The main Ephemeris Interpolator window is displayed when the application first starts and is where ephemerides can be added or removed and where all other windows (e.g. the Pad or Settings) are accessed from.

Click on parts of the window to jump to more information:

ToolstripTabsDrop-down listDrop-down listMPES / Scout settingsNEOCP filtersNEOCP filters and settingsEphemeris lines areaDate and TimeMessage areaMessage areaRARARACopy RA and DecCopy RA and DecDisplay position in Google SkyDisplay position in Google SkyDecSpeed and PA°Set time to nowTime2CalculateCalculateUndock and dock PadUndock and dock PadPad3Ephemeris fitPacked IDMatched ephemeris formatMPES / NEOCP visible only?Previously calculated timesMPES / NEOCP visible only?Previously calculated timesMPES / Scout settingsNEOCP settings


See the Toolstrip topic for detailed information


Each time an ephemeris is added a tab is also added to the tabs area, displaying the object name and [qualifier] if entered.

Select a tab by clicking on it. The currently selected tab is indicated with a yellow square and its associated ephemeris is displayed in the Ephemeris Lines area. The Home, End, Left arrow and Right arrow keys can be used to move the selection within the list of tabs.

Press the Delete key to remove the currently selected tab, or Ctrl+Delete to be prompted to remove all tabs.

Drop-down list

Click on the drop-down arrow to display a summary of all the objects currently stored in tabs. Select an object by clicking on a line in the list, the appropriate tab will be selected.

The approximate RA, Dec and speed is displayed in the drop-down list and for objects added from the NEOCP also includes summary magnitude, absolute magnitude H, number of observations, observed arc (days) and number of days since last seen:

MPES / Scout / Horizons /NEOFixer settings

These settings control the downloading of ephemerides using the Retrieve MPES ephemeris, Retrieve Scout ephemeris and Retrieve Horizons ephemeris and Retrieve NEOFixer ephemeris online services.

Dates: Enter the number of ephemeris dates (lines) to be generated (see Notes). To achieve accurate interpolation, the number of dates actually requested may be increased automatically, see Determining the interpolation method.

Interval and Unit: Enter the step size for the ephemeris. Unit can be Days, Hours or Minutes.


  • For MPES, Horizons and NEOFixer ephemerides, the ephemeris lines may be reduced if the "MPES/NEOCP visible only?" checkbox is ticked. Scout and Horizons ephemerides are unaffected.
  • Ephemerides returned from NEOFixer always have a step size of 15 minutes. The requested number of dates, interval and unit will be used to determine the equivalent needed for a 15 minute step size.

NEOCP filters and settings

These filters and settings control the downloading of ephemerides using the Retrieve NEOCP ephemeris online service.


When the Retrieve NEOCP ephemeris button is pressed, filters are only applied if Object is left blank. If it is left blank then all current NEOCP objects will be tested against the filters described below and only objects that satisfy the filter conditions will be added or updated in the set of tabs. The filters are only applied when ephemerides are downloaded and added to the list of tabs.

Class: 1, 2, 3. See Class for more information.

Only objects with a class that match any of the classes ticked in this filter will be selected. 

PCCP: Selects objects that are currently listed on the Possible Comet Confirmation Page. This filter takes precedence over filtering performed using Class, i.e. even if the class of an object on the PCCP is not ticked, it will still be selected if the PCCP filter is ticked (and the remaining filters of Score and Faint limit are also satisfied).

Score >=: Only include NEOCP or PCCP objects with scores greater than or equal to the value entered. If 0 is entered then all objects will pass this filter. Score is one of the information columns given on the NEOCP and PCCP.

Faint limit: Only include NEOCP or PCCP objects equal to or brighter than the magnitude entered. Note: The faint limit is applied to the ephemeris magnitude for the ephemeris date immediately before the required date and time. For rapidly brightening or fading objects this may affect filtering, depending on the required date and time entered.


Units defines the ephemeris step size that will be generated by the MPC's NEOCP service. The number of ephemeris lines generated depends on the chosen ephemeris interval:

  • 1 hour interval generates 25 lines, spanning 24 hours
  • 30 minute interval generates 49 lines, spanning 24 hours
  • 10 minute interval generates 60 lines, spanning 10 hours
  • 1 minute interval generates 121 lines, spanning 2 hours

NEOCP ephemerides always start on an integral hour. The start date and time of the generated ephemeris will be adjusted if necessary to ensure there is adequate coverage on either side of the requested date and time to allow good interpolation.

For an object that is accelerating or decelerating quickly (probably a fast moving object), check the interpolation fit to see whether the ephemeris interval should be reduced to achieve better accuracy in the interpolated positions.

MPES/NEOCP/NEOFixer visible only?

When ticked, only ephemeris lines where the object is above the horizon and the Sun is below the horizon are included. Only applied when ephemerides are downloaded from the MPES, NEOCP or NEOFixer services.

Ephemeris Lines

An editable text area where ephemerides are stored for the selected tab. When ephemerides are downloaded using one of the online services ( Retrieve MPES ephemeris, Retrieve NEOCP ephemeris, Retrieve Scout ephemeris, Retrieve Horizons ephemeris and Retrieve NEOFixer ephemeris) or are imported from Find_Orb using the Add last ephemeris generated in Find_Orb button, the text is automatically added. For other ephemerides, see Add an ephemeris manually.

Date, time

Enter the required date and time to calculate position and motion details for. This date and time is used to determine a suitable start time when downloading ephemerides from the MPES, NEOCP and Scout online services to ensure there are enough ephemeris lines before and after the requested times.

Date is entered in two separate fields, with year and month in the first (in yyyy mm format) and day of the month in the second. A decimal day (e.g. 10.806944) can be entered (or pasted) in to the Day field and will cause the equivalent day, hour, minute and second to be extracted and used to fill the appropriate time fields.

Time is entered as three separate fields, in hh, mm and ss format. Although rarely justified, seconds can include decimals.

Note: The time can be adjusted (incrementing and decrementing by hours, minutes or seconds) using the Adjust Time buttons on the Pad and this automatically adjusts the date if needed.

RA and Dec

The RA, Dec values are updated when the Calculate button is pressed. The currently displayed RA and Dec can be copied to the clipboard with the Copy RA and Dec button.

Calculate time when RA reaches ... context menu option

Calculate time when Dec reaches ... context menu option

The RA field can be manually over-typed and then right-clicked with the mouse to display the 'Calculate time when RA reaches ...' context menu option. Use this option to update the Date and time to show when the manually entered RA value is reached. This can be useful to judge when a moving object may reach the proximity of a star, or edge of field etc. The Dec field can also be used in the same way.

Note that the manually entered RA or Dec values should be within the range of ephemeris RA and Dec values for an accurate date and time to be calculated.

Copy RA and Dec

Copies the currently displayed RA and Dec to the clipboard.

The Copy RA and Dec buttons shown on the Ephemeris Interpolator and Pad provide the same functionality.

Display Position in Google Sky

When this button is pressed, RA, Dec, Speed and P.A.° are recalculated using the currently entered date and time. The date and time and the calculated values are then combined with the current GoogleSky KML template before starting GoogleEarth. See Display a position in Google Sky step by step for detailed information.

Note: The Display Position in Google Sky button is only enabled if the GoogleSkyFieldSize setting is greater than 0 and the (free) GoogleEarth application is also be installed. See GoogleSky integration and also the Google Earth Pro on Desktop section on the page.

The Display position in Google Sky buttons on the Ephemeris Interpolator and Pad provide the same functionality.

Speed, P.A.°

The calculated speed of motion (arc-seconds per minute) and Position angle of the direction of motion (P.A.°) for the entered date and time. Clicking the mouse into either field copies its value to the clipboard (the field background turns  green  momentarily to show the copy has been done). 

Set time to now

Update the date and time fields with the current time (in UTC). Seconds are set to zero.


Uses the currently entered date and time to calculate values for RA, Dec, Speed and P.A.° using a third order interpolation method.

If the entered date and time is not between the first and last ephemeris dates then the calculation cannot proceed and the calculated quantities will be shaded  red .

If the ephemeris values are accelerating or decelerating rapidly (e.g. during the close approach of a NEO) then the interpolation fit may highlight in red if the ephemeris interval (step size) is too large. Consider reducing the ephemeris interval to achieve more accurate calculated results. Note that for downloaded ephemerides there are separate controls for NEOCP/PCCP ephemeris intervals and units and MPES, Scout, Horizons and NEOFixer ephemeris intervals and units.

The Calculate buttons on the Ephemeris Interpolator and Pad provide the same functionality.

Previously calculated times

Each time Calculate is pressed with a new date and time for an object, that date and time are added to this drop-down list. They can be selected later to re-establish the same date and time as used previously if e.g. re-stacking the same set of images again after having changed the date and time or the object for processing a different stack. The most recently used date and time is at the top of the list. The list of times is stored independently for each stored object.

The times can be cleared if required by right-clicking in the list and selecting the option to clear the previous calculator times for the currently selected object.

The 'Previous calculated times for current object' drop-down lists on the Ephemeris Interpolator and Pad provide the same functionality.

Undock pad and Undock pad and minimise

Undock pad causes the Pad window to be displayed, leaving the Ephemeris Interpolator window also visible.

Undock pad and minimise causes the Pad to be displayed but minimises the Ephemeris Interpolator window to free up screen space.

See also the complementary Dock and Dock and minimise controls on the Pad.

Note that the Pad attempts to keep itself 'on-top' of other windows when not minimised and therefore always visible but this is sometimes affected by the behaviour of other applications (including Astrometrica) and can result in it being occasionally covered by another application's window. If this occurs you may need to click on the Ephemeris Interpolator in the task bar to make it visible again.

Information (Status) bar

Various areas showing the operational state of the application are displayed, as described below:

Message area

Informational, warning and error messages area. The message is also displayed as a tool tip if the mouse is moved over the message area.


Indicates the current interpolation order of fit for the requested date and time and for the range of ephemeris dates available. The fit can be 3rd order, 2nd order or Linear.

An estimate of the error due to the interpolation calculation is also given and will be highlighted in red when the error exceeds 1 arc minute. The true error is likely to be somewhat larger than the estimate indicates. To reduce the error, re-obtain the ephemeris with a reduced ephemeris interval and ensure there are at least two ephemeris lines before and after any date and time to be calculated. As linear interpolation does not allow any estimation of errors, the Fit area displays "Linear" highlighted in red.

See Interpolation for more information.

Packed ID

If the object is permanently numbered or has a provisional designation issued by the MPC then the equivalent packed designation is displayed, otherwise is left blank. To copy the packed name to the clipboard, hold the Ctrl key and click on the Copy object name button, or hold the Ctrl key and right-click on Object.

Matched format

When an ephemeris is added it is matched to a known ephemeris format (see the Ephemeris Formats Editor) and the matched format name is displayed here. The remarks from the stored ephemeris format are displayed as a tool tip if the mouse is moved over the Matched format area. Some remarks contain a list of column headings and to temporarily transfer the remarks to the message area, click on the Matched format name. See Using the Editor for information on editing ephemeris format remarks.

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