In less than a month’s time, one of the finest solar eclipses since 1918 will pass across the United States. Weather permitting, the entire continent will be able to see the moon pass in front of the sun on 21 August 2017, as the total solar eclipse takes place.
Solar eclipse 2017: What time is the eclipse?
The total solar eclipse will start near Lincoln City, Oregon, at 10.15am PDT (1.15pm EDT) and totality will end at 2.48pm EDT near Charleston, South Carolina. It will last around one hour and 40 minutes.
Solar eclipse 2017: Where will the eclipse be visible?
The total eclipse will only be visible over the US. NASA has produced an animated video showing the path of the eclipse. It shows the umbra (depicted as a black oval), penumbra (concentric shaded ovals) and the path of totality in red. The sun is also shown in a number of locations.
The path of totality is around 70 miles wide and will cross from West to East. Its longest duration will be over Illinois, where the sun will be covered for two minutes and 40 seconds.
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Solar eclipse 2017: What is a total eclipse?
The sun’s diameter is 400 times wider than the moon’s but is 400 times farther away. This geometry results in the sun and moon seeming to appear the same size when looked at from Earth. As they line up, the moon blocks the sun’s surface. This line-up occurs once every 12 to 18 months.
Partial solar eclipses occur when the alignment of the moon blocks only part of the sun, and these can occur more frequently.
During a total eclipse, the alignment occurs in such a way in which the sun’s outer atmosphere, known as the corona, appears to radiate around the shadow created by the moon. It looks like a ring of bright light bursting from the lunar disk.
Solar eclipse 2017: Why is the August eclipse so significant?
Beyond looking beautiful, and their rarity, total eclipses can be used for scientific purposes. In previous years, it has helped astronomers unlock the secrets of general relativity, coronal mass ejections, and the sun’s temperature.
“An eclipse teaches us so many things, but the 2017 eclipse is especially unique because of the uninterrupted land masses it will pass over,” said Dr Lika Guhathakurta, an astrophysicist at NASA Headquarters in Washington. “This will allow us to maximise our chance to collect data and connect the shadow of the moon to Earth science.”
The NASA-funded Global Learning and Observations to Benefit the Environment, or GLOBE, Program recently released an app that people watching the eclipse can use to gather scientific data. Each phone running the app will act like a ground sensor, feeding back information about the eclipse to create a simulation of this year’s eclipse and build a so-called 3-D radiative transfer model.
You can download the app from the GLOBE Observer site. To gather data you’ll need to register to become a citizen scientist and use a thermometer to measure air temperature. The app will guide you through the steps for collecting the data points and your observations will be recorded on an interactive map.
For example, studying the corona and its role in space will help astronomers understand the relationship between Earth and the sun, and offer clues to future space missions.
Solar eclipse 2017: How to watch the eclipse safely
NASA advises watching the solar eclipse through a filter that minimises ultraviolet, visible and infrared light. Eclipse glasses can be bought online. The only time it is safe to look at the eclipse is during the phase of totality, when the moon fully obscures the sun, but this lasts for seconds so it is better to watch through a filter at all times.