Another often-discussed element of the Malta Temples is archaeoastronomy, that is, determining whether the temples were laid out according to some astronomical alignments. The basic problem with trying to nail down an alignment is the shape of the structures. They're round, and as you might imagine, trying to establish a straight alignment from a round building is difficult.
Researchers who have looked into the possible archaeoastronomy include George Agius and Frank Ventura, who looked hard and found what they called an "axis of symmetry" at some of the temples, that is to say, a line that seemed to split, say, Hagar Qim, into two (relatively) symmetrical halves. Giorgia Fodera Serio and colleagues used their lines, and discovered 26 azimuths, 20 of them between 128 and 230 degrees (or roughly between southeast and southwest). But six others, including four from Hagar Qim, showed no similarity whatsoever.
A stone recovered from the small Tal-Qadi temple has straight lines and symbols that probably represent stars and the moon. A number of the temples point toward Alpha and Beta Centauri, but not with enough accuracy to definitively say that was the intended use. Ta' Hagrat's opening might have faced the rising of Alpha Centauri in 3500 BC; and Ggantija faced the Centauri stars, especially after its original construction was rebuilt.
The Gozo Project team, however, points out that alignments which seem to point to Alpha Centauri could be interpreted as pointing to the north, to Sicily and other places, as the Maltese were longing for their central Mediterranean homelands and materials they were unable to get--obsidian and timber.
More simply, Mnajdra's entrance seems to face directly towards sunrise at the equinox, but it's the only one that does that.
Sources
Serio GF, Hoskin M, and Ventura F. 1992. The orientations of the temples of Malta. Journal of the History of Astronomy 23(2):107-119. (main source)
See the Malta Temples bibliography for more information.
