Point often for the first 2–3 hours after sunset because the pointing will shift as the temperature of the telescope changes (thermal pointing shifts). Repoint no later than an hour after the initial pointing. Repoint every 2.5–3 hours thereafter.

Beam switching with the wobbling Secondary mirror may give more consistent results, especially if the weather is marginal. Use a short subscan integration time because there are four subscans at each point. Position switching is also possible.

Before pointing,

The pointing examples use 12CO(2-1) and beam switching.

Line pointing

There are many more line sources – typically evolved stars – than bright continuum sources. But it may be necessary to tune the receiver to a bright line. The example uses 12CO(2-1) and beam switching. Position switching is also possible.

If the line is not centered in the spectrometer or if there are lines in the baseline windows, take a spectrum prior to pointing to determine the line position and the line free baseline windows. This may be difficult if the pointing is far off.

For standard sources, it is good practice to take a reference spectrum just after pointing as a calibration comparison.

Continuum pointing

The bright planets, Mars, Jupiter, and Saturn, are good sources. Uranus and Neptune may be (very) difficult.

It is good practice to take a reference spectrum of the planet just after pointing to check the beam efficiency.