Mac computers have a system feature called Gatekeeper, which keeps users from automatically opening any app not downloaded directly from the Mac App Store. However, they do provide a fairly easy way to open apps like Astro Gold with only a few extra steps.

If you so get a message telling you that the app cannot be opened, then click OK on the message to close it. Then
open your Downloads folder and find the Astro Gold app you are trying to run. Drag Astro Gold into your Applications folder. Now, either Control-click, or right-click, the Astro Gold app you just put in Applications. This will give you a menu, and at the top of that menu, click the word Open. You should now get a message saying “Astro Gold” is from an unidentified developer, and are you sure you want to open it? Click on the Open button on that message. Astro Gold should open now, and it should open without a problem any other time you want to run it as well.