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[sarwat]

There is something wrong with the moon phase calendar. May be they are computing the phase as a linear quantity (100% in 14.5 days so 6.9 perday)


Since we see the moon as a disk and not as a globe, the projection is to be taken. Therefore, the phase
increases slowly at first and rapidly as we approach the full moon. Here is a simple formula :

1+cos(theta)
---------------- X 100
2

where theta is the phase angle. Now if we only knew how to find the phase angle ;D

An approximation would be to assume that it varies from 180 to 0 linearly in 14.5 days. This evening, the moon will be a little less than 1.5 days old, giving theta around 161 degrees. Works out to be around 2.7%

So all we need to do is memorize the cos function table and we will be on our way...

;D

Cheers,
Sarwat

[Centaur]

My highly accurate calculation has the apparent lunar disk 65.3% illuminated on 2004 SEP 22 @ 18:50 CDT as viewed topocentrically from Chicago's Adler Planetarium. Geocentrically I calculate 65.2%. On this site it reads 64.1%.

The monthly calendar here showing the daily Moon phase seems to be depicting it at an early time of the day. Possibly that time is 00:00 UT on the date for the morning that follows the evening here in Chicago.

I publish a monthly astronomical calendar on my website. It is customized for my location in Arlington Heights, IL but is suitable for anyone in North America, especially Chicagoland. The Moon is depicted as it is seen on the night between the two dates it straddles. The correct orientation of the bright limb is demonstrated. A waxing Moon is shown at the time midway between sunset and moonset. A waning Moon is shown at the time midway between moonrise and sunrise. The apparent angular diameter is shown varying from day to day. Earthshine and the oppositional flash are taken into account. Information on eclipses and planetary visibility is included.

It can be made into your background wallpaper. To see it, click:
www.curtrenz.com/astronomical.html

Then click the blue button for the monthly calendar of your choice.

Please reply here to let me know what you think of it or if you have questions.

[Chicago Astronomer - Astro Joe]

I was casually scanning the CloudyNights website the other day, and came across Centaur's post there. I had also noticed that he is a resident of the Chicagoland area, and invited Curt to come and take a look at the Chicago Astronomer Forum... after seeing his Lunar calendar.

It is well put together, and more accurate for Chicago area Lunar gazers. I have taken the liberty to display a small thumbnail here of his work:

©CurtRenz - Centaur

I like how it displays the moon between the dates as we are expected to view it...and other pertinent information.

Good job...What's the story behind it's creation Curt?

[Centaur]

Joe, thanks for the good word on my calendar. As you may guess, I am not only an amateur astronomer, but also an amateur software designer. I began similar projects about 20 years ago on a Commodore 64. Later things got more sophisticated on an Amiga 500. Then I went through a quiet period with computers, as my work with a Chicago based financial TV program took up much of my time.

In 2001 I was asked to write a book on stock market technical analysis, which would include many charts. McGraw-Hill's graphical standards required that I get a modern computer and software. So I got a Dell laptop so I could do work on the commuter train. The PoweBASIC software language was recommended by the author of a book related to celestial mechanics. I combined that with the associated Graphics Tools from PerfectSync.

When I needed a break from my book writing, my pleasure was writing astronomical software. Books such as "Astronomical Algorithms" by Jean Meeus, aid me in the calculations for my programs. While I was developing an improved version of my lunar calendar, I also became a beta tester for the next version of Graphics Tools. My calendar convinced them to include a routine for rotated ellipses which really helped with my lunar images.

Later, I added the eclipse information, like that seen on my October calendar. If you go back to my website's astronomical page you will find a more detailed graphic which depicts nine phases of the upcoming lunar eclipse.

In my post above I gave details relating to the nightly lunar images. The info on lunar phases and distances at the bottom of the calendar may require further explanation. The Perigee/Apogee times and distances are geocentric using kilometers. The phases are customized for Arlington Heights, although I can easily set them for any location. The figures beneath the images indicate the illuminated fraction of the apparent lunar disk. I do not use the simplified phase definitions that were necessary in pre-computer days, which noted the times that the geocentric differences between the ecliptical longitudes of the Moon and Sun were multiples of 90 degrees.

Until quite modern times, "New Moon" referred to the slender crescent seen a day or two after conjunction. Nowadays, most calendar makers label the day of conjunction as that of the New Moon. I use the older term "Dark Moon" and define that as the moment of minimum illumination of the apparent lunar disk as seen topocentrically from here. Similarly, I define "Full Moon" as the moment of maximum illumination.

The use of the astrological terms "first/last quarter" are confusing to people, since a Half Moon appears in the sky about those times. The quarters refer to the end of the first quarter or beginning of the last quarter of the Moon's synodic period relative to the sun, and are defined as the times of 90 degrees (quarter circle) separation in ecliptical longitude. I use the more commonly understood term "Half Moon" and define it as the moment of 50% illumination as observed topocentrically.

The information on planetary visibility was added recently. My terms are defined for an observer in Arlington Heights. I define a "Morning Star" as any planet which at sunrise is either above the western horizon or at least 10 degrees above the eastern horizon. I define an "Evening Star" as any planet which at sunset is either above the eastern horizon or at least 10 degrees above the western horizon. I define a "Midnight Star" as any planet which is above the horizon at local midnight, which is the moment midway between sunset and sunrise (the date is the evening date). It's possible for two or three of these criteria to be met on the same date. "Lost in Glare" means the planet fails to meet the other criteria and is therefore too close to the Sun to be easily seen.

My calendars obey the standard of the broadcast industry and many countries around the world: the entire weekend is placed at the end. Even in this country a growing number of calendar makers are starting to use this format. I find it more sensible.

For quite a while my calendars were customized for the location of Chicago's Adler Planetarium. If folks would like me to return to that habit or have another suggestion (or question), please let me know. Happy Viewing!

[Chicago Astronomer - Astro Joe]

Centaur,
How do you set the customization for the calendar? Is is thru lat/long?

Let's discuss this some more....I'll PM you.

[Centaur]

Joe -- basically, yes.

The program just requires 6 pieces of input:

1) Year
2) Month
3) Longitude
4) Latitude
5) Altitude above sea level
6) Time Zone

In the case of the final 4, I have dozens of locations for which I only need enter a single code number. In the case of the first two, the default is next month. The year can be any from -4000 (4001 BC) to 2799.