How to read A/B codes
Quick start (3 steps)
- Choose coordinate input unit (hms/dms or deg).
- Enter point A and point B (Right Ascension and Declination (RA/Dec)).
- Compute separation and Position Angle (PA) (north=0°, eastward positive).
Inputs
Results
| Separation (deg) | — |
|---|---|
| Separation (arcmin) | — |
| Separation (arcsec) | — |
| Position angle PA (deg) | — |
This tool runs in your browser. Inputs are not sent.
Interpretation & notes
- Separation is the great-circle distance on the celestial sphere.
- PA is measured from celestial north (0°) toward east (90°).
- PA is normalized to the range 0..360°.
How to use angular separation effectively
Enter both sky positions in the same unit system, then compute once before changing anything. Keep the first pair as your baseline so it is clear which coordinate change altered the separation or position angle.
What to check first
Confirm whether you are entering sexagesimal values or decimal degrees. A mismatch between those two formats is the most common reason for an unexpected result.
How to read the output
Use the degree, arcminute, and arcsecond values as different views of the same separation. The position angle is measured from celestial north toward the east, normalized to 0-360°.
Common mistakes to avoid
- Mixing hms/dms input with decimal-degree values in the same run.
- Swapping point A and point B without noticing that the position angle can change.
- Comparing rounded arcsecond values without checking the degree result underneath.
- Sharing a result without copying the URL that stores the exact coordinates.
See also
FAQ
How is separation measured on the celestial sphere?
Separation is spherical distance on the sky, so it respects celestial coordinates and curvature.
Why is PA normalized to 0-360 degrees?
PA is an orientation. Wrapping to 0-360 keeps a single unambiguous output format.
What should I do first on this page?
Start with the minimum required inputs or the first action shown near the primary button. Keep optional settings at defaults for a baseline run, then change one setting at a time so you can explain what caused each output change.
Why does this page differ from another tool?
Different pages often use different defaults, units, rounding rules, or assumptions. Align those settings before comparing outputs. If differences remain, compare each intermediate step rather than only the final number.
How reliable are the displayed values?
Values are computed in the browser and rounded for display. They are good for planning and educational checks, but for regulated or high-stakes decisions you should validate assumptions with official guidance or professional review.