Calculate Julian Date
The Calculate Julian Date command calculates the geocentric or heliocentric Julian Date for an image and save the result in the image header. Note that the image must be saved to a file to make the addition permanent. Both the standard and modified forms are available as JD and MJD for regular geocentric Julian Date, or HJD and MHJD keyword for the Heliocentric Julian Date. The Julian Date can also be calculated and parsed using a simple script (see the sample script, "Julian Date Function Test.lua").
The Calculate Julian Date command opens
from the Image Window's Process >
Utilities menu and the Utilities
submenu of the 
button on the
Main Toolbar. The "immediate" form,
shown first, opens when an image or image set is displayed in the
top-most window. The general form can be used to select source
images from folders, windows, or by matching templates.
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Calculate Julian Date Properties |
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Profile [|>] |
Selects the parameter profile for this command and allows you to save or work with existing presets. |
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[Select] |
Opens the Select Source Images dialog to choose images from an image window, folder, files, name template, or a Mira File List. |
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Julian Date Type |
Selects the Julian Date type. This also selects the keyword used to save the result to the image header. JD selects the ordinary Julian Date MJD selects the Modified Julian Date which subtracts 2,400,000.5 from the JD and begins at midnight. HJD selects the Heliocentric Julian Date which adjusts the Julian Date to the Sun by removing the light travel time to Earth. This correction varies with direction in the sky. MJD selects the Modified Heliocentric Julian Date, which subtracts 2,400,000.5 from the HJD and begins at midnight. |
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JD Time Reference |
This adjusts the Julian Date value to account for exposure time. Beginning selects the beginning of the exposure. Middle selects the midpoint of the exposure time. End selects the end of the exposure. |
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Supporting Keywords |
These header keywords are used for the Julian Date calculation. Right Ascension and Declination are required only for calculating the Heliocentric Julian Date. |
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Right Ascension |
The right ascension coordinate in units of either decimal degrees or HMS. You must select the coordinate format from the adjacent list box. Decimal degrees is the standard FITS representation for angles. The FITS standard is for right ascension to be held in the CRVAL1 keyword and specified in decimal degrees. A common non-conforming usage is with the RA keyword and specified in HMS units, as hh:mm:ss.sss. |
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Declination |
The declination coordinate in units of either decimal degrees or DMS. You must select the coordinate format from the adjacent list box. The FITS standard is for declination to be held in the CRVAL1 keyword and specified in decimal degrees. A common non-conforming usage is with the RA keyword and specified in HMS units, as dd:mm:ss.sss. |
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UT Date |
The UT date of observation. The FITS standard is for date and time to be combined in the DATE-OBS keyword with the format yyyy-mm-ddThh:mm:ss.sss. |
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UT Time |
The FITS standard is for date and time to be combined in the DATE-OBS keyword with the format "yyyy-mm-ddThh:mm:ss.sss". FITS images saved before Jan 1, 2000 ("Y2K") use the obsolete keyword TIME-OBS with the format hh:mm:ss.sss. |
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Exposure Time |
The exposure time in units of seconds. The FITS standard is for exposure time to be held in the EXPTIME keyword. |
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Check this box to confirm the calculations in a Text Window. |
Mira Pro x64 User's Guide, Copyright Ⓒ 2023 Mirametrics, Inc. All
Rights Reserved.
Verbose Output