This children's museum houses four floors of constellations, ancient astronomy, space science and observatories. Although fun, there is a dearth of English-language content. More English-friendly attractions (at an extra charge) are the IMAX and 3D theatres. Cosmic Adventure is a space journey simulator that trundles pod riders past the planets of the solar system. You can sky- and star-gaze through the optical telescope on the 4th floor for free (10am to noon and 2pm to 4pm Tuesday to Sunday, and 7pm to 9pm Saturday).
This place is very popular with school trips on weekdays. It's a 1km walk from Shilin MRT across busy roads. Alternatively take the R30 from outside Exit 1 (cross the road).