The calendar below shows the phase of the moon for each day of the selected month. You can change the month and year to whatever you like between January 3999 BC and December 3999 AD.
Hovering your mouse over any day in the calendar will display a popup showing the moon's distance, phase and other information.
Instructions on what the various controls do is found below. There is also a reference section for those interested in the algorithms used.
Feel free to with your thoughts on the program.
Ultimately, written instructions should be unnecessary; it ought to be intuitively obvious how to use the software.
Until then:
New - A second full moon which occurs in a single month is called a blue moon. The program now recognizes when this occurs and tints the corresponding drawing blue. See May or June 2007 for an example. Which month depends on what time zone you are in; the last full moon in May occurs near midnight UTC, and may be translated into Thursday, May 31 or Friday, June 1 when converted into local time. May contains a blue moon for most of North and South America, while June has one for much of Europe, Asia and the Middle East.
Note that this definition, though common, is historically incorrect. See this article on the history of the phrase “blue moon”. Although the history behind the phrase is fascinating, the common usage is now so prevalent that it is the one adopted in the program.
New - The Settings... dialog now allows you to save your settings; the next time you visit, any settings you saved will be restored. The dialog now has Cancel, Apply and Save buttons on the bottom. Cancel will cancel any changes made to the dialog that haven't been applied or saved; Apply will apply any changes made to the displayed calendar, without saving them; Save will apply any changes and save them for use the next time you visit.
Note that this is a Java program; your browser must be set to allow such programs to run. Check your browser Preferences or Settings to ensure that Java is enabled if you cannot see the calendar at all.
This version of the calendar requires Java version 1.5 or greater, which Sun Microsystems confusingly refers to as either version 1.5.x or version 5.0; if you have an earlier version, Windows will detect this and automatically download and install the correct version. On other systems, you will be directed to the download page for the required version, where you will find instructions on how to download and install Java on your system.
The month, year and era (AD or BC) can be changed by clicking on the appropriate field, or portion of it, and selecting a new value.
Hovering your cursor over any day of the month will pop up a ToolTip box displaying specific information about the moon on that day. Note that the ToolTip will disappear after a few seconds; you can keep it showing by moving the mouse slightly within the day of interest.
At any time, the displayed month can be changed back to the present month by clicking the Reset to Current Date button.
Clicking on the days - they're buttons - doesn't do anything but make them go in and out. Someday, clicking on them will do something really cool. But not today.
The "Settings..." button will bring up a separate window containing various controls, discussed below. Note that on some platforms and browsers, this window will sometimes be hidden by the main browser window. If you click the "Settings..." button and nothing happens, try looking behind the browser window for the Settings dialog.
The calendar does not currently calculate the times of moonrise or moonset. If you need these, the US Naval Observatory provides a page where you can generate these times for an entire year.
The Position Angle is the angle which a line drawn between the cusps of the terminator makes with true north; it is NOT the angle made with the zenith, which is called the Zenith Angle, and which is dependent on both location and local time. The Position Angle can be turned on or off; if off, the line between the cusps of the terminator is always drawn straight up and down.
Distance Scaling scales the drawings of the moon depending on the moon's distance at the moment the phases are calculated; the default of 1 alters the size based on actual distance, while greater values raise the scaling to the second, third or fourth power, respectively. Turning this control Off makes all drawings the same size.
Most people in the northern hemisphere see the moon toward the south, and therefore orient it with north up. In the southern hemisphere, south is up, and the appearance of the moon is "flipped" with respect to it's northern hemisphere appearance. The Orientation setting lets you control which view is used.
The Phase Times setting selects whether the phases should be calculated at the current instant of Local Time, at Local Midnight, or at UTC Midnight. UTC corresponds to Greenwich time, and is commonly used in astronomical references.
Note that the canonical phases (Full, New, First and Last Quarter) are calculated and shown at the precise instant the particular phase occurs. This may make the preceding and subsequent phases look slightly off, depending on the time at which the true phase occurs.
The Language that some items are displayed in may be selected. This only affects the month, era, weekdays and similar fields in the ToolTip displays. Basically, I get these for free; internationalizing the entire application would require actual work.
Note that not all languages are available on all systems. The ones shown all display properly (I guess - who knows what they really say?) on my Linux system; under Windows, the Asian and Arabic fonts may or may not be recognized, and may or may not have an entry; if they do have an entry in English only, they will probably not display properly. This probably varies from system to system; sometimes, adding Asian languages through the Windows Control Panel will add the Asian fonts, or they may already be installed.
The First Day of Week may be set to whatever day is selected; in Europe, calendars are commonly printed using Monday as the first day of the week instead of Sunday, and as long as I was coding that I figured I might as well generalize it. If the program determines that your computer is set up to use such a convention, the calendar will already use whatever the first day of the week is for your locale.
The Language and First Day of Week settings should automatically detect the values your computer is set for, and the Moon Calendar should display using these default settings. For example, a computer loading the applet in France should display the calendar using French as the language, and using Monday as the first day of the week. As near as I am able to simulate such things, they seem to work; extensive global travel, however, is not in my budget at the moment, and I don't know what actually happens when the applet is loaded in foreign countries. Feedback on this is most welcome.
The original Moon Calendar program, which I wrote over ten years ago, has had a long run. But recent changes to Java have made it effectively unrunnable on modern machines. The version on this page solves that problem, and adds features such as high quality rendering and direct printing that were unavailable in the older version. If, for some reason, you still want to use the older version, it remains available here for the foreseeable future.