This paper presents a new astronomy self-efficacy instrument, composed of two factors; one relating to learning astronomy content, which we call astronomy personal self-efficacy, and the other relating to the use of astronomical instrumentation, specifically the use of remote robotic telescopes for data collection. The latter is referred to as the astronomy instrumental self-efficacy factor. The instrument has been tested for reliability and construct validity. Reliability testing showed that factor 1 had a Cronbach's [alpha] of 0.901 and factor 2 had a Cronbach's [alpha] of 0.937. Construct validity was established by computing one-way analyses of variances, with the p value suitably protected, using independent variables peripherally related to the constructs. These analyses demonstrate that both scales possess high construct validity. The development of this astronomy specific instrument is an important step in evaluating self-efficacy as a precursor to investigating the construct of science identity in the field of astronomy