Rotation of Moon inexact

Bug #499971 reported by Dave Chapman on 2009-12-23
32
This bug affects 3 people
Affects Status Importance Assigned to Milestone
Stellarium
Medium
gzotti

Bug Description

When simulating Moon phase in millennia far in the past or future (say 2000 years), the face of the Moon is rotated East or West, respectively, relative to its tidally locked orientation. For example, when simulating the Venus-Jupiter conjunction of -1 June 17, the Moon is rotated about 40 degrees East so that Mare Crisium is totally hidden behind the limb. I have found the same bug in other programs, but not all.

2009-12-23T17:31:30
/Applications/Stellarium/Stellarium.app/Contents/MacOS/stellarium -psn_0_712878
Mac OS X 10.5
Compiled with GCC 4.0.1
Qt runtime version: 4.5.0
Qt compilation version: 4.5.0
Addressing mode: 32-bit
You look like a Mac user. How would you like to write some system info code here? That would help a lot.
 -------------------------------------------------------
[ This is Stellarium 0.10.2 - http://www.stellarium.org ]
[ Copyright (C) 2000-2009 Fabien Chereau et al ]
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Writing log file to: "/Users/test/Library/Preferences/Stellarium/log.txt"
File search paths:
  0 . "/Users/test/Library/Preferences/Stellarium"
  1 . "/Applications/Stellarium/Stellarium.app/Contents/Resources"
Config file is: "/Users/test/Library/Preferences/Stellarium/config.ini"
Cache directory is: "/Users/test/Library/Cachesstellarium"
Sky language is "en_CA"
Application language is "en_CA"
Loading Solar System data ...
Loaded 38 / 38 planet orbits
Loading star data ...
Loading "stars_0_0v0_1.cat": byteswap 0_0v0_1; 5013
Loading "stars_1_0v0_1.cat": byteswap 1_0v0_1; 21999
Loading "stars_2_0v0_1.cat": byteswap 2_0v0_1; 151416
Loading "stars_3_1v0_0.cat": byteswap 3_1v0_0; 434064
Finished loading star catalogue data, max_geodesic_level: 3
navigation/preset_sky_time is a double - treating as jday: 2.45151e+06
Loaded 10051 / 13226 NGC records
Loading NGC name data ...
Loaded 222 / 222 NGC name records successfully
Loaded 88 / 88 constellation records successfully for culture "western"
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Loaded 89 / 89 constellation names
Loading constellation boundary data ...
Loaded 782 constellation boundary segments
Loading star names from "/Applications/Stellarium/Stellarium.app/Contents/Resources/skycultures/western/star_names.fab"
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Loading star names from "/Applications/Stellarium/Stellarium.app/Contents/Resources/stars/default/name.fab"
Loaded 3215 / 4359 scientific star names
Creating GUI ...
QAbstractSocket::connectToHost() called when already connecting/connected to "simbad.u-strasbg.fr"

gzotti (georg-zotti) wrote :

Hi!

It seems the lunar rotation is modelled too simple. It also appears to show a polar libration, i.e., it swings considerably in selenographic latitude. Is the lunar body in a false reference system?

As preliminary fix for rotation, find the file Stellarium/data/ssystem.ini (on Mac, I guess it's in the Stellarium.app folder) and in section [moon], change

rot_periode = 655.7181

or some other slightly smaller value. This is no complete bugfix, beware, it just keeps the moon facing the earth well into the 4th millennium BC. The "polar swing" is not solved by this. More accurate libration formulae could be found in the literature.

Also, if Earth's rotation is really only taken from the data in ssystem.ini, this seems not to be enough for simulating long-time effects. (But I did not read enough code so far.)

Regards,
Georg

Changed in stellarium:
importance: Undecided → Wishlist
status: New → Confirmed
Dave Chapman (dave-chapman) wrote :

Libration in longitude and latitude of up to about 9 degrees is about right. They have independent causes: latitude is simply due to the tilt of the Moon's orbit, which takes it above and below the equator; longitude is dues to inconstant motion along the eccentric orbit. I will try the rotations speed fix.

tags: added: solar-system
Nick Fedoseev (nick-ut2uz) wrote :

Just a note.
The difference between real occultation of Aldebaran and simulated by Stellarium is ~35 seconds. Seems to be too high.

gzotti (georg-zotti) wrote :

Nick this is a position error I added in https://bugs.launchpad.net/stellarium/+bug/1509659. This bug here is about rotation, but yes, position and physical ephemeris must be worked over.

gzotti (georg-zotti) on 2016-09-04
Changed in stellarium:
assignee: nobody → gzotti (georg-zotti)
milestone: none → 1.0.0
gzotti (georg-zotti) on 2017-05-14
tags: added: moon
gzotti (georg-zotti) on 2017-10-01
Changed in stellarium:
importance: Wishlist → Medium
status: Confirmed → In Progress
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