last updated February 2020

Solpage is a software program that computes planetary positions, angles and alignments for a given date or time-frame. In order to accurately compute the positions of the planets Solpage uses the periodic terms as provided by the VSOP87 solution.


Development of the program by Frank Hoogerbeets started in February 2016. Initially only the alignment computation engine was developed. This engine computes the exact time when two celestial bodies reach the same longitude relative to a third celestial body. Throughout 2016 this engine was corrected and optimized to handle 8 decimal digits precision.

In October of the same year the listing of positions and angles for a given time and centric view was added.

In November new features were added, the most important of which was the possibility to lookup combinations of different angles in a given time-frame.

In July and August 2017 the Solar System Geometry Index (SSGI) algorithm was added in an attempt to increase the accuracy of earthquake forecasts. This algorithm was revised and extended several times in the following two years.

In February 2020 Solpage reached version 6. Some code was optimized. Several options were added to make the program more convenient to use and to allow for more selective data to be generated. In total the program consists of some 6000 lines of code, not counting the user interface or the VSOP87 data tables.

With the release of version 7 in September 2020, Lunar sub-geometry (LSG) was added both to the angles tab as well as the SSGI algorithm. Some experimental options, such as wide planetary geometry (WPG) were added in subsequent minor versions during 2020 and 2021.

As of version 7.4, which was released in September 2021, the SSGI planetary geometry (PG) algorithm was categorized into Mercury-specific (PGme), Venus-specific (PGve) and general planetary geometry (PG). This way the resulting SSGI graphs make directly visible which geometry is predominant.

While most planetary computation software is limited to heliocentric and geocentric positions, Solpage is unique in that it supports any centric view. It was one of the main reasons for starting the Solpage project.


As an example we ask Solpage when Jupiter, Uranus and Neptune will be in exact alignments between 1 January 2000 and 31 December 2199. With a Jupitercentric search, the program finds one match:

2167-02-08, 22:03:59 301°21'55"

So according to Solpage the next time Uranus and Neptune are aligned as seen from Jupiter is on 8 February 2167 at 22:03:59 UTC, when the longitude of both planets reach 301°21'55". Below is a screenshot taken from Solar System Scope depicting the planetary positions on 8 February 2167 at 22:03 with the alignment marked by the yellow line.

Jupiter-Uranus-Neptune alignment 8 February 2167

A rare alignment of Jupiter, Uranus and Neptune, 8 February 2167

The computation of the above example was done on Manjaro Linux 17.1.11 using an Intel Core 2 Quad Q9550 2.83GHz processor. It took Solpage about 5 seconds to scan 200 years and display the result.


Ditrianum is the sole owner and developer of Solpage, which is used to research and forecast larger seismic activity. The program is not available for download or commercial use.

Solpage is unique in that it supports all centric views.
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