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Q: I found a sunrise/sunset time on another web site, TV or the newspaper and it is different from the one here by an hour. What is the difference and which one is correct?
A: All times shown on this Web site are adjusted to daylight saving time using the algorithms
here. The calendar will have the phrase "DST is in effect for the entire month" if that is the case, if it transitions to or from daylight saving time during the month the day will have "DST Begins" or "DST Ends". If the time for that month is Standard or Winter time it will state that.
You do not need to add an hour to any times, unless the time shown is standard time and you know that the location will be observing daylight saving time then. If this is the case add one hour to the times.
The Windows Sunrise Sunset Calculator (Sun.exe) gets its setting of daylight saving time from Windows operating system. If your Windows clock adjusts properly, then the calculator will use the new setting.
Q: I found a sunrise/sunset time on another Web site or the newspaper and it is different from the one here by a minute or so. Why are they different?
A: Please read the Accuracy Statement.
Q: Has this Web Site and the 'System Tray' application (Sun.exe) been updated for the new 2007 Daylight Saving Time changes for U.S.A. and Canada rules, and any other countries?
A: The Sun.exe application, the 'System Tray' appilcation, asks Windows for your current DST setting, so if your Windows 95/98/2000/XP setting is okay then the Sun.exe times should be correct. You may need to reboot your computer or stop and restart Sun.exe if the DST has changed recently.
The Web site uses http://www.sunrisesunset.com/dst_info.html for all DST adjustments.
Q: I clicked on Sun.exe or the 'zipped version', but nothing happened. What do I do?
A: The program will place an icon in the Sys-Tray, this is the icon area near the clock in the Task Bar. If you have the Task Bar on auto-hide you will need to mouse to it to see the new icon. When you reboot the computer, the Sun icon will not be there unless you put it in your StartUp folder, see the next question to find out how to do this.
Q: I would like the Sun program to start up automatically, how do I do this?
A: Wherever you have the "Sun.exe" file, right-click on it and select "Cut".
Right-click on the "Start" button (with the little Flying Windows Flag icon) and choose "Explore". Open the "Programs" folder under the "Start Menu" icon and select the "StartUp" icon. Right-click on "StartUp" and select "Paste". The "Sun.exe" file should now be in the "StartUp" folder (look in the right pane) and it will start each time you boot your computer.
Q: Is there any way to save more than one custom location in the Sun.exe program?
A: Not through the program, but if you don't mind editing the Windows registry you can adjust the city lists.
Start the registry editor (Start button, Run..., type regedit, click OK) and navigate to HKEY_LOCAL_MACHINE \ Software \ SunriseSunset.com \ Sunrise-Sunset \ ver 1.0 \ Cities. You will find four entries there, choose the folder icon of the list you wish to edit (don't choose Custom, see below) and the cities will appear in the right pane. To add a new city, select Edit from the menu, then New, then String Value. A new item will appear in the list in the right pane, simply type the name of your new city and press enter. You now need to give it the lat/long information, double-click on your new city and in the dialog box enter the latitude, a comma, the longitude, a comma, the time zone number, and a comma then a 1.
The time zone number is -5 for Eastern, -6 for Central, -7 for Mountain and -8 for Pacific. Latitude is positive for west of GMT, negative for east, longitude is postive for north and negative for south. Both numbers should be entered as decimal number with an optional decimal point.
Your new city will show up in the list the next time the Sun program is started, but it may not be in sorted order, just search the list and you will find it. A simple way to search the list is by pressing the first letter of your city until it shows up.
Don't enter too many new cities, the program can only handle 200 total. The number of cities it comes with automatically is 133: 76 U.S., 14 Canadian, 42 international and 1 custom, so unless you delete any of the original cities, you can add 67 of your own.
Note: The program will only read in the first custom city, no matter how many are entered in that folder, so just leave the Custom folder alone.
Q: I was wondering if you could make the sunrise/sunset times available for the Palm Pilot computer?
A: I currently use Astro Info, which I downloaded a few years ago, but I'm not sure it's available now. In any case, I do not intend to adapt my sunrise/sunset program to the Palm Pilot.
Q: Do you have a Mac version of the Windows Sunrise Sunset Calculator?
A: No, but you can use this site for calendars.
Q: Do you know of anything that I could put on my toolbar regarding moonrise and moonset times along with phases of the moon?
A: Here is what I use: Lunabar
Q: I was wondering if you will be adding high and low tides for ocean-side cities?
A: I won't be adding tide
information, it is just too complicated, and besides there is nice program available for free that does tides. You can find it at WXTide32.
Q: What is the definition of sunrise and sunset? Is it the time when the leading or trailing edge or the center of the sun passes the horizon?
A: Generally speaking, the definition is when the leading or trailing edge of
the sun passes the horizon. This time is somewhat different from the more
specific definition which is called the geometric rise or set. The
geometric rise or set of a celestial body is when the center of the object
passes the horizon and there is no atmospheric refraction (i.e. there is no
atmosphere). Of course, here on Earth we have an atmosphere which actually
bends light down toward the surface when the object is near the horizon,
allowing us to see the sun (and the moon and stars) before they would
normally be visible if there were no atmosphere. And as for the center of
the object, if you have ever watched a sunrise or sunset, you will know that
it takes 3 to 4 minutes at most latitudes once the sun touches the horizon
to when it doesn't because the sun has a large diameter compared to other
stars which appear as points, thus actual sunrise or sunset is actually
about 1 1/2 minutes before or after when the center of the sun is at the
horizon.
The algorithms used on this site take the atmospheric refraction and the diameter of
the sun into account so the times should be accurate to the leading or
trailing edge passing the horizon.
Q: I see that March 18 has exactly 12 hours of daylight for the place where I live. I thought that the equinox was March 21 (or September 22). What is the exact definition of the equinox and when does it occur?
A: From Webster's Dictionary comes the first
part of the answer.
Equinox: The time when the sun crosses the plane of the earth's equator,
making night and day of equal length all over the earth and occurring about
March 21 (vernal equinox) and September 22 (autumnal equinox).
Well, I checked one of my astronomy books (Stars and Planets by Peterson
Field Guides) and found out that the dictionary was right up to a point.
The sun crossing the plane of the earth's equator was correct but the length
of day and night being equal is not correct. Here is the explanation:
"Although day and night are theoretically equal in length on the days of the
equinoxes, that would be true only if the sun were a point, not a disk, and
if the earth's atmosphere did not bend sunlight. However, the top of the
sun actually rises a few minutes before the center of the sun's disk--the
point used in calculations. Also, the earth's atmosphere bends sunlight, so
we can see the sun for several minutes before the time sunrise would occur
and after the time sunset would occur if the earth had no atmosphere."
Q: What elevation is used to calculate the times?
A: The elevation is always calculated at sea level. Mountains and other large landmarks may also affect local times, these are not accounted for in the times presented on this Web site or the Windows Sunrise Sunset Calculator.
Q: Can you send me the algorithms you used to calculate sunrise and sunset?
A: No, but you can search the Internet and find code that others have made available. Try
Online Calculators and
Sky & Telescope -- follow the Resources link.
I got my algorithms from a book, "Astronomical Algorithms" by Jean Meeus, ISBN 0-943396-35-2, published by Willmann-Bell Inc.
He also has a book "Astronomical Formula for Calculators" that is probably better for programmers.
You can order them at a real bookstore or online.
Q: I've got a question you didn't cover. Where else can I look?
A: Many other answers to questions can be found at the following sites: