Jigger (sand flea) infested foot. Tunga penetrans (chigoe flea or jigger) is a parasitic insect found in most tropical and sub-tropical climates. It is native to Central and South America, and has been inadvertently introduced by humans to sub-Saharan Africa. Synonyms for Tunga penetrans include Sarcopsylla penetrans, Pulex penetrates, and many others. In its parasitic phase it has significant impact on its host, which include humans and certain other mammalian species. A parasitical infestation of T. penetrans is called tungiasis.
According to data provided by the U.S. Navy Oceanography Portal (http://www.usno.navy.mil/USNO/as...), astronomical twilight lasts much longer (nearly 2 hours) during the summer compared to the winter months (only about 30-40 minutes).
Astronomical twilight occurs when the Sun is between 12 degrees and 18 degrees below the horizon. In the morning, the sky is completely dark before the onset of the astronomical twilight, and in the evening, the sky becomes completely dark at the end of astronomical twilight.