Cloud Control

Katie Curtis
Diffraction Limited's new Boltwood Portable Cloud Sensor ($350) enables you to sleep when conditions are astronomically poor, and then alerts you with an alarm when the skies clear. It's ideal for star parties and other dark-sky excursions. Each Cloud Sensor comes with a 5-by-1½-inch sensor head and control box, and batteries to power the unit for approximately 100 hours. The device works by comparing the temperature of the sky (based on the mid-infrared radiation it emits) and the ambient temperature at ground level — large differences indicate clear skies. The sensor will also alert you to deteriorating conditions, and a built-in daylight sensor can be set to sound off at twilight. You can also disable the alarm if you'd rather sleep in.

Diffraction Limited

25 Conover St.
Ottawa, Ontario, Canada K2G 4C3

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