Source: USGS Landsat
All 8 million Landsat scenes are available to download from EarthExplorer, GloVis, and the LandsatLook Viewer.
As the world’s longest continuously acquired collection of space-based, moderate-resolution land remote sensing data, the USGS Landsat archive adds over 1,100 scenes each day.

STELLA: A DIY Handheld Scientific Instrument
If you are looking for a do-it-yourself (DIY) handheld spectrometer, you need to meet STELLA. STELLA (Science and Technology Education for Land/Life Assessment) is a portable scientific instrument developed by