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Use of ephemerides from european longitudes

javi_goagc
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Joined: 2012-01-28

Hello again,

I hope my question is not too silly, but I´m still a newbie and have a doubt about the use I (as an european observer) can make of AAVSO´s predictions&bulletins.

I was planning my observing session when I realized that the AAVSO yearly bulletins, as well as the eclipsing binary&long period predictions, have been calculated and are valid for american longitudes. The same applies to the extended Milwaukee list of predictions.

¿Is there an easy way to "transform" them to european longitudes? (I´ve tried to obtain an answer to this by myself through forums search and internet surfing but have not found any clear statement on this topic). I´ve also found that there is a software tool for MS-DOS O.S. called EBMin23, by Bob Nelson,  and after downloading and executing it,  I think I could generate a customized ephemerides list depending in the longitud and latitute of the observer (though one must fill-in an excel containing some variable stars data, as far as I understand).

Also I´ve discovered the BAAVSS site, which includes some interesting estimations.

I live in an area with Greenwich timezone, although at +28º North latitude (Canary Islands, Spain).
 If I´m not wrong, I think I can make use of the same prediction times calculated for England (e.g. from BAAVSS), and the only special thing I must take into account (due to the different latitude) is the fact that there could be stars in such ephemerides that are placed too north in the sky for my observing site (cos' I´m more than 20 degrees south from England) .

Thanks in advance for your feedback and best regards!

Javier

EB ephemerides from European longitudes
BGW
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Joined: 2010-10-03

Hi Javier, I'm sorry for the delayed reply.  Thank you to Mike Simonsen for alerting me to your question.  I don't usually check the forums.

You've raised an excellent question!  I don't have a really good solution for you -- it is something we'll need to work on.  However, there is a "workaround".

First, some explanation.  An ephemeris generated in UT is valid anywhere on earth.  The star *will* be in eclipse at that time!  However, it might not be visible because the earth is between you and the star... and the sun may be up at your location!  So, the AAVSO ephems, as you've pointed out, won't be useful because they only list eclipses that are visible from North America.   The problem is not the calcuation of the ephemerides, but the selection of which ones are listed.

Here is a workaround: you can use the AAVSO ephemerides, or the Milwaukee ones, to alert you to what stars are "up" at night around a certain date (that is the same, anywhere on earth, it will just occur at a different UT).  Then, once you've identified the stars that might be good targets, you can use the Cracow site to get eclipse predictions for those stars.  Here is the link: 

http://www.as.up.krakow.pl/ephem/

Choose the constellation, and then the star.  It will give mid-eclipse times for the next 7 eclipses.  It uses civil time (not UT) based on the time zone reported by your computer.  It does no selection re sky darkness, so you'll have to do that yourself.

This is not as simple as an ephemeris customized for your location, but it is available right now.

Another option, is Shawn Dvorak's site:

http://www.rollinghillsobs.org/

Select "Ephem Generator".  I haven't used this site, but it looks like it might be useful to you.  It does select based on your location (the lat/long you enter).

I hope this helps... I'll try watch this forum for a little while in case you have more questions,

Kind regards,  Gary Billings

 

P.S.  your question is useful:  I don't use the ephemerides myself, so I had failed to recognize this problem for "overseas" observers!

Thanks!
javi_goagc
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Joined: 2012-01-28

Hello,

Thanks a lot for your help, I really appreciate your time and support, Gary, Mike Simonsen and all the involved staff! Now I have concepts more clarified.

I´m also sorry I haven´t been able to give you an answer before now.

I will try with the options you have mentioned, both using the Cracow site ephemerides after selecting the stars that most interest me and also giving the Shawn Dvorak´s website a try.

Maybe even the combination of the AAVSO ephemerides together with any planetary software offering perspective/observing site customizing (e.g. Starry night) could be enough and serve well for these purposes, as long as I can get an idea of wether such target stars will be reachable from my site at the specified universal times.

I also realize that, the "opposite" question will also happen, that is, there could be interesting (for me) ephemerides that are actually reachable from my site but won´t be published on AAVSO ephemerides because such stars won´t be reachable from american longitudes in that period. 

So it´s the best idea to proceed following your recommendation: a) first of all determining a set of interesting stars ("program") for this stage of my learning curve, b)confirm or discard their reachability from my site, and c) plan the possible observations.

I´m happy if this question could potentially help other beginners (like me) living away from american longitudes.

Thanks again and best regards from Spain!


Javier

AAVSO 49 Bay State Rd. Cambridge, MA 02138 aavso@aavso.org 617-354-0484