App/webpage to calculate meridian hour angle at various twilight times?

[cathalferris]

I ask this here in the hope that someone else has already done or knows where to do this this before I go and try to calculate it out myself..

To try and solve a problem that I've been thinking of over the past few years, I would like to be able to tabulate the local sidereal time, for various twilight timings throughout the year, for various latitudes.

I want to find out if it is possible to observe items that were lost in the twilight e.g. in July, that will become more visible with the shorter and sooner twilights a month later. Algorithmically, it's the local sidereal time of twilight, and I should be able to graph it to show if there's better visibility of stuff when the days get shorter.

I can find many calculators for twilight times, but nothing that makes it easy to stick into a spreadsheet for graphing. I can use Calsky for the values but it's a monumental effort to reduce the data produced. I have xEphem but I can't yet figure out how to calculate what I need in there.

(unless I'm missing something really simple and obvious..)

[m.tweedy]

don't fully understand (but that's my problem) 

will this help

http://www.pierpaoloricci.it/download/downloadsoftware_eng.htm

maybe under time?

[m.tweedy]

http://aa.usno.navy.mil/data/docs/siderealtime.php

http://www.umich.edu/~lowbrows/links/

hope there is something that helps

[CharlesW]

The USNO's app here Rise/Set/Transit Times for Major Solar System Bodies and Bright Stars outputs to table format. You could copy paste the results into Notepad to hopefully put it in a format, tab delimited, that Excel likes, and then import it as a tab delimited text file. Then I think you could play with the data to your heart's desire.

[JRWASTRO]

Re:  ...  I would like to be able to tabulate the local sidereal time, for various twilight timings throughout the year, for various latitudes ...

And

Re: ...  the local sidereal time of twilight ...

1. There are 3 twilights viz.

Civil Twilight ,Nautical Twilight and Astronomical Twilight

Astronomical twilight is when the sun is 18 degrees below the horizon

and darkness is considered to be total ... you can start imaging and observing!!

Nautical Twilight is when the sun is 12 degrees below the horizon .

You can see the navigation stars and the horizon at sea so you can take your fix for the evening

Civil Twilight is when the sun is 6 degrees below the horizon ... switch on your car lights and watchout in case you hit a roo !!

OK.

We now need to calculate sunrise and sunset. This is easily done. I have coded these in MATLAB and you are welcome to have the code.

Twilight times are simple offsets from the rise and set times for the sun.

You will need to calculate Local Mean Sidereal Time (LMST) from the times of twilight and dates .  I have coded the calcs for LMST to run on my HP50G calculator. You are welcome to have this code also.

Jeremy.

[michael8554]

Not software, and only 50N, but these almanacs come free once a year with an issue of Sky & Telescope

http://www.shopatsky.com/product/skygazers-almanac-2014-50-deg-n/calendars-and-almanacs

Shows evening and morning twilight, planet rise, culmination, transit, and set times, moon phases etc etc

Michael

[cathalferris]

Just to provide closure on this, I've found a neat workaround that gets me the exact information I wanted, reasonably easily.

In Cartes du Ciel / Skychart, on the File menu, select "Calendar". Choose a range of dates you want to examine. If asteroids need to be calculated it'll do that. Eventually you'll be presented with a table of dates and times. Selecting the Twilight tab, you can double-click any of the times and you'll see that the main map window is now set for that time. The same applies for pretty much any of the items listed in the tables in the tabs.

I can step through the table and get a visual representation of what I was looking for. Yes, there is a week in late July when objects are higher in the west each night at astronomical twilight, and that the rate of descent of the summer stars into the west is slowed given the earlier time of astronomical twilight ending each evening helps offset the 2hr of RA change a month .