Astro Arts' Hoshi Navi (Star Navi) is an interactive star chart for the DS. It features a guide to star names, sunrise and sunset times (as well as those for the moon), and an encyclopedia of astronomical phenomena. It's designed by Astro Arts, who operates the Astro Arts astronomy website and also publishes astronomy magazines in Japan. They seem to have an interest in sharing astronomy with the masses, so it makes sense that they'd be looking to the DS.
The original source is Famitsu in Japanese. DS Fanboy has more details in English.