Linked astronomy tools
Use these pages when the alignment setup needs time, visibility, or imaging checks before field work.
Quick start (3 steps)
- Enter location, date/time, and timezone.
- Choose hemisphere, reticle preset, and optional mirror/rotation/offset calibration.
- Use the reticle angle, clock direction, and time-series to align and re-check quickly.
Inputs
Results
Reticle
Time series
| Local time | Angle (deg) | Clock |
|---|
Definitions & notes
- Drawing angle: 0°=top (12 o'clock), 90°=right, 180°=bottom, 270°=left.
- Clock direction is clockwise from 12 o'clock.
- HA is computed as (LST - RAstar) mod 24h.
- Apply order is fixed: offset → mirror_x → display_rotation_deg.
- Time-series chart uses unwrapped angle to avoid wrap spikes.
How to use the polar alignment workflow effectively
Use this page to translate a location, time, hemisphere, and reticle setup into a pole-star position you can repeat at the mount.
How it works
The calculator resolves the observation time, computes local sidereal time, selects Polaris or Sigma Octantis, then converts the hour angle into reticle angle and clock position. Mirror, rotation, and offset settings are applied after the astronomical angle so the preview matches your finder orientation.
When to use
Use it before a session to confirm the target clock position, during setup to check a calibrated reticle, and after a wait to see how quickly the position drifts. The time-series table is useful when you expect to align more than once during the night.
Common mistakes to avoid
- Using the computer time zone when the mount is set to a different local time or UTC offset.
- Forgetting that a mirrored or rotated reticle changes the displayed placement even when the sky angle is unchanged.
- Leaving hemisphere or pole-star selection on auto when the latitude is near zero or the site is entered incorrectly.
- Treating the reticle preview as a mechanical collimation check; verify the mount and polar scope separately.
Field check
Run the current time, align to the displayed clock position, then re-run a later time from the series if the setup takes longer than planned. If the clock direction jumps unexpectedly, review longitude sign, time zone, and display transform first.
See also
FAQ
What inputs matter most for the reticle angle?
Latitude, longitude, date and time, time zone, hemisphere, pole-star choice, reticle preset, and any mirror/rotation/offset calibration all affect the displayed placement.
Why does mirror or 180° rotation change the target position?
The sky angle is computed first, then display transforms are applied to match the view through your reticle or polar scope. Use the same transform you see at the mount.
How should I use the time-series output?
Check the current clock position before alignment, then compare later rows if setup takes time or if you need to re-check during a long imaging session.
Is this a replacement for mechanical calibration?
No. It gives a repeatable placement target, but polar scope centering, reticle calibration, mount leveling, and final drift checks still depend on your equipment.
Is my input uploaded somewhere?
Core calculations run locally in your browser. Some pages encode parameters in a shareable URL, but no automatic upload is performed unless you explicitly share that link.