Whilst there is a growing interest in people's relationship with the natural world, much of the literature in this area tends to focus on daytime behaviour. There is far less research that attempts to understand the importance of people's relationship to natural environments at night and particularly towards the night sky. Therefore, the purpose of this study was to design, develop and validate a new measure - the Night Sky Connectedness Index (NSCI). The items of the NSCI were created and based on relevant theory, similar types of measures, and stakeholder consultation – for both the generation and selection of items. The psychometric properties were assessed using a sample of 406 people from the general population – with any level of interest in the night sky - and of these 115 completed a test-retest follow-up survey. Exploratory Factor Analysis and reliability testing resulted in a 12-item measure with two subscales: Connection to, and Protection of the night sky. The NSCI demonstrated good to excellent internal consistency for the overall scale and for each of its subscales and shows strong test-retest reliability. There was also strong evidence for the scale's convergent, discriminant and construct validity. In addition, the findings indicated that a greater connection to the night sky was significantly and positively related to a person's mental health and happiness. Our research also suggests that those people who live in more light-polluted areas are less connected to the night sky and feel less likely to protect it. The NSCI may be useful when, (i) investigating pro-environmental and conservation behaviour, (ii) assessing the efficacy of strategies or interventions aimed at reducing light pollution, (iii) helping to restore the human-night sky relationship, (iv) informing policy and responsible lighting use, and (v) rewilding our night skies to protect our natural environment and cultural heritage.
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