AstroCC Coordinate Converter Help

Authors: Karen Collins and John Kielkopf of the University of Louisville. AstroCC is open source software and is distributed under the terms of the GNU General Public License. Report problems to karen_dot_collins_at_insightbb_dot_com. Parts of AstroCC are based on XmTel, WCSTools, Nuvola icons, and ImageJ open source software packages. Solar system object coordinate calculations and internal HJD/BJD calculations are based on code adapted from JSkyCalc which was written by John Thorstensen of Dartmouth College. BJD values may also be retrieved from http://astroutils.astronomy.ohio-state.edu/time/utc2bjd.html which is based on Eastman et al. 2010. Coordinate data are obtained from SIMBAD. Leap second data is obtained from the U.S. Naval Observatory at http://maia.usno.navy.mil/ser7/tai-utc.dat. The observatory data were compiled from the ESO website at http://www.eso.org/~ndelmott/obs_sites.html which credits the U.S. Naval Observatory and the H.M. Nautical Almanac Office. The lunar phase images are adapted from Lunar_libration_with_phase_Oct_2007.gif from Wikimedia Commons (submitted by Tom Ruen).

Features

AstroCC is a coordinate and time conversion utility for astronomy. It accepts an object designation or the coordinates of an object and calculates coordinates in alternative systems, and at different dates, times, and locations. It also provides lunar and bright planet coordinates to aid in planning observations.

-          Accesses SIMBAD to lookup coordinates by object name

-          Converts astronomical coordinates to/from common coordinate systems

-          Converts time to/from UTC, local, JD, LST, HJD, BJD

-          Provides twilight time for epoch of interest

-          One-click access to full SIMBAD data

-          One-click access to Sky-Map field

-          Provides ephemerides for the Moon and major planets

-          Supports leap second data with one-click internet update

-          Displays moon phase at epoch of interest

-          Displays proximity and altitude of Moon and major planets

-          Extensive (customizable) selection of observatory locations

Overview of operation

The AstroCC coordinate converter user interface is shown below. The top row shows the current date and time in UT, local time, Julian Date, and local sidereal time (LST) formats. These and other items with a gray background cannot be modified by the user. Tooltips are provided for each item to describe its use and syntax. Tooltips can be disabled under the Preferences menu.

The desired Observatory ID should be selected (in the second row of fields), and the Longitude, Latitude, and Altitude fields will be updated automatically. Otherwise select “Custom Lon, Lat, Alt entry” as the observatory ID (the first item in the list) and enter the Longitude, Latitude, and Altitude entries directly. If any other Observatory ID entry is selected, the Longitude, Latitude, and Altitude fields will be disabled.

If a time zone different from your computer’s current time zone setting is desired, deselect the Preferences menu item “Use computer time zone…” and manually enter the UTC offset in hours.

Enter a valid SIMBAD Object ID and press <Enter>. If the object ID and relevant data are found in SIMBAD, the Target Proper Motion Right Ascension (RA) and Declination (Dec) fields and the Standard Coordinates J2000 Equatorial RA and Dec fields will be updated automatically. A green border will be placed around those coordinate fields indicating that they are the active fields from which all other coordinates are calculated. Also, major solar system object names may be entered (Moon, Mercury, Venus, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto) or the associated proximity box at the bottom of the user interface can be clicked to automatically enter the object name. When a solar system body is entered, the Epoch of Interest Equatorial RA and Dec fields will be updated automatically since these objects do not have a (relatively) fixed RA and Dec. While a solar system object name is entered in the Object ID field, the active coordinate fields cannot be changed. To do so, remove the solar system object name from the Object ID field.

Instead of entering a SIMBAD Object ID, coordinates can be entered directly into an appropriate pair of coordinate boxes. Press <Enter> after typing or pasting the coordinates. Entering a coordinate directly will clear the SIMBAD Object ID text and proper motion values. Proper motion values will not be cleared if the SIMBAD Object ID box is empty. Any coordinate pair can be used as the source to calculate all others (except for the case of major solar system bodies). The border for the entered coordinates will become green to remind the user which coordinates are being used as the source for the computation of the other coordinates. For convenience, both coordinates of a pair can be typed (or cut/pasted) into one of the boxes of a pair. When <Enter> is pressed, the coordinates will be separated and placed into the appropriate boxes (see “Numbers, Bases, Formats, and Indicators” section below for syntax details). While a solar system object name is entered in the SIMBAD Object ID field, the active coordinate fields cannot be changed. To do so, remove the solar system object name from the SIMBAD Object ID field. 

Finally, the Epoch of Interest should be entered. Click the Now button to set the epoch of interest to your computer’s current time. Select Lock to keep the epoch of interest locked to your computer’s time every second. Otherwise, the epoch of interest can be entered as UT date and time, local date and time, Julian Day, Heliocentric Julian Day (HJD) or Barycentric Julian Day (BJD). All other date formats will be calculated from the entered format. The mouse scroll wheel can be placed over a UTC or Local date/time component value to increment/decrement that specific value (i.e. roll the wheel over year, month, day, hour, minute, or second to change the specific component’s value). Alternatively, the up/down arrows to the right of UTC and local time can be clicked to increment/decrement the date/time by one step. The time step can be set by right-clicking the up/down arrows or the JD time field. The mouse wheel will also increment/decrement time if the mouse pointer is located within the JD field. Evening and morning nautical twilight start/end times are also shown for the epoch of interest. Click inside these fields or on the adjacent icons to set the current time to the corresponding twilight time. If the epoch of interest falls between evening and morning twilight, the twilight field backgrounds are set to green.

For accurate dynamical time and coordinate calculations, leap second data must be kept current. To do so, simply press the Update button while connected to the internet and the data will be downloaded into AstroCC and stored along with other program preferences. New leap seconds may be introduced every six months at the end of the day on June 30 and December 31. New leap second announcements are made several months in advance. Simply click the Update button once every 3-6 months to check for an update. If Auto is selected, an appropriate leap second value is determined for the epoch of interest (this option does NOT automatically update the leap second table). A green Leap-secs background indicates that the displayed number of leap seconds is from the leap second table. The table is valid from 1/1/1961 though the current epoch. Outside this range, leap seconds must be estimated. To estimate leap seconds, AstroCC uses the formulae of Espenak and Meeus 2006, which cover the range from 1999 BCE to 3000 CE. If the epoch of interest is within this range, the Leap-secs background color is yellow, otherwise the background color is red indicating a leap second value has not been calculated. If Auto is not selected, the field background is white, and the user can enter a custom number of leap seconds.

The Phase-Altitude-Proximity section under Epoch of Interest shows the illuminated portion of the moon at the epoch of interest and the altitude of each solar system object (top number) and the distance from the current object coordinates (bottom number). A green background indicates that observations of the target of interest at the epoch of interest should be minimally affected by the solar system object. Yellow means the objects are near each other, and red means the objects are very near each other. A mouse click on the data field of a particular solar system body will make that object the current object of interest and its full coordinate conversions will be shown in AstroCC.

The SIMBAD button in the Standard Coordinates section will open a link to SIMBAD using your default browser. If the SIMBAD Object ID field contains text, a SIMBAD object query using that text will be issued. If the SIMBAD Object ID field is empty, a SIMBAD coordinate query will be issued using the RA and Dec coordinates in the J2000 Equatorial fields.

The Sky-Map button in the Standard Coordinates section will open Sky-Map.org using your default browser and request a display of the sky centered on the coordinates in the J2000 Equatorial fields.

Numbers, Bases, Formats, and Indicators

Fields with a gray, green, yellow, or red background cannot be directly modified by the user. Fields with a white background can be directly modified by the user. The coordinate pair with green borders indicates the active coordinate pair. All other coordinates are calculated using the active coordinates as the source. Coordinate conversion formulae are not exact, so pressing <Enter> in a new coordinate pair (using the existing values) may result in a slight change to the other computed coordinate pairs.

RA, UT, and local time must be entered in hours. All other coordinate numbers must be entered in degrees. Observatory latitude is in degrees (north positive) and observatory longitude is in degrees (east positive). Proper motion is in SIMBAD milli-arcsec per year (mas/yr) format. UT and local date is in YYYY MM DD.DD format. Hour Angle (HA) is reported in the range -12:00:00 to 00:00:00 indicating sidereal hours until the object crosses the meridian and 00:00:00 to 12:00:00 indicating sidereal hours since the meridian crossing.

All numbers except UT and local date can be entered in decimal format (i.e. dd.d) or in sexagesimal format (i.e. dd.d mm.m ss.s). To facilitate cut and paste of coordinates from other sources, coordinate parsing is lenient and treats any contiguous set of nonnumeric characters as a delimiter. If more than one delimited set of numbers is found in a coordinate field, sexagesimal format is  assumed. For convenience, both coordinates of a pair can be typed (or cut/pasted) into one of the boxes of a pair. When <Enter> is pressed, the first coordinate set of 3 delimited numbers will be automatically placed in the left-most box of the pair and the second coordinate set will be placed in the right-most box. If a plus or minus sign precedes any delimited number in the set other than the first number, that component will be taken as the starting point of the second coordinate.

Preferences

Several options are provided under the Preferences pull-down menu at the top of the user window. After closing the program for the first time, a new file named “AstroCC_Prefs.txt” will be created (or in the AstroImageJ Coordinate Converter version, the preferences are saved along with the AstroImageJ preferences). On Microsoft Windows computers, the file is saved in the same directory as the AstroCC.jar file (AstroCC should be installed in a directory with user write access). On Linux systems, the preferences file is saved at home/.astrocc/AstroCC_Prefs.txt. On Apple OS X systems, the file is saved at home/Library/Preferences/AstroCC_Prefs.txt. This file will automatically load at startup and allows preferences, leap seconds, and other settings to be maintained across sessions.

Show coordinates in sexagesimal format
deselected – all coordinates are displayed in decimal format (i.e.  dd.dddd or hh.hhhh)
selected - all coordinates are displayed in sexagesimal format (i.e. dd:mm:ss.ss or hh:mm:ss.ss)

Use Harvard SIMBAD Server, deselect to use CDS Server
deselected – use the SIMBAD server at the
Centre de données astronomiques de Strasbourg (CDS), France
selected – use the SIMBAD server at Harvard

Use Ohio State BJD Server, deselect to calculate internally
deselected – calculate BJD internally (slightly less accurate [250 ms precision], but is fast and requires no internet connectivity)
selected – use the Ohio State server to calculate BJD (more accurate [20 ms precision], but slower and requires internet connectivity)

Use computer time zone, deselect to manually enter offset from UTC
deselected – enter offset from UTC in the Time Zone field
selected – use the time zone of the host computer’s internal clock

Use 12-hour local clock format, deselect to use 24 hour format
deselected – display Local time in 24-hour format
selected – display Local time in 12-hour (AM/PM) format

Show local twilight time, deselect for UTC format
deselected – display twilight time in Local format
selected – display twilight time in UTC format

Report SSBs as 'DOWN', deselect to show negative altitude
deselected – display negative altitudes in the Phase-Altitude-Proximity section when a solar system body is below the horizon
selected – display ‘DOWN’ in the Phase-Altitude-Proximity section when a solar system body is below the horizon

Show tooltips (field specific help displayed after hovering mouse over a field)
deselected – deactivates tooltip field specific help
selected – enables display of tooltips field specific help
NOTE: after a tool tip is displayed, move the mouse slowly around in a field to keep its tool tip displayed longer

Use custom observatory list (restart of AstroCC required)
deselected – use the internal list of observatories
selected – use an external list of observatories (observatories.txt – see ‘Customizing Observatory Data’ section below)
NOTE: AstroCC must be closed and restarted for this setting to take effect

Include proper motion correction
deselected – do not include proper motion correction to Epoch of Interest coordinates
selected – include proper motion correction to Epoch of Interest coordinates

Include precession correction
deselected – do not include precession correction to Epoch of Interest coordinates
selected – include proper motion correction to Epoch of Interest coordinates

Include nutation correction
deselected – do not include nutation correction to Epoch of Interest coordinates
selected – include nutation correction to Epoch of Interest coordinates

Include stellar aberration correction
deselected – do not include nutation correction to Epoch of Interest coordinates
selected – include nutation correction to Epoch of Interest coordinates

Include atmospheric refraction correction to altitude
deselected – do not include atmospheric refraction correction to Epoch of Interest altitude coordinate
selected – include atmospheric refraction correction to Epoch of Interest altitude coordinate

Customizing Observatory Data

An extensive list of observatories is stored within the program. If the user requires additional observatory selections, enable ‘Use custom observatory list’ in the Preferences menu. Then close and restart AstroCC Coordinate Converter. When the program is started, a file named observatories.txt is created and will contain the internal observatory data. This simple <tab> delimited file can be customized using any text editor. NOTE: to prevent previously customized data from being lost, if a file named observatories.txt already exists, it will NOT be overwritten. Therefore, if the user has an updated version of AstroCC and desires to customize the new internal observatory data, the existing observatories.txt file will need to be renamed or deleted.

The location of the observatories.txt file depends on the user’s operating system.

Microsoft Windows
AstroCC - in the directory where the AstroCC.jar file is installed
AstroImageJ Coordinate Converter - in the directory where AstroImageJ is installed

Linux
AstroCC - in the user’s home/.astrocc directory (NOTE: this is a ‘hidden’ folder)
AstroImageJ Coordinate Converter - in the user’s home/.imagej directory (NOTE: this is a ‘hidden’ folder)

Apple OS X
AstroCC and AstroImageJ Coordinate Converter - in the user’s home/Library/Preferences folder

 

The file is structured as a simple tab-delimited format. Using a text editor, new entries should be added using the following format:

Observatory Name<tab>ObservatoryLatitude<tab>ObservatoryLongitude<tab>Altitude

All numeric entries should be entered as decimal numbers (not sexagesimal).
Latitude is in degrees (positive north).
Longitude is in degrees (positive east).
Altitude is in meters above mean sea level.