Instructions

Courtesy of the Raspberry Pi Foundation
ASTRO PI: SOFTWARE SETUP
This guide assumes you have an SD card loaded with NOOBS/Raspbian. If
not, see the Downloads section to download NOOBS/Raspbian and use
the NOOBS setup guide for help with installation.
Connect your Sense HAT and boot it up.
ASTRO PI DRIVER INSTALLATION
Ensure your Pi is connected to the internet, then run the following
command (from the command prompt or a Terminal window) to download
and start the Astro Pi installation script:
wget -O - http://www.raspberrypi.org/files/astro-pi/astro-pi-install.sh --
no-check-certificate | bash
This will take about 5 minutes on a Pi 2 and about 15 to 20 minutes on a Pi
1. When it's finished you'll see the following message:
You must reboot to complete the Astro Pi installation
Type:
sudo reboot
and press Enter when ready
Reboot the Raspberry Pi to complete the installation:
sudo reboot
The rainbow pattern on the LED matrix should now turn off during boot up.