1. What help us to know the world around us
., FAQ-ANS, August 13, 2021. https://faq-ans.com/en/Q%26A/page=ef9b919ba475fd24194141634399321e
2. Observing the World Around Us
, An introduction for teachers and parents. https://hea-www.harvard.edu/ECT/pdf/ECT.pdf
3. 20 Major current environmental problems
. https://www.conserve-energy-future.com/15-current-environmental-problems.php
4. Woo, M.
, Discovering new worlds, Caltech media relations. October 20, 2010. https://www.caltech.edu/about/news/discovering-new-worlds-1811
5. New Worlds
, New Horizons in Astronomy and Astrophysics. Panel reports, The National Academies Press, Washington, DC: 2010. https://www.nap.edu/catalog/12982/panel-reports-new-worlds-new-horizons-in-astronomy-and-astrophysics