People in Las Vegas Need to Travel to see this Event
Despite what many people seem to think, the May 20, 2012 annular eclipse is not visible from Las Vegas, Nevada. The narrow band of the moon's shadow tracks close to Vegas, but to the north. Those in the resort city will not see the annular eclipse. They will see a very highly eclipsed sun, but it is not as spectacular as the real annular solar eclipse event.
Those in Las Vegas in the evening of May 20, should proceed north from the city at least 50 miles for a better experience. In fact, the best show will be substantially farther. The map of the annular eclipse path was used to determine where Las Vegas residents should go. Travelling on I-15, an annular eclipse viewer should proceed past St. George, Utah, stopping about 10 miles short of Cedar City, Utah. While St. George does experience the full annular eclipse, the duration is longer at the exact center of the eclipse path. North of St. George, driving on I-15, take exit 42, heading towards Kanaraville, Utah. The optimal viewing point, for maximum duration, is just south of the town. Anywhere in this vicinity, however, will provide an excellent view of the eclipse, far better than in the city of Las Vegas.
The annular eclipse occurs when the moon passes directly in front of the sun. This can only happen on a New Moon, such as May 20, 2012. Usually at New Moon, the moon travels above or below the sun and no eclipse happens at all. Other times, the moon glances the sun. This causes a partial solar eclipse. If the moon passes directly in front of the sun, a total eclipse, or an annular one, occurs. The difference occurs depending on the distance of the moon to the earth, which is slightly variable. If the moon is closer to the earth, a total eclipse happens. If it is farther, then an annular solar eclipse happens. On May 20, 2012, the moon is just a day past its closest approach to the earth so a total eclipse does not happen.
Since the moon is so small compared to the earth, and since the sun is so far away, we are lucky that solar eclipses happen at all. The moon is just large enough to cover the sun, sometimes. If the conditions are just right, a total eclipse happens. So why does the May 20 eclipse not visit Las Vegas? The moon is nearly large enough to cover the sun and throw a shadow onto the earth's surface, but it is a very small shadow. Las Vegas is just outside of the shadow area. That means that the city does not see the annular eclipse and residents there have to travel if they want to see the main event. Those who stay in Las Vegas will see a substantially eclipsed sun, but it will be a partial eclipse for them.
Imagine that you hold out your thumb and pass it between you and a light bulb, shielding you from the light. Try this with one eye closed. As your thumb moves between the bulb and your eyes, the amount of light you see is greatly diminished. When your thumb covers the bulb, all of the light is blocked and you get a total eclipse of the source. Now close your eye and open the other. You will now see the light and your thumb will be slightly away from the bulb. That is the difference between the cities of Reno and Las Vegas. Reno gets the annular eclipse while Las Vegas does not. Using the your thumb shielding the light, with only one eye open, do it again but let your thumb pass but don't totally obscure the light source. You have created a partial eclipse, just like Las Vegas will see. Cover the whole light source and you get Reno's annular elipse event. Of course, you would have to hold your thumb in place for about 4 and a half minutes to simulate the duration of the event at Reno.
Many other cities are just outside the eclipse path as well. San Francisco, Denver and Dallas do not see the event. Instead, they get various degrees of partial solar eclipses. Lubbock, Texas, does see the event, but it occurs right at sunset. Viewers there will need to have a very clear view to the west if they hope to be lucky. Watch the weather, though.
Obviously if the weather is cloudy, the annular eclipse will not be visible, nor will Las Vegas see the partial eclipse. Luckily this eclipse event passes across the western United States which is famous for sunny weather. The time of year even offers a good chance of clear skies. This is less true to the west in places such as Eureka, Medford and Redding. To the east, it may be clearer. One thing to note is that the eclipse will cause the weather to stall out. If there are clouds moving in your area, but the sun is still visible, they may stop, for a while. You could be lucky and have the clouds hold off, allowing you to view the annular phase of the eclipse. The reason is that the sun will have less heat while the moon eclipses the light. Since the sun drives most weather, including wind, there is not as much weather during the time immediately before the eclipse. The opposite holds true as well. If you hope that the wind moves clouds away, giving you a better view of the eclipse, it may not work.
Remember that this eclipse is not a total solar one. Proper eye protection is a must during all phases of the May 20 event. Even when the sun is as eclipsed as it is going to be, there is enough light escaping to be very dangerous. Proper solar filters are needed to ensure safety. A digital camera can also be used as it allows indirect viewing of the event. Protect your eyes, and those of your family and friends. It is better to watch the event on the Internet than to suffer eye damage that hinders sight.