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).
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
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.
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.
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
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.