Image of the meadowlark

Eastern meadowlark • Photo by synspectrum (CC BY 2.0)

Image of trefoil

Trifolium dubium (lesser trefoil) • (CC BY SA 3.0)

Image of star atlas

17th century star atlas (Public Domain)

Image of interference pattern

A simulated interference pattern • Timm Weitkamp (CC BY 3.0)

Image of Halley's Comet

Halley's Comet, as seen in March 1986 • NASA/W. Liller (Public Domain)