sunset

14:51 on 24/12/2014
72 minutes before sunset

Mac15 solar elevation angle equivalents for the evening photo taken, adjusted for DST, for NW Ireland 54"54"N 7"00W
And time remaining till sunset

For 24th of each month of 2014

Last edited by EricS39; 04-24-2014 at 02:09 PM..

 
Old 04-24-2014, 01:52 PM
 
Location: North West Northern Ireland.
20,652 posts, read 23,800,581 times
Reputation: 3107
Quote:
Originally Posted by EricS39 View Post
And this is 5.9 degrees above horizon

20:00 on 24/4/2014

Matches these

15:48 on 24/1/2014

17:04 on 24/2/2014

18:03 on 24/3/2014

20:00 on 24/4/2014 "today"

20:47 on 24/5/2014

21:10 on 24/6/2014

20:50 on 24/7/2014

19:52 on 24/8/2014

18:35 on 24/9/2014

17:17 on 24/10/2014

15:09 on 24/11/2014

14:51 on 24/12/2014

Mac15 solar elevation angle equivalents for the evening photo taken, adjusted for DST, for NW Ireland 54"54"N 7"00W

How low does sun go tonight.
 
Old 04-24-2014, 02:12 PM
 
1,690 posts, read 2,050,074 times
Reputation: 993
Quote:
Originally Posted by Mac15 View Post
How low does sun go tonight.
Min 22.1 degrees below horizon

At 1:26 in the morning

I added in the time remaining till sunset based on the time the photo was shot

Interesting to note the sun sets faster around the equinoxes

Summer sun sits longer in the late evening before fully setting

Winter noon may be low sun, but it does sit out for a while at that low angle before it dips under

The more north you go towards the arctic circle, the more slow the sun sets around the solstices. Once you go above the arctic circle, you can't even measure this out to the solstice because sun won't set at all on some of the nights. But fastest sunsets on equinox is true for all latitudes except right around the poles

Last edited by EricS39; 04-24-2014 at 02:41 PM..
 
Old 04-24-2014, 06:15 PM
 
4,658 posts, read 3,641,551 times
Reputation: 1344
Quote:
Originally Posted by EricS39 View Post
And this is 5.9 degrees above horizon

20:00 on 24/4/2014
50 minutes before sunset at 8:50pm

Matches these

15:48 on 24/1/2014
61 minutes before sunset

17:04 on 24/2/2014
49 minutes before sunset

18:03 on 24/3/2014
46 minutes before sunset

20:00 on 24/4/2014 "today"
50 minutes before sunset

20:47 on 24/5/2014
57 minutes before sunset

21:10 on 24/6/2014
60 minutes before sunset

20:50 on 24/7/2014
54 minutes before sunset

19:52 on 24/8/2014
48 minutes before sunset

18:35 on 24/9/2014
47 minutes before sunset

17:17 on 24/10/2014
51 minutes before sunset

15:09 on 24/11/2014
63 minutes before sunset

14:51 on 24/12/2014
72 minutes before sunset

Mac15 solar elevation angle equivalents for the evening photo taken, adjusted for DST, for NW Ireland 54"54"N 7"00W
And time remaining till sunset

For 24th of each month of 2014
According to wikipedia, the formula is solar noon +/- arccos ( -(sin(L)*sin(D) - sin(a)) / cos(L)*cos(D) ) / 15, with L = latitude, D = sun declination, a = sun angle (here 5.9 deg). But you said that you calculate those times with your excel model. How to calculate arccos (inverse cosine) with excel?
 
Old 04-24-2014, 08:00 PM
 
1,690 posts, read 2,050,074 times
Reputation: 993
Quote:
Originally Posted by divisionbyzero0 View Post
According to wikipedia, the formula is solar noon +/- arccos ( -(sin(L)*sin(D) - sin(a)) / cos(L)*cos(D) ) / 15, with L = latitude, D = sun declination, a = sun angle (here 5.9 deg). But you said that you calculate those times with your excel model. How to calculate arccos (inverse cosine) with excel?
Inverse cosine in excel is =(acos(value))/(3.1515927/180)

I also use a formula for the angle of declination and another formula for equation of time (the forms of these that factor the earth's eccentric orbit and for example, recognize that earth spins slower in January and faster in July and that the time length of northern hemisphere summer is 6 days longer than Southern Hemisphere summer

And also I have an adjustment for the angle of declination within the fraction of the day as it is continuously changing

Also I adjust for longitude degrees and timezone and DST

So there's a couple moving pieces

Also not every year is the same.

But you get close enough approximation if you use the solar elevation angle formula, convert hour angle by dividing by 15 like you said. Find the solar noon time around the longitude you are interested in using. Solar noon minus 12 will convert your solar time to clock time if you adjust by that amount of minutes.

And for sunrise assume a solar elevation angle of -0.83, not 0

Actually for solar elevation angle formula, you would need to convert the clock time to solar time, convert that to the hour angle to plug in, then all you need is latitude and angle of declination

Last edited by EricS39; 04-24-2014 at 08:14 PM..
 
Old 04-24-2014, 08:31 PM
 
1,690 posts, read 2,050,074 times
Reputation: 993
Today's angle of declination is 13 degrees north

Today's equation of time correction to minutes is subtract 2 minutes from all longitudes that are multiples of 15, then add an hour for DST

So longitude 0 solar noon is roughly 12:58 then add 4 minutes for every longitude degree west of starting point

That makes 7 degrees west longitude have a solar noon of 12:58 + 28 minutes which comes to 1:26pm

Want the solar elevation angle at 8pm? You have to subtract an hour and 26 off it ...the 1:26 from 12

That means the solar time of 18:34
Concert to decimals that's 18.56

You need the hour angle of 6.56 times 15

The latitude 54.9

Angie of declination 13
 
Old 04-25-2014, 03:05 AM
 
Location: North West Northern Ireland.
20,652 posts, read 23,800,581 times
Reputation: 3107
6:02
8:52
 
Old 04-25-2014, 03:17 AM
 
4,658 posts, read 3,641,551 times
Reputation: 1344
Quote:
Originally Posted by Mac15 View Post
6:02
8:52
So what's your temperatures?
 
Old 04-25-2014, 03:18 AM
 
Location: North West Northern Ireland.
20,652 posts, read 23,800,581 times
Reputation: 3107
Its only 15c
 
Old 04-25-2014, 03:20 AM
 
4,658 posts, read 3,641,551 times
Reputation: 1344
33 C (91 F) and drizzling, but sun still strong
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