Seeing a rainbow in Hawaii is now easier than just being in the right place at the right time.

A University of Hawaii professor and a local businessman recently produced a free smart- phone app that predicts the most likely spots to see rainbows, based on the angle of the sun and moisture in the air.

The RainbowChase app gives users an idea of where rainbows are most likely to be seen, based on their location in real time.

“You could say the goal of the app is to bring more rainbows into your life,” the app’s co-creator Steven Businger said in a video in the app program.

Businger, an atmospheric sciences professor at UH’s School of Ocean and Earth Science and Technology, created the app with Hawaii businessman Paul Cynn and help from local software development firm Ikayzo.

The app to date is limited to Oahu, though the developers have plans to make it available for use on the neighbor islands, followed by the mainland and then Asia and Europe.

Other ideas include expanding the technology to calculate where halos, coronas and brilliant sunsets can be found, based on weather data and a user’s location.

One feature in the app allows users to submit photos they take of rainbows to RainbowChase for possible showcasing in a gallery in the app.

Businger said one limitation on the effectiveness of the app is the presence of clouds blocking the sun from a user’s location, though this is something the developers are working to address with a future update.

Some extra knowledge about rainbows also can help finding them.

One tip offered by Businger: To see a rainbow on flat ground, the sun must be within about 40 degrees of the horizon. Bus­in­ger also said the height of rainbows will be tallest with the sun at its lowest point to the horizon.

The app, which works with iOS and Android operating systems, will remain free, according to Businger.