Star Walk 2by Vito Technology Inc. is one of the best—if not the best—stargazing apps in the App Store. Thursday, Star Walk 2 got slashed to zero bucks as part of Apple’s Free App of the Week promotion in the App Store.

Winner of Apple Design Award, the app taps your iPhone’s sensors and the GPS to determine the exact position of stars, planets, constellations, comets, ISS, satellites, star clusters, nebulae and meteor showers in the night sky.

Star Walk 2 iPhone screenshot 001

The app features crisp Retina graphics with augmented-reality style HUD that renders the sky over live camera feed, responding precisely to the movement of your device without requiring Internet connection.

App Store editors explain:

Discover the wonders of the universe with this powerful, easy-to-use astronomy toolkit. Just aim your device to view the real-time positions of planets, stars, constellations and more in stunning interactive map. Zoom in to explore Wikipedia articles, 3D models and other media related to your favorite celestial bodies.

The app normally sells for $2.99 and has never been free in the App Store since its August 2014 debut until today. If you’re interested in Night Sky 2,read my review.

Star Walk 2 iPhone screenshot 002

Star Walk 2 highlights:

Compared to the original Night Sky, Night Sky 2 has a simpler user interface optimized for Retina screens, atmospheric visual and sound effects and soundtrack, beautifully handcrafted artwork for constellations inspired by minimalist low-poly art and additional detailed 3D models of celestial bodies.

In addition to stock celestial bodies, objects like planetary nebulae, constellations, dwarf planets, comets and asteroids, man-made satellites, as well as layer-by-layer planets and missions, are available as In-App Purchases.

https://www.youtube.com/watch?v=KKoDvxIYLTs

In its most recent update, the app has added high-definition Martian surface data and missions to Mars.

The 124-megabyte app requires an iPhone, iPod touch or iPad with iOS 7.0 or later. Night Sky 2 is optimized for the iPhone 5/5s/5c, iPhone 6 and iPhone 6 Plus and currently lacks a WatchKit component.

Grab Star Walk 2 at no charge in the App Store.