Starwatch: the waxing moon passes Saturn and Mars

Starwatch chart 17 September 2018

The moon passes close to Saturn on Monday night. Look for it low in the south just after sunset. The chart shows the view at 20:00 BST. As the week progresses, the moon moves eastwards, heading past Mars on Wednesday and Thursday. This will be easy to spot as Mars is the brightest object to the moon on those nights, and the planet will be conspicuously red in colour. Also, during the week, notice how the moon changes phase. It is currently just passing its waxing first quarter phase (colloquially called a half moon). In the next seven days or so, it will rise later and later in the evening until by full moon, on 25 September, it will rise as the sun sets. The waxing half moon is termed first quarter because it occurs when the moon has completed one quarter of its orbit around Earth. After a full moon, the illumination decreases, known as waning. It will pass through another half moon phase, known as last quarter, on 2 October. A week later it will become a new moon and the cycle will begin again.