Moonchaser History

Being There

Lick Observatory sits atop Mount Hamilton, East of San Jose California, and Silicon Valley. It dominates the horizon to the east and is visible from much of the bay side of the San Francisco peninsula. Since the mountain is to the East, and the moon rises in the East, it seemed that it would be an easy thing to take a picture of the moon rising behind the observatory.

It was not...

With a working knowledge of neither astronomy nor cartography, it took the author and his son nearly two years to capture the first shots of that elusive moonrise. It was only after writing the first version of Moonchaser that we succeeded. In the process we learned a lot about both topics, and spent many enjoyable evenings chasing that first much-prized photograph. More than a quarter of a century later, there is still an indescribable satisfaction in being there when the rim of the moon first peeks over the horizon in precisely the predicted spot.


The original version of Moonchaser was written for the Radio Shack TRS-80 PC-3 "pocket computer" in 1987. Despite the name, the PC-3 was really a programmable calculator, a rebranded version of the Sharp PC-1250. It featured a 24 character LCD display, BASIC in 24K bytes of ROM and 2.2K bytes of RAM for main system memory. Of that, a whopping 1,438 bytes was available for program and data storage. The optional thermal printer provided output on 2-inch paper tape, and included a cassette-tape interface that permitted programs to be stored off-line.

Moonchaser 2

Version 2 was written for the somewhat more capable Radio Shack PC-6 pocket computer. This was a rebranded Casio FX-790P which had a reasonably compatible BASIC in ROM and expanded RAM with 7,520 bytes available for program and data storage.

This photograph of the moonrise behind Lick Observatory took third prize in the landscape division of the photo competition at the Santa Clara County Fair in 1991, the year after it was taken. One of the judges remarked after the competition that they were uncertain whether or not it had been "faked" with Photoshop which was just then beginning to become popular.

Moonchaser 3

The introduction of the Apple Powerbook 140 in 1991 with 4 Megabytes of RAM and both a hard disk and a floppy drive in a portable, battery powered package proved the impetus for Moonchaser Version 3 which was a minimal rewrite of the calculator-based version.

Moonchaser 4

Peter Duffett-Smith's Astronomy with Your Personal Computer provided the astronomical code base for Version 4, a ground-up rewrite of the program. This version also ran on the Powerbook.

Moonchaser on the Web

After lying dormant for several years, Version 5 of the Moonchaser program was rewritten in the summer of 2000 as a WinCGI application to run under O'Reilly's WebSite Pro web server. The availability of wireless internet services such as Metricom's Ricochet service meant that all of the resources of the net were available in the field (This was well before any real internet connectivity was generally available from wireless phone carriers). Making Moonchaser a web application not only provided a convenient way to use the program, but made it easy to share with other photographers as well.

Moonchaser 6

Version 6 went live in November of 2000. The spherical earth model used for UTM to Lat/Long conversions was replaced with routines rewritten in VB based on Chuck Gantz's C++ program. This substantially improved precision, and supports 27 different commonly used mapping ellipsoids. Links to show the camera and target positions using the MapTech MapServer were also added. The MapTech Mapserver predated Google Maps by several years. This made it possible to shoot a moonrise without the need for paper maps, and without the use of a portable GPS.

Moonchaser 7

In May of 2011, Moonchaser was recompiled for the first time in more than a decade. The reference ellipsoid was changed from NADS 1927 to WGS 84 to accommodate switching to Google Maps from the MapTech MapServer. A new data entry screen was added to support direct decimal latitude and longitude position input in addition to the old Universal Transverse Mercator input format. Even in it's day, version 7 was an anachronism which ran on a VirtualBox Windows 2000 virtual machine, as a Visual Basic CGI on the even then unavailable O'Reilly WebSite Pro web server. All of this running on Macintosh hardware.

Current Status

The Moonchaser Calculator is currently off-line. We are in the middle of yet another total re-write. This time built around Don Cross' Astronomy.js library. The intent is to make a mobile friendly HTML5/Javascript calculator that will take advantage of the location APIs now available in Javascript.

Why Not Just Use Photoshop?

Since the Moonchaser project started, digital photography and digital editing tools such as Adobe Photoshop have blossomed. The cut-and-paste image manipulation capabilities of these products make it easy to produce a fake moonrise behind a photo of any landmark. Wouldn't that be a lot less trouble?

Yes, but... As it says on the Harley-Davidson T-Shirt, "If we have to explain, you wouldn't understand".