The Clava Cairns of the Central Highlands of Scotland were recognised by Aubrey Burl (1973) as largely lunar orientated. Their defining feature is a southwest orientation, as described by Audrey Shore Henshall (1972), Stuart Piggott (1982), Clive Ruggles (1999) and Richard Bradley (2000). However Balnuaran of Clava has two passage-graves which Ewan MacKie (1975) found aligned with midwinter sunset and Bradley (2016) compared this orientation with those of Maes Howe, Durrington Walls and Stonehenge. Bradley (2000) also suggested that midsummer sunrise at Balnuaran of Clava connected the central ring- cairn with a separate monument at Mains of Clava, neither monument being directly opposite Balnuaran's passage-graves. This posed questions about the comparative roles of ring-cairns and passage-graves, light versus dark, potentially summer versus winter. This paper considers the major lunar limit, by exploring the topography of the region's river systems which are orientated northeast-southwest. Skyscape archaeology fieldwork focused on the southern horizon and the major lunar limit at one hundred and thirty eight locations. One hundred riverside (non-cairn) locations constituted the expected baseline for data, plus thirty eight cairn sites. Each exhibited a lunar horizonal event during major lunar limit years, ranging from normal to invisible. Most Clava cairns were located at sites where interesting lunar phenomena were visible, such as skimming, disappearing and emerging, despite the bulk of the terrain being in midsummer full moon darkness (non-visibility) during major limit years. Balnuaran of Clava was significantly different, exhibiting midwinter sunset, while experiencing midsummer full moon darkness, confirming Ruggles' (1999) description of the site as exceptional.