Telescope mount
Polar alignment (where Polaris or σ Octantis sits on your polar-scope reticle right now, and drift alignment), setting circles (RA/Dec to altitude and azimuth and back, hour angle, sidereal time), and a GoTo controller over Web Serial for Celestron NexStar, Sky-Watcher SynScan and Meade LX200 mounts — connect, read where it points, slew, sync, nudge and stop. It refuses to slew near the Sun.
Added
Works with
- Observing planner Astronomysends a target here to slew to
How to use it
| Never point a telescope at the Sun without a proper solar filter over the front of it. Sunlight through a telescope or its finder blinds instantly and permanently, and can start a fire. The GoTo controller here refuses to slew within 20° of the Sun (you can raise that, never lower it below 10°), stops a slew or nudge that brings the telescope inside the limit while the Sun is up, and once inside lets you nudge only away. But it cannot see what the mount does on its own: cap the telescope and finder whenever the Sun is up, and stay with the mount while it moves. |
How to use it
Polar alignment. With the place set (shared with the other astronomy pages), the page shows where Polaris — or, south of the equator, σ Octantis — is on a polar-scope reticle at this second: as a clock position on the usual circle, drawn as seen through an inverting polar scope or by eye, with its hour angle and distance from the pole. Level the mount, set the latitude, turn the reticle so 12 is at the top, and put the star on the circle at that clock position with the altitude and azimuth bolts. For better than a few arcminutes, follow the drift-alignment steps (a star on the meridian for azimuth, one low in the east for altitude); the calculator turns a drift in arcseconds over some minutes into the pole error (ε ≈ 3.8 × drift ÷ (minutes × cos δ)).
Setting circles. Type a right ascension and declination (J2000 from a catalogue, or of date), or
pick an object or planet, for its altitude, azimuth and hour angle now and the local sidereal time;
or type an altitude and azimuth for the RA/Dec there. RA can be 5h35m17s, 05 35 17 or 83.82°.
GoTo. Choose the protocol — Celestron NexStar and Sky-Watcher SynScan hand controllers speak the same one; Meade LX200 is the other common one, used by Meade and many clones and adapters — connect the hand controller’s serial cable or the mount’s USB port, and press Connect. The page reads the position once a second (RA/Dec, altitude/azimuth, distance from the Sun). Pick a target from the Messier and Caldwell catalogue, the planets and the Moon, or type coordinates, then Slew, Sync (tell an aligned mount it is on the target, after centring it by hand) or STOP. Hold an arrow (or an arrow key) to nudge at the chosen rate; Escape stops everything. Try a simulated mount does all of this against a pretend mount in the page, with no hardware. Show the serial traffic logs every command and reply.
Do the hand controller’s own star alignment first; the page drives an aligned mount, it does not align it. Catalogue coordinates (J2000) are precessed to the date (JNow) before they are sent, which is what the hand controllers expect.
The protocols
| NexStar / SynScan (9600 baud, 8N1) | Meade LX200 | |
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Read position |
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Go to |
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Sync |
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Is it slewing |
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Stop |
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Nudge |
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The encoding and decoding, the command queue and a simulated mount answering both are tested in Node.
Browser support
Driving a real mount needs Web Serial: Chrome, Edge or Opera on a desktop (Windows, macOS, Linux, ChromeOS). Safari, Firefox and phones do not have it; polar alignment, setting circles and the simulated mount work everywhere.
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