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TelescopeRightAscensionRate Property
The right ascension tracking rate offset from sidereal (seconds per sidereal second, default = 0.0)

Namespace: ASCOM.DriverAccess
Assembly: ASCOM.DriverAccess (in ASCOM.DriverAccess.dll) Version: (
public double RightAscensionRate { get; set; }

Property Value

Type: Double


This property, together with DeclinationRate, provides support for "offset tracking". Offset tracking is used primarily for tracking objects that move relatively slowly against the equatorial coordinate system. It also may be used by a software guiding system that controls rates instead of using the PulseGuide method.

NOTES: The property value represents an offset from the currently selected TrackingRate.

  • If this property is zero, tracking will be at the selected TrackingRate.
  • If CanSetRightAscensionRate is False, this property must always return 0.
  • The property value is in in seconds of right ascension per sidereal second.
  • To convert a given rate in (the more common) units of sidereal seconds per UTC (clock) second, multiply the value by 0.9972695677 (the number of UTC seconds in a sidereal second) then set the property. Please note that these units were chosen for the Telescope V1 standard, and in retrospect, this was an unfortunate choice. However, to maintain backwards compatibility, the units cannot be changed. A simple multiplication is all that's needed, as noted. The supported range of this property is telescope specific, however, if this feature is supported, it can be expected that the range is sufficient to allow correction of guiding errors caused by moderate misalignment and periodic error.
  • If this property is non-zero when an equatorial slew is initiated, the telescope should continue to update the slew destination coordinates at the given offset rate. This will allow precise slews to a fast-moving target with a slow-slewing telescope. When the slew completes, the TargetRightAscension and TargetDeclination properties should reflect the final (adjusted) destination. This is not a required feature of this specification, however it is desirable.
  • Use the Tracking property to enable and disable sidereal tracking (if supported).

See Also