Almanac running slow

[Dave Vaughan]

In the Almanac section the sunrise is off as compared to other weather stations in the area. I have the correct time,  ntpdc reports stratum 3. The coordinates are dead on. What else should I be checking?

Here is the html output from weewx:

Today's Almanac

Sun

Start civil twilight:	06:55
Sunrise:	07:28
Transit:	13:51
Sunset:	20:15
End civil twilight:	20:49
Azimuth:	158.6°
Altitude:	43.5°
Right ascension:	9.1°
Declination:	3.9°
Solstice:	21-Jun-2013 07:04
Equinox:	22-Sep-2013 22:44

Moon

Rise:	00:27
Transit:	04:08
Set:	08:56
Azimuth:	285.3°
Altitude:	-37.1°
Right ascension:	227.9°
Declination:	-18.2°
New moon:	10-Apr-2013 11:35
Full moon:	25-Apr-2013 21:57
Phase:	Waning gibbous (88% full)

The closest weather station reports:

Sunrise = 05:56
Sunset = 18:39

I have not looked at other calculated values yet, will do so when I understand why sunrise and sunset are off. Just know that I have done something wrong somewhere, but staring at it does not seem to be helping much. Can someone suggest where I may have made a mistake and should be looking.



Best regards,
Dave Vaughan

[Thomas Keffer]

There are some comments about this in the Almanac section of the Customizing manual. The Navy publications that you may be seeing use a horizon that is lower than what pyephem uses, resulting in an earlier sunrise. 

There are instructions in the Almanac section for replicating the Navy publications should you wish to do so.

-tk

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[AdamHI]

Being over an hour different suggests more than just a difference between calculation algorithms. I've seen some numbers differing by only a few minutes.

Not to be too flip - when you look out the window - roughty what time is the sun rising / setting?

First thought to get things closer is Daylight Savings Time -vs- Standard Time, could that be an issue?

You mention the coordinates are dead on - in decimal degrees? Perhaps you could post the portion of weewx.conf with the coordinates, maybe xxx'ing out the the digits beyond the 2nd  decimal (if you don't want to pinpoint your exact location), and tell us which city you are in. I make all kinds of bone-headed mistakes - and i'm not good at proofreading my own mistakes.

--adam

[Dave Vaughan]

Hi Adam, I tried the changes Tom said to look at, that seems to only alter the sunrise by seconds, at least it showed no difference to me. The sunrise was at 08:24 before the change and 08:24 after the change. My problem must be something much simpler. Since my first post we have changed from winter time to daylight savings time, yesterday morning. All of my unix boxes changed time just fine and their times are correct, including the one weewx is running on. All boxes run ntp. I was up before the sun came up this morning and it came up at 06:50, just as all of the weather stations in my area are reporting. Weewx is reporting the sunrise at 08:24, one hour and 14 minutes slow. My first thoughts were daylight savings time, but the 14 minutes put me off of those thoughts.

Here is a snippet from weex.conf

[Station]

    #
    # This section is for information about your station
    #

    location = "Au i. d. Hallertau, Oberbayern, Deutschland"

    # Latitude, longitude in decimal degrees
    latitude = 48.560
    longitude = -11.784
#    latitude = 48.560735
#    longitude = -11.784903

    # Altitude of the station, with unit it is in. Normally this is
    # downloaded from the station, but not all hardware supports this.
    # altitude = 476 meter

Output from "sudo ./wee_config_vantage /etc/weewx/weewx.conf --info"
Davis Vantage EEPROM settings:

    CONSOLE TYPE:                   VantagePro2

    CONSOLE FIRMWARE:
      Date:                         Apr 16 2012
      Version:                      3.00

    CONSOLE SETTINGS:
      Archive interval:             600 (seconds)
      Altitude:                     1561 (meter)
      Wind cup type:                large
      Rain bucket type:             0.2 MM
      Rain year start:              1
      Onboard time:                 2013-04-01 09:11:21

    CONSOLE DISPLAY UNITS:
      Barometer:                    hPa
      Temperature:                  degree_10F
      Rain:                         mm
      Wind:                         km_per_hour

    CONSOLE STATION INFO:
      Latitude (onboard):           48.5
      Longitude (onboard):          11.7
      Time zone code:               20
      Use manual or auto DST?       AUTO
      DST setting:                  N/A
      GMT offset:                   +1.0 hours
      Use GMT offset or time zone?  TIME_ZONE

    RECEPTION STATS:
      Total packets received:       12909
      Total packets missed:         0
      Number of resynchronizations: 0
      Longest good stretch:         12909
      Number of CRC errors:         0

    BAROMETER CALIBRATION DATA:
      Current barometer reading:    29.661 inHg
      Altitude:                     1561 feet
      Dew point:                    42 F
      Virtual temperature:          72 F
      Humidity correction factor:   19
      Correction ratio:             1.056
      Correction constant:          +0.002 inHg
      Gain:                         0.000
      Offset:                       -49.000


H,mmmmm just noticed that the altitude in the ouput from the station is wrong

1561 (meter)  -- should be 476 meter, but 476 meter = 1561.67979 feet
Could that be the problem? No, that would make the sun come up earlier wouldn't it. Looks like it is just a cosmetic problem.
I checked the console, it says 476 meter, just like I input it back when I first configured the station.

date on my unix system returns:
 Mon Apr  1 09:25:50 CEST 2013

ntpdc> sysinfo
system peer:          europium.canonical.com
system peer mode:     client
leap indicator:       00
stratum:              3
precision:            -23
root distance:        0.07761 s
root dispersion:      0.05579 s
reference ID:         [91.189.94.4]
reference time:       d503b1cb.d43b1059  Mon, Apr  1 2013  9:12:11.829
system flags:         auth monitor ntp kernel stats
jitter:               0.002884 s
stability:            0.000 ppm
broadcastdelay:       0.000000 s
authdelay:            0.000000 s


I don't know what else would effect the sunrise calculation, hope someone has a good idea.

Thanks in advance,
Dave Vaughan
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[Thomas Keffer]

My apologies, Dave. I just glanced at your post and thought I knew the answer. I didn't look closely enough to see that you're getting an hour difference. Naturally, that's way too much to be explained by subtle differences in where the horizon would be.

Still, the answer is very simple: you have specified your longitude as -11.784. It should be +11.784. The 23 degree error in longitude would result in roughly an hour and a half error in sunrise/sunset.

-tk

-tk

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[Dave Vaughan]

Tom, you are a Gentleman and a Scholar! I stared right past that minus sign, guess I have been looking for this for over two weeks now. Just knew it was something dumb that I had done, and it was.

I changed it and now the world is back in order. Times are all correct now.

Thanks a million!

Dave Vaughan

[Jon Adams]

Well, I thought my problem was pretty unique - the almanac was 14 hours off. Of course, I discovered that I'd left out that important little minus sign in the longitude.

Search and ye shall find!

Cheers - Jon N7UV