United States citizens are preparing for a "once-in-a-lifetime" event - the solar eclipse which is expected to occur on Monday night. During the eclipse, the moon will completely hide the sun and cast a shadow 100 kilometers (62 miles) wide.

The eclipse's path will cross the US mainland from northwest to southeast. States located near the path of totality will experience a partial eclipse.

Each location in the path of totality will view the complete eclipse for approximately 2 minutes and 40 seconds. According to scientists, the moon's shadow will arrive in Oregon moving at a speed of 4,000 kilometers per hour (2485.5 miles per hour). The first Oregon residents will experience the eclipse at 10:15a.m. local time, and end in South Carolina at 2:49p.m. local time.

Complete solar eclipses are much more rare than lunar eclipses, which occur on average once every 12-18 months. However, each solar eclipse lasts only a few minutes and is visible from only a small portion of the earth's surface. Monday's eclipse will only be visible from the United States.

This is the first time since 1918 that a solar eclipse will cross the entire US mainland. It's also the first time since 1776 that a solar eclipse will cross only the United States, without touching any other country.

US citizens and tourists preparing to view the eclipse must wear sunglasses offering UV protection; glancing at the sun even for a second during an eclipse can cause permanent eye damage.