Question about ASTRO

Author	Message
matherp Guru Joined: 11/12/2012 Location: United Kingdom Posts: 11435	Posted: 06:43pm 07 May 2026       Here is the explanation. Obviously you are correct if no flip is needed but the move is complex if it is. The new function covers both. My scope will be completely computer controlled so if I ask it to point to a new object it needs to know the full process for that. Likewise, even tracking a flip is needed if the meridian is crossed.   Quote   A telescope flip (usually called a meridian flip) is a manoeuvre that a German Equatorial Mount (GEM) must perform when a target crosses the local meridian. It’s a geometric necessity of the mount design, not a software quirk. ⭐ The core idea A GEM cannot track an object indefinitely on one side of the sky because the telescope tube will eventually collide with the mount or tripod. So when the target crosses the meridian (the north–zenith–south line), the mount must: Move the telescope to the opposite side of the RA axis while keeping it pointed at the same coordinates. That is the flip. 🧭 Why the flip is required A GEM tracks by rotating the Right Ascension (RA) axis. But: The RA axis has limited rotation before something hits something else The counterweight bar must always point down for stability Cables, camera, and focuser all have physical limits If the mount kept tracking past the meridian without flipping, you’d get: OTA hitting the tripod Counterweights rising above the telescope Cable strain or motor housing collision So the flip is a mechanical safety requirement. 🔧 What physically happens during a flip A meridian flip is a two‑axis manoeuvre: 1. RA rotates by exactly 180° (12 hours) This moves the telescope from the east side of the mount to the west side (or vice‑versa). 2. DEC rotates to re‑acquire the same declination Because flipping RA alone points the telescope to the mirror position, the DEC axis must rotate to bring the telescope back onto the original target. After these two motions, the telescope is pointing at the same RA/DEC, but the tube is on the opposite side of the mount. 🕒 When the flip happens A flip is triggered when: The target’s Hour Angle becomes slightly positive (i.e., it has crossed the meridian) Or the mount hits a user‑defined limit (e.g., “track 5° past meridian”) Edited 2026-05-08 04:54 by matherp