The present invention relates to a method for a low cost Planet vector Sensor based on imaging atmospheric oxygen emission at 762 nm or at 557.7 wavelengths using either CMOS, CCD or arrays of single photon avalanche diodes (SPADs). In both daytime and night time, there is continuous emission at 762 nm wavelength due to atomic oxygen recombination or excitation. Even if the emission at the limbs is 100 times stronger in the day than at night, there is ample unambiguous signal for the operation of the sensor according to the present invention using this wavelength if measured with an appropriate detector (82) and an adapted algorithm to determine the Planet vector.