diff --git a/dwarfctl/cmd/dwarfctl/main.go b/dwarfctl/cmd/dwarfctl/main.go
index 4e0ba08..5c131e5 100644
--- a/dwarfctl/cmd/dwarfctl/main.go
+++ b/dwarfctl/cmd/dwarfctl/main.go
@@ -408,15 +408,15 @@ func cmdAstro() *cobra.Command {
 	c.AddCommand(
 		&cobra.Command{
 			Use:   "calibrate [start|stop]",
-			Short: "Start or stop star calibration",
+			Short: "Start or stop star calibration (requires starry sky + location)",
 			Args:  cobra.ExactArgs(1),
 			Run: func(_ *cobra.Command, args []string) {
 				scope, cleanup := dial()
 				defer cleanup()
 				switch args[0] {
 				case "start":
-					must(scope.StartCalibration())
-					fmt.Println("calibration started")
+					must(scope.StartCalibrationWithLocation(2.3522, 48.8566))
+					fmt.Println("calibration started (lon=2.35 lat=48.85)")
 				case "stop":
 					must(scope.StopCalibration())
 					fmt.Println("calibration stopped")
diff --git a/dwarfctl/internal/api/client.go b/dwarfctl/internal/api/client.go
index be678ac..b6d55ab 100644
--- a/dwarfctl/internal/api/client.go
+++ b/dwarfctl/internal/api/client.go
@@ -238,9 +238,16 @@ func (t *Telescope) SetFocusInfinityPos(pos int32) error {
 
 // --- Astro commands ---
 
-// StartCalibration begins star calibration.
+// StartCalibration begins star calibration. Requires lon/lat and a starry sky.
+// This is the ONLY way to home motors and get absolute positioning.
 func (t *Telescope) StartCalibration() error {
-	_, err := t.sendEmpty(CmdAstroStartCalibration)
+	_, err := t.send(CmdAstroStartCalibration, &pb.ReqStartCalibration{})
+	return err
+}
+
+// StartCalibrationWithLocation begins calibration with explicit coordinates.
+func (t *Telescope) StartCalibrationWithLocation(lon, lat float64) error {
+	_, err := t.send(CmdAstroStartCalibration, &pb.ReqStartCalibration{Lon: lon, Lat: lat})
 	return err
 }