Azimuth & Altitude on Dob

[richardda1st (Richard)]

All made and assembled, but not quite right yet.
Will post some pics and notes when sorted, for anyone who may be interested.

I'm having trouble getting the azimuth to read as per Stellarium & Cartes du Ciel software.

Can someone see where I'm going wrong in my setup?

To get my azimuth/altitude for a given target I:

1. check my location's longitude/latitude using google and others from the net and set this into Stellarium & Cartes du Ciel (37d 41m 54s SOUTH / 144d 33m 47s EAST).

2. set the software time by taking off daylight saving time from the computer, and as I am 5.5degrees west of AEST at 150d I also move my time back by 22 minutes (5.5x4)

3. get jupiters and Rigels az/alt, for a given time.

4. calibrate the inclinometer by centering the scope to Jupiter using a 6mm ep.

5. zero the inclinometer with Jupiter centered in the 6mm ep.

6. lower the scope to horizontal till the inclinometer reads Jupiters alt, and reset to zero again,and back up to Jupiter which should read the previous alt setting. This I think is an accurate way to set the inclinometer.

7. turn my azimuth scale to Jupiter's az with Jupiter centered in the 6mm ep.

8. to check all this out I turn my scope to Rigel and take the readings.


While the altitude is close to within 1 degree (keeping in mind that the az/alt are constantly changing), the azimuth reading is up to minus 7 degrees out.

The azimuth scale I made myself using cad and professionally printed onto a full size sheet.
I'm pretty sure it's accurate.

Where am I going wrong?: screwy:

Anyone


Richard

[DavidU (Dave)]

Is the time wrong? 15 deg per hour, seems like that 22min is wrong some how.

[richardda1st (Richard)]

Hi David.
What do you mean?

15d per hour = 4m per 1d.
Is this wrong?

[JethroB76 (Jeff)]

Originally Posted by richardda1st

2. set the software time by taking off daylight saving time from the computer, and as I am 5.5degrees west of AEST at 150d I also move my time back by 22 minutes (5.5x4)

Just have your computer time set normally; I've never had to change my computer time in the several years I used a similar setup

[bojan]

Originally Posted by JethroB76

Just have your computer time set normally; I've never had to change my computer time in the several years I used a similar setup

Exactly right.
CdC takes into account day light saving if it is enabled by system.. However, because Australia is different from the rest of the world, automatic sync with internet does not work yet (it will be at the end of Oct).
Also, CdC takes care of position too.. so if you fiddled with this, there goes your 7 degrees.

[DavidU (Dave)]

Forget daylight saving.

[richardda1st (Richard)]

Thanks all,

Not to sure if I follow yet.
I will check the software parameters again.

[gary]

Originally Posted by richardda1st

I'm having trouble getting the azimuth to read as per Stellarium & Cartes du Ciel software.

Hi Richard,

On Cartes du Ciel ...

Select Preferences -> Date/Time and set Time=UTC + 11
Check that the local time displayed in that menu is the current local time
(i.e. Australian Eastern Daylight Time).

Select Preferences -> Position of Observatory
Again set Time=UTC + 11.
Set your Latitude and Longitude.

... and as I am 5.5degrees west of AEST at 150d I also move my time back by 22 minutes (5.5x4)

Don't do this. Simply enter your local Australian Eastern Daylight
Time. Cartes du Ciel will internally compute what is known as your Local
Apparent Sidereal Time (LAST) for you based on UTC time (which is
computed by the arithmetic when you entered TIME=UTC + 11)
and your longitude, plus corrections for some other jazz you don't need
to know about such as correction of UTC to UT1 and correction for nutation
provided by what is known as the equation of the equinoxes.

In a nutshell ...
Upon entering your correct time zone (UTC + 11) and upon ensuring that Cartes
du Ciel displays the correct local time in the Date/Time menu and upon
entering UTC+11 and your Lat/Lng in the Position of Observatory menu,
Cartes du Ciel will correctly compute the topocentric Az/Alt positions of
objects for you.

Best regards

Gary Kopff
Mt Kuring-Gai

[richardda1st (Richard)]

While trying to sort this out my daughter pointed out that while we're on daylight saving time , my computer is not recognising this fact as we have started DS time earlier then normal. Her up to date laptop doesnt have this problem.

Just finished checking CdC,I found that my UTC was staying on +10. Checked on my daughters laptop and the UTC auto changes to +11. So like you all said forget daylight saving.


Thanks Gary, just logged in and found your post.
Wasn't aware that CdC adjusted the time for local time according to the co-ordinates.


As bojan said "so if you fiddled with this, there goes your 7 degrees".
But its good to fiddle, make mistakes, etc.

Now hoping for some clear sky to test it all out.
Maybe at Snake infested Valley this saturday.

Thanks again to all
Richard

ps Maybe my next upgrade will be an Argo navis, any comments.

[JethroB76 (Jeff)]

Originally Posted by richardda1st

ps Maybe my next upgrade will be an Argo navis, any comments.

A good idea

[gary]

Originally Posted by richardda1st

Thanks Gary, just logged in and found your post.
Wasn't aware that CdC adjusted the time for local time according to the co-ordinates.

Hi Richard,

Another good example of "why do the calculations when a computer can do it".

What will be important to the program is the UTC time and your lat/long.
The UTC time it will derive simply from your current local time setting
and time zone (+10 hours for AEST and +11 for AEDT).

So getting the time zone and local time right then allows it to perform
the arithmetic to obtain UTC.

But even then UTC is just used to help derive other time scales.

Internally, planetarium programs are mainly computing using sidereal time rather
than civil time. For example, during the course of a year, the Earth rotates
one more time with respect to the stars than it does to the Sun. This makes a solar
day about 3 minutes and 56.4 seconds longer than a sidereal day. In other words, a
sidereal second is not the same as a regular civil time second. Subtleties
such as this are again taken into account by the program but conveniently
all you have to do is enter your own civil time, time zone offset and lat/long
and the program will do all the tedious calculations.

ps Maybe my next upgrade will be an Argo navis, any comments.

Pity you can't be at the IceInSpace AstroCamp this weekend where some lucky
soul will walk away with a discount voucher as one of the sponsored prizes.

Anyway, hope the weather is good this weekend in Snake Valley!

Best Regards

Gary

[richardda1st (Richard)]

Thanks Gary, but sacrifice Snake Valley for the Hunter Valley, fair shake of the sharaz bottle.