launch agent for periodically running xplanet

xplanet.plist

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<!--Put this in ~/Library/LaunchAgents and launchctl load it. Note that this
    doesn't seem to work anymore in Snow Leopard.-->
<dict>
    <key>Label</key>
    <string>xplanet</string>
    <key>Nice</key>
    <integer>5</integer>
    <key>ProgramArguments</key>
    <array>
        <string>/usr/local/bin/xplanet</string>
        <string>-num_times</string>
        <string>1</string>
        <string>-body</string>
        <string>major</string>
        <string>-random</string>
        <string>-range</string>
        <string>20</string>
        <string>-label</string>
        <string>-labelpos</string>
        <string>-15+680</string>
    </array>
    <key>RunAtLoad</key>
    <true/>
    <key>StartInterval</key>
    <integer>3600</integer>
</dict>
</plist>