Enhanced the Time class to correctly calculate calendar
dates for the year range -999999 to +999999.
Made unit tests in C, C#, and Kotlin all exercise
the full year range, for February 28 and March 1 in each year,
to make sure we cover before and after each potential leap day.
Fixed problems converting AstroTime to calendar dates and back.
Also expose struct CalendarDateTime to outside callers,
for convenience dealing with Gregorian calendar dates.
Implemented and added tests for the following methods:
AstroTime.TryParse()
AstroVector.TryParse()
I still need to implement StateVector.TryParse().
Fixed a bug in CalendarDateTime: the NOVAS cal_date
function worked well, except when years go below
somewhere near -12000. Then the formulas start making
negative numbers, which messes up the calculation
of the month and day.
So to fix this, I figured out that any multiple of
400 years added to any calendar date gives the exact
same calendar date. And 400 years always has the exact
same number of days in it: 146097.
Because one million years = 400 * 2500 years, I can
add 2500*146097 days at the front of the formula
and subtract 1000000 years at the back, and everything
works for the entire range of years plus or minus
one million years from the present.
Because my date format allows for no more than a 6-digit
decimal year, this is perfectly adequate.
Contributor @ris-tip ran into erroneous test failures
due to tiny floating point calculation differences.
I'm adjusting the thresholds slightly so his tests will pass.
Added EclipticGeoMoon as output to the temp/*_check.txt files as 'm' lines.
This ensures that all the languages calculate nearly identical values.
Optimized EclipticGeoMoon a little more by eliminating a redundant
call to mean_obliq.
While trying to convert ecliptic coordinates from mean
equinox of date to true equinox of date, I ran into excessive
overhead from the IAU2000B nutation model. The fact that it
uses 77 trigonometric terms made the calculations a lot slower.
https://apps.dtic.mil/sti/pdfs/AD1112517.pdf
Page 4 in the above document mentions a shorter series
“NOD version 2” that has 13 terms instead of 77 as used in IAU2000B.
I had not noticed NOD2 before, because it appears only in
the FORTRAN version of NOVAS 3.x, not the C version.
After reading the FORTRAN code, I realized NOD2 is the same
as IAU2000B, only it keeps the first 13 of 77 terms.
The terms are already arranged in descending order of
significance, so it is easy to truncate the series.
Based on this discovery, I realized I could achieve all of
the required accuracy needed for Astronomy Engine by
keeping only the first 5 terms of the nutation series.
This tremendously speeds up nutation calculations while
sacrificing only a couple of arcseconds of accuracy.
It also makes the minified JavaScript code smaller:
Before: 119500 bytes.
After: 116653 bytes.
So that's what I did here. Most of the work was updating
unit tests for accepting slightly different calculation
results.
The nutation formula change did trigger detection of a
lurking bug in the inverse_terra functions, which convert
a geocentric vector into latitude, longitude, and elevation
(i.e. an Observer object). The Newton's Method loop in
this function was not always converging, resulting in
an infinite loop. I fixed that by increasing the
convergence threshold and throwing an exception
if the loop iterates more than 10 times.
I also fixed a couple of bugs in the `demotest` scripts.
Added Python support for user-defined stars.
Defined new StateVector methods: Position and Velocity.
Defined division operator: Vector / float.
Bumped version number to 2.1.12.
The C# version of the altitude searches now work correctly
near the Earth's poles. This is a port of the C version.
Cleaned up a little code in the C version.
The .NET type System.DateTime is limited to the years 0000..9999.
The Astronomy Engine type AstroTime was using System.DateTime to
convert a (year, month, day, hour, minute, second) tuple into a
fractional day value. This caused an exception for years outside
the supported range 0000..9999.
I ported the NOVAS C 3.1 functions julian_date and cal_date to C#,
and removed the dependence on System.DateTime.
Now we can create AstroTime for a much wider range of year values.
Allow converting AstroTime to string for years before 0 and after 9999.
In the unit tests for searching forward and backward
for moon phases, in addition to new moons, also test
first quarter, full moon, and third quarter.
Verify that forward and backward searches work for
100 start times between a single pair of consecutive events.
The following Python functions now support searching
in forward or reverse chronological order:
SearchRiseSet
SearchAltitude
SearchHourAngle
Made some minor performance improvements to the
other implementations: return sooner if we
go past time window.
The following C# functions now support searching
in forward or reverse chronological order:
Astronomy.SearchRiseSet
Astronomy.SearchAltitude
Astronomy.SearchHourAngle
Also fixed places where I forgot to update documentation
for the corresponding changes to the C code.
Enhanced the Kotlin function searchMoonPhase
to allow searching forward in time when the `limitDays`
argument is positive, or backward in time when `limitDays`
is negative.
Added unit test "moon_reverse" to verify this new feature.
Enhanced the C# function Astronomy.SearchMoonPhase
to allow searching forward in time when the `limitDays`
argument is positive, or backward in time when `limitDays`
is negative.
Added unit test "moon_reverse" to verify this new feature.
It makes more sense to report Jupiter's moons with
individually named structure fields rather than an array.
It reduces the overall code and documentation size,
and outside of unit testing, there are few cases
where iterating over an array of moons is more
lucid than using the names of the moons.
This is a breaking change, but hopefully very few
developers are using this function yet.
Fixing the breakage is very simple.
Added functions:
searchPlanetApsis
nextPlanetApsis
I discovered that I had an unnecessary special relaxation
of apsis error tolerance for Pluto. It turns out that currently
0.1 degrees of orbital rotation is enough for all the planets.
Search for times when the Moon ascends or descends
through the ecliptic plane. These are called
ascending and descending nodes. Added the functions:
searchMoonNode
nextMoonNode
Also corrected comments in the unit tests that
incorrectly stated nodes occur when the ecliptic
longitude is zero. They should have said the
ecliptic latitude is zero.
The existing lunar libration functions in the
other languages (C, C#, Python, JavaScript) were
calculating the Moon's ecliptic latitude and longitude
in radians, not degrees as intended. They have been fixed.
Implemented the libration function for Kotlin.
Implemented the `illumination` function, which calculates
visual magnitude, illuminated phase angle/fraction, and
ring tilt for Saturn.
Implemented `searchPeakMagnitude` for finding when
Venus appears brightest in the sky.
