APA (7th ed.) Citation

Moulton, F. R. (2010). An Introduction to Astronomy. Project Gutenberg.

Chicago Style (17th ed.) Citation

Moulton, Forest Ray. An Introduction to Astronomy. Project Gutenberg, 2010.

MLA (9th ed.) Citation

Moulton, Forest Ray. An Introduction to Astronomy. Project Gutenberg, 2010.

Warning: These citations may not always be 100% accurate.