Determining the pseudo magnitude of the o Oph A star using Iris 5.59 software observed from the Astronomy Laboratory, Department of Physics, Faculty of Mathematics and Natural Science, State University of Malang

o Oph A star is a star in the Ophiuchus star cluster. o Oph A stands for omicron Ophiuchi A. Ophiuchus is a zodiac between Scorpio and Sagittarius in the current era, the 9th zodiac is calculated sequentially from Aries and finally, the 13th is Pisces. A magnitude scale is a unit for measuring the brightness of a star. The magnitude of stars that can be observed from the earth is called pseudo magnitude. Observation and data collection of o Oph A star was held on Monday, September 30th, 2019, at 18:47 West Indonesian Time at the Astronomy Laboratory, Physics Department, FMIPA, State University of Malang with position (7°57'38.7"S 112° 37'09.4"E) which coincided around the planet Jupiter. The method used is a descriptive method with the star photometry technique, which is assisted by the Celestron 2000 telescope, sky sensor 2000, and a digital camera 8 MP to observe and take images of the conditions around the o Oph A star. Then identify the results of these images using the Stellarium Mobile v1.25 application. After obtaining information about the pseudo magnitude of the e Oph star as a standard star in the Stellarium Mobile v1.25 application that is equal to 3.25, then analyzed with Iris 5.59 software with a constant magnitude of 16.548. A pseudo magnitude of the o Oph A star is obtained (5.085±0.00) with a measurement error of 0.29%.