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I N S T R U C T I O N S F O R
U S E
You are now on the page of calculation of the ephemerides.
You will find below the different types of ephemerides
with their options:
- Ephemerides tabulated with a constant time step
- Ephemerides for a given series of dates allowing the calculation of (O-C) if data are provided
- Graphical representation of the satellite configurations for each planetary system
- Phenomena of the satellites
- Special ephemerides
The calculations use the same basis for the modeling of satellite
motion and differ only in the way in which input data
are entered and results are displayed.
Using the different ephemerides is similar for each one.
Ephemerides tabulated with a constant time step.
Ephemerides for a given series of dates
allowing the calculation of (O-C) if data are provided.
Selecting your input choices:
- In both cases
- the dynamical model of satellite motion to be used for the calculations
- the satellite for which the ephemeris is required.
- the celestial body relative to which the ephemeris will be calculated.
This may be another satellite or the center of the planet.
If you select "Earth equatorial", the satellite's "absolute" coordinates, right ascension and declination,
will be calculated.
Note that it is also possible to calculate the position
of the center of mass of the system relatively
to the center of mass of the planet.
- the ephemeris for the planet: if absolute coordinates RA, DEC
of the satellite are required, this choice is significant
since errors on coordinates of the planet are completely
included into the errors on the satellite positions.
When calculating satellite relative coordinates,
the influence of this choise is very small.
- the observing site for which topocentric coordinates
must be calculated. The IAU number of the observatory
must be entered manually. To find out the number,
use the corresponding list proposed through a link.
If the number is 500, the satellite's geocentric coordinates
will be calculated.
- the epoch of equator and equinox of the reference frame.
The choise of Mean of Jan 1st means the selection of the mean coordinate
system of the beginning of the year to which belong the ephemerides dates.
- the time scale of ephemerides (TT: Terrestrial Time formerly Ephemerides Time; or UTC: Universal Time, mostly used by the observers). Before 1972 Jan. 1, UTC is replaced by UT1.
- the format in which the starting date
or the given series of dates are provided.
-
for some satellites, it is possible to get an estimate of the precision of the ephemerides:
check the button "get precision if available"and you will get such estimate
for each line of the ephemeris. Note that at the present time this information
is provided only for outer irregular satellites of giant planets as described in Emelyanov (2010)
- Only in the case of the tabulated ephemerides with a constant
step
- the date of the first calculation
- the unit of the step, the value of the step and the number of steps
- the data in output (cf below)
For topocentric coordinates, it is possible to select only
the dates where the object is visible (check the last item of the list).
- Only in the case of ephemerides for a series of dates
- the format of the observational data if so
(in that case click on "Enter your observations to calculate O-C")
- if no observations (only a series of dates) click
on "Enter a set of dates to generate ephemerides"
- insert the series of dates together with observations if so to get (O-C)s.
More details on this facility are given
here
- To start the calculations, click on "Calculate"
Data in output:
The list of all the possibilities is available here.
Note that if you enter a series of observations,
the format of the data must correspond to your data.
Reference
-
Emelyanov N.
Precision of the ephemerides of outer planetary satellites.
Planetary and Space Science. 2010. V. 58. P. 411-420.
Graphical representation of the satellite configurations
for each planetary system
A software allows to draw the configurations of the satellites
for each planetary system. The input page is similar to the page
for the classical ephemerides with a constant step
from an initial date but asks for the graphical specificities.
Specific parameters in input:
- the satellite which will be cross-marked
- the satellite (or planet center) which will be put
at the center of the field
- the type of coordinates that you wish for the positions displayed on the screen
- the initial scale for the field displayed on the screen (you may modify the scale later if necessary)
To start the calculations, click on "Show"
More details on this facility
here
Phenomena of the satellites
Several pages provide predictions of phenomena:
- Search of mutual phenomena and eclipses by the planet:
this page allows to calculate the events which will take place
at any period of time of your choice.
You must provide the following parameters:
- an interval of time from an initial date
- a duration for the calculation in order to avoid to wait too much time (note that it is anyway limited to 5 minutes).
- the type of phenomena that you are looking for
(mutual, eclipses by planet for main satellites and/or
inner satellites)
- Pre calculated phenomena for periods of time
where phenomena.
In that case a filter (selection of the observing site) allows
to obtain only the visible events from this site.
To start the calculations, click on "Calculate".
More details on this facility
here.
Special ephemerides
Maximum elongations:
Choose the type of maximum elongation :
- maximum elongations in the equator of the planet
- maximum elongations in the orbital plane of the satellites
- maximum and minimum distance
- maximum elongations in X tangential Earth equatorial coordinates.
The data in input are similar to those for the ephemerides of positions.
From an initial date, you will ask for a number of elongations
to be calculated.
To start the calculations, click on "Calculate".
More details on this facility are given
here
Ephemerides of inner and co-orbital satellites of Saturn
for infrared observations
These ephemerides allow to obtain favorable configurations
to observe inner co-orbital satellites of Saturn
(see explanatory pages ).
The data are the favorable dates for infrared observation.
More on the ephemerides of the natural planetary satellites
Features of the ephemerides for a given series of dates
and possible calculation of (O-C)s from observed positions.
This tool is used for two purposes.
• First, it is possible to enter, in tabular form,
a series of dates for which ephemerides will be calculated.
For the dates, you have the choice between the following formats:
Year, month, day, hour, minute, second
Year, month, day, fraction of day
Julian date
Modified Julian Date
• Second, it is possible to enter inside the window
a series of observations following the dates and
to obtain the residuals (O-C) for all these observations
from the ephemerides at once as well as some statistics (average,
rms and standard deviation).
The choice between these two possibilities is made
by the user by means of radio buttons on the web page.
Formats of input dates and observed values are selected
from the corresponding menus.
Then, on each line of the window, the date of observation
(or for ephemerides) is entered and, if necessary,
observational data in right ascension and declination
or in any other type of coordinates proposed as ephemerides output.
All the entered values are to be separated by one
or more blank spaces.
To enter data into the window it is convenient
to use the clipboard.
At last the user will click on the "Calculate" button.
A new page will appear displaying the (O-C) results
or the calculated ephemerides. The results may be copied
into user's files using the clipboard.
The units of (O-C) results are always arcseconds.
The table with the results is followed by the mean values of the (O-C),
the root-mean-square of the residuals (O-C) between observed
and calculated positions of the satellite and the standard deviation.
Note that this web tool also allows to compare ephemerides
by entering a set of calculated positions as observed positions.
You may enter your own calculations or compare the ephemerides
proposed here by entering the results of calculation
for an ephemeris as observed positions to be compared
with another ephemeris.
Features of the graphical representation of the satellites
systems
After clicking on the "Show" button a new page will appear
providing the graphical representation of the satellite
system configurations. The comments and menus are similar
to those on the parent page.
Choosing new values of the configuration parameters,
you may refresh the page to get the new configuration.
It is possible to run step by step in order
to see the evolution of the system.
To know which satellite is which one, pass the mouse
on the considered point.
To see the relative
coordinates and magnitudes of satellites you may click
on the
"Coordinates and magnitudes"
link on the page of the graphical
representation.
Features of the search for mutual occultations and eclipses
and for eclipses of the satellites by the planet.
After choosing this option,
you have to choose a system of satellites
and enter some parameters as explaned above to provide
the date of the beginning and the end of the period of events.
After clicking on the "Calculate" button,
the computation starts running up to the time limit expiration.
Mutual events
A table on the output page shows the parameters and satellites.
The type of the event is given under the form "nEm" or "nOm"
where n is the number of eclipsing or occulting satellite,
m is the number of eclipsed or occulted satellite.
The circumstances of each detected event are also given.
For a mutual occultation or eclipse they are the date of
the beginning and of the end of the event.
Then follow type, duration, impact factor,
combined magnitude of the satellites, maximum magnitude drop,
apparent distance of the involved satellite from the planet limb
and apparent distance between the of eclipsed or occulted one.
"E" denotes an eclipse and "O" denotes an occultation.
The impact factor is equal to zero if it is a central
passage of satellite through the shadow or through
the apparent disk of the other satellite. The impact factor
is equal to unit 1 in the case of a grazing event.
Negative value of the distance from the planet limb occurs
if the occulted or eclipsed satellite is on or under
the planetary disk.
Note that in the case of mutual eclipses, the start of the event
is assumed as the first contact of the eclipsed satellite
with the penumbra of the eclipsing one, and the end of the event
is assumed as the last contact.
After the table providing the ephemerides,
the last date tested for events is provided.
You may use this value to restart the search
if you wish to continue further.
Eclipses by the planet
In the case of the search for eclipses of the satellites by the planet,
the planet is denoted "0" and the time is shown in brackets
for the event starting or ending invisible from the Earth.
In this case the distance to the planet limb is omitted.
In the case of the eclipses by the planet, the penumbra
from the planet with the corresponding limiting cone
and complete shadow with the corresponding cone
are taken into account. The shape of the planet
is approximated by an ellipsoid with known equatorial
and polar radii. The beginning of the eclipse
is at first touch of the penumbra by the satellite.
The end of the eclipse is the last touch of the penumbra
by the satellite. The time of "last speck"
when the trailing limb of the satellite enters the shadow cone,
and the time of "first speck" are provided in the output data
(two last columns).
Note that the brightness of the satellite
is changing only between the beginning of the eclipse
and "last speck" and between "first speck"
and the end of the eclipse.
Features of the search for the times of maximum elongations
of the satellites.
After choosing this option, you have to choose a system of satellites
and some parameters as explaned above for the search of events.
Choosing the times of maximum elongations of satellites,
the table on the output page presents the times followed
by the coordinates of the satellite measured
in the apparent planet centered coordinate system
that you choose for the elongations.
The Y-axis (denoted B) is towards the pole
of the planet if you choose "planet-axis",
of the orbit if you choose "orbit-axis"
and of the Earth pole if you choose "in X".
If you choose elongations in distance,
the positions provided will be distance
and position-angle in Earth-equatorial system.
The X-axis (denoted A) is at 90 degrees
in counterclockwise direction. The position
angle of the B axis is also given under
the denomination Tilt.
Intervals of time where ephemerides are calculated.
The dynamical models used for our ephemerides allow
to get a good accuracy on an interval of time of several decades.
However, the calculation of the ephemerides
is done upon a larger interval of time.
If using an analytical model, it is theoretically possible
to make the calculation at any time either in the past
or in the future. However, this calculation
has no sense as soon as the error on the position
of a satellite in its orbit reaches 180 degrees.
For a numerical model, the limit is given
by the model itself which is calculated for
a given interval of time.
The calculation of the ephemerides is made,
in general, when possible, to any date inside
the interval 01/01/01 - 27/08/3026.
We have to notice that if you wish to calculate
absolute coordinates of a satellite (right ascension
and declination) it is necessary to have the planetary
ephemerides which will be involved directly
in the satellite coordinates.
We propose to choose between a set of planetary
ephemerides
(INPOP17a, INPOP13C, INPOP10, EPM2017,
DE431, DE421, DE405, DE406, DE200, VSOP87)
which are available on time intervals
smaller than the interval proposed above
(see the page "Sources of the data").
Ephemerides of the outer (irregular) satellites
are calculated using original numerical models built
for given time intervals depending on the sample
of observations available to fit the ephemerides.
Be careful, for different satellites,
the intervals of validity of the numerical models are different.
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Dates of the first and the last observations
used for the ephemerides and intervals of validity
of the numerical ephemerides of the satellites of :
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Jupiter
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Saturne
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Uranus
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Neptune
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