presents: Last revised: 06/22/02

 Astro Pal© Circumstances Calculator 

Version Notes:  1.10 - Sep 8, 2000

Astro Pal© is a browser based tool that reports local circumstances of use to the amateur astronomer.  This versions includes various time-scales for the current instance and a handy list of celestial objects riding high on the meridian.  An easy to use control panel allows customization for any time and place.

Observer Time and Place Objects Near Meridian
Local Sidereal:

Modify Data Control Panel     
Longitude: °  West  
Local Time: hr (0-23)  mn (0-59)
Local Date: Yr (2001)  Mth (1-12)   Day (1-31)

Accuracy Notes
All calculations rely on on the Date/Time properties reported by your operating system.  For high-accuracy set your system to the correct time, time-zone, and daylight-savings (summer time) status for your location.  Public domain National Institute of Standards and Technology Software that can synchronize your computer with the atomic clock is available.  Follow the above link and select the software for your computer.  (That document also contains a technical discussion of time data format that is not required to run the software.)

Usage Notes
Take Astro Pal© with you to the observing site by using the File/Save As feature on the Microsoft Internet Explorer  browser.  This will create an HTML file and an accompanying subdirectory based on page title.  You can move the file and directory to a laptop or other machine and get all the functionality of Astro Pal© without logging on.  Note that Netscape 4.08 can not save the page properly to do this.  

Another possibility is to generate print-outs of this page at various dates/times and places of interest.  Internet Explorer can limit printing to highlighted selections.  

The Observer Time and Place section reports your local time/date, Coordinated Universal Time (UTC)/date, and Local Mean Sidereal Time for your Longitude.  (Netscape users can click in the text boxes and view the complete record using arrow and [Home]/[End] keys).  For first-time users the displayed longitude is that of your time-zone meridian.  As such the sidereal time reported can be off by a half-hour.  This can be corrected through the Modify Data Control Panel described below.

Due to time-zone differences the UTC on an event happens at differing local dates and times around the world.  Use the data in this section to confirm your UTC date and time of observation.  Local sidereal time indicates what meridian of Right Ascension is currently above your observing location.  This can be used for star map orientation.  The longitude, in decimal form, indicates the terrestrial meridian the calculated values are valid for.

Objects Near Meridian lists objects approaching or just past their highest point in the sky.  Listed are setting circle calibration stars -- a list of bright easy-to-find stars used to confirm your telescopes positioning accuracy.  (First polar align your telescope according to the manual.) To calibrate manual telescope setting circles just point at one of these stars and then dial the RA circle to the listed coordinates.  Point at the other stars and confirm their positions.  Hint: some telescopes have inner and outer (north and south hemisphere) RA scales; this exercise will help you sort out which scale to use if you are new to this.  

A short list of some of the most easy-to-see Messier Objects near the meridian is included.  This is a nice feature for beginners just learning the sky.  Where possible "show-case" objects are featured that are suitably impressive enough for viewing by non-amateurs.  Show them these targets while you wait for your scope to cool-down before your serious observing session.

The Modify Data Control Panel is highlight in blue.  Customize the data displayed in the prior sections through this.  Enter your correct Longitude in degrees, minutes, and east/west of the prime meridian.  You can enter decimal values for minutes to account for seconds, i.e., 5.1667 minutes is 5' 10".  Similarly enter local time and date in the indicated places.  Do not enter negative signs, non-numeric values, and numbers that exceed the indicated range.  Negative will be treated in the absolute value while the rest will be ignored. Press the [Save] button to recalculate and display the new circumstances.  Note that a cookie with the entered longitude will be placed on your computer.  This is to avoid having to set your longitude each time your return to Astro Pal.

Send comments concerning Astro Pal.  What features would you like to see?  Did you get an error?  or have a layout problems?  

Related Links
These links will open pages with related content.  Note that the listed Astro Utilities pages are the static demo HTML version and will not carry-out live calculations.  Also visit the Astro Computing section of this website.

Astro Utilities: Julian & Gregorian Calendars
Notes on the civil calendar.
World Time Zone map
Global lettered time zones.
Eagle Geocoding: Street Level
USA longitude/latitude.
Astro Utilities: Universal Time
Astro Utilities: Sidereal Time Conversion 
Notes on sidereal time calculations.
World longitude/latitude.

Terms of Use
The SOFTWARE PRODUCT was designed for hobby, educational, and entertainment purposes only.  It should not be used for mission critical or commercial applications. The user accepts the responsibility to investigate the suitability and adaptability of this SOFTWARE PRODUCT for their own purposes. This SOFTWARE PRODUCT is not warrant to be error free. In no event shall the author of this SOFTWARE PRODUCT be liable to you for any consequential, special, incidental or indirect damages of any kind arising out of the delivery, performance or use of the software, even if the author has been advised of the possibility of such damages. The information in this SOFTWARE PRODUCT and any accompanying documents is subject to revision without notice, and represents no commitment to you the user.

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