Sources used for ‘The Bortle scale and what we lose behind the light of the night’

• ASTROPHOTOGRAPHY LENS (2024) The Bortle scale. [Online image] Available from: https://astrophotographylens.com/blogs/astro/bortle-scale
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• DARKSKY (2024) Five principles for responsible outdoor lighting. [Online] Available from: https://darksky.org/resources/guides-and-how-tos/lighting-principles/
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• FROMMERT, H. and KRONBERG, C. (2013) Messier object data, sorted by apparent visual magnitude. [Online] Messier SEDS. Available from: http://www.messier.seds.org/dataMag.html#:~:text=1%3DOpen%20Cluster%2C%202%3D,Patch%2C%20C%3DBinary%20star.
• GRUBISIC, M. HAIN, A. BHUSAL, P. DOMINONI, D. M. GABRIEL, K. M. A. JECHOW, A. KUPPRAT, F. LERNER, A. MARCHANT, P. RILEY, W. STEBELOVA, K. GRUNSVEN, R. H. A. ZEMAN, M. ZUBIDAT, A. HÖLKER, F. (2019) Light Pollution, Circadian Photoreception, and Melatonin in Vertebrates. Sustainability. [Online] 11 (22). Available from: https://www.mdpi.com/2071-1050/11/22/6400
• HEGGIE, D. (2023) The Gegenschein. [Online] The astronomical society of Edinburgh. Available from: https://www.astronomyedinburgh.org/2023/02/23/the-gegenschein/
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• KEINATH, S. HÖLKER, F. MÜLLER, J. RÖDEL, M. (2021) Impact of light pollution on moth morphology–A 137-year study in Germany. Basic and applied ecology. [Online] 56 (Nov.). Available from: https://www.sciencedirect.com/science/article/pii/S1439179121000967
• MESSIER OBJECTS (2015) Messier 4. [Online] Available from: https://www.messier-objects.com/messier-4/
• MESSIER OBJECTS (2015) Messier 5. [Online] Available from: https://www.messier-objects.com/messier-5/
• MESSIER OBJECTS (2015) Messier 7: Ptolemy’s cluster. [Online] Available from: https://www.messier-objects.com/messier-7-ptolemys-cluster/
• MESSIER OBJECTS (2015) Messier 15: Great Pegasus cluster. [Online] Available from: https://www.messier-objects.com/messier-15-great-pegasus-cluster/
• MESSIER OBJECTS (2015) Messier 22: Sagittarius cluster. [Online] Available from: https://www.messier-objects.com/messier-22-sagittarius-cluster/
• MESSIER OBJECTS (2015) Messier 31: Andromeda galaxy. [Online] Available from: https://www.messier-objects.com/messier-31-andromeda-galaxy/
• MESSIER OBJECTS (2015) Messier 33: Triangulum galaxy. [Online] Available from: https://www.messier-objects.com/messier-33-triangulum-galaxy/
• MESSIER OBJECTS (2015) Messier 42: Orion nebula. [Online] Available from: https://www.messier-objects.com/messier-42-orion-nebula/
• MESSIER OBJECTS (2015) Messier 44: Beehive cluster. [Online] Available from: https://www.messier-objects.com/messier-44-beehive-cluster/
• MESSIER OBJECTS (2015) Messier 45: Pleiades. [Online] Available from: https://www.messier-objects.com/messier-45-pleiades/
• SILVA, A. D. VALCU, M. and KEMPENAERS, B. (2015) Light pollution alters the phenology of dawn and dusk singing in common European songbirds. Royal society. [Online] 370 (1667). Available from: https://royalsocietypublishing.org/doi/full/10.1098/rstb.2014.0126
• WIKIPEDIA (2025) Airglow. [Online] Available from: https://en.wikipedia.org/wiki/Airglow
• WIKIPEDIA (2025) Bortle scale. [Online] Available from: https://en.wikipedia.org/wiki/Bortle_scale
• ZHANG, B. ZHANG, H. JING, Q. WANG, J. (2020) Light pollution on the growth, physiology and chlorophyll fluorescence response of landscape plant perennial ryegrass (Lolium perenne L.). Ecological indicators. [Online] 115 (Aug.). Available from: https://www.sciencedirect.com/science/article/abs/pii/S1470160X2030385X

The images used were sourced from Astrophotography lens and edited by Natalie Peirce.