The NASA eclipse live stream has begun. Watch it here

The finest total solar eclipse since 1918 will pass across the United States today. Weather permitting, the entire coast-to-coast of the US will have an opportunity see the moon pass in front of the sun from the morning of 21 August 2017 to mid-afternoon. 

Solar eclipse 2017: What time is the eclipse today in the UK?

In the UK today, the eclipse will be visible shortly after 7.30pm BST and reach its maximum half an hour later, at 8pm BST – although the chances of seeing it are slim.

In the US, 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.

Location	Partial eclipe begins	Total eclipse time
Salem	09:05 am PDT	10:18 am PDT
Idaho Falls	10:15 am MDT	11:33 am MDT
Casper	10:22 am MDT	11:43 am MDT
Lincoln	11:37 am CDT	1:03 pm CDT
Sabetha	11:38 am CDT	1:05 pm CDT
Jefferson City	11:46 am CDT	1:14 pm CDT
Carbondale	11:52 am CDT	1:21 pm CDT
Hopkinsville	11:56 am CDT	1:25 pm CDT
Nashville	11:58 am CDT	1:28 pm CDT
Talulah Falls	1:07 pm EDT	2:37 pm EDT
Columbia	1:13 pm EDT	2:43 pm EDT
Charleston	1:16 pm EDT	2:47 pm EDT

Timeanddate.com additionally has an solar eclipse database that reveals the exact time for the vast number of extra locations where the eclipse will be visible. 

Solar eclipse 2017: Watch the NASA eclipse live stream

The UK will only experience a partial eclipse, and predominantly in northern regions, if the weather conditions are optimal. However, the Met Office forecast shows there will be rain in the northwest, with clouds and drizzle this morning, turning into heavy rain. It will be largely cloudy and humid across the UK with widespread hill and coastal fog. This makes viewing the solar eclipse unlikely. 

People in the UK can still watch the eclipse online, though. NASA will be broadcasting a three-hour live stream of the event from 1pm to 4pm EDT (6pm BST to 9pm BST) on NASA TV, with preview shows beforehand. We have embedded the stream below.

There will also be live feeds from NASA aircraft, balloons, and the International Space Station. The three-hour program, called “Eclipse Across America: Through the Eyes of NASA” will give real-time coverage of the event as the eclipse moves from coast to coast.

On Twitter, the eclipse will be live-streamed via the Chasing Eclipse 2017 feed, which features a handy countdown, and it will be available via Facebook Live. You can follow the latest eclipse news and pictures using the #eclipse hashtag. 

Solar eclipse 2017: Where to watch the eclipse?

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.

The National Solar Observatory has predicted that the solar corona, which looks like a halo around the sun, during the August eclipse appear “fuzzy” and predicts it will, at first glance, resemble a sprinkle of iron filings around a bar magnet, or a butterfly shape. Viewers are then expected to see faint, straight structures sticking out from the north and south poles of the sun – known as polar plumes – as well as brighter “bulbs” of material closer to the equator called helmet streamers.

Solar eclipse 2017 map

NASA has released a series of maps and animations to reveal the path of the total solar eclipse. The map above shows the path of the moon’s umbral shadow — also known at the path of totality — during the total solar eclipse 2017. It additionally shows the so-called obscuration, which is when a fraction of the Sun will be covered by the moon, outside of the umbral path. 

The map below shows the shapes of the umbra and penumbra in a shapefile. NASA has also released solar eclipse maps that show how the events were recorded in the past, and what the paths of totality looked like. 

Solar eclipse 2017: What is a total solar 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: 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.

This is because the rods and cones in the retina are extremely sensitive to light and even a small ray of sunlight can hit thousands of these light-sensitive cells. During the day, your iris contracts to stop too much light from entering the eye and hitting the retina. If you’ve ever looked straight at the sun, you’ll know it can leave spots in front of your eyes. Gazing at it for too long, such as during the eclipse, can damage your retinal cells and these spots can become permanent.

NASA’s guidelines state that eclipse viewing glasses must have certification information with a designated ISO 12312-2 international standard, feature the manufacturer’s name and address and not be used if they are older than three years, or are scratched. Regular sunglasses do not provide enough protection and should not be used to look at the sun during the eclipse. 

To make sure children get to experience the wonder of the solar eclipse, Google recently partnered with Mystery Science to help millions of US kids across what the pair is calling the Great American Total Solar Eclipse. This includes giving millions of solar eclipse glasses being distributed to libraries, free of charge. Google has also paid for 15,000 eclipse glasses to be shipped directly to schools. 

“Going to the moon, exploring the surface of mars, or seeing a total solar eclipse across the US for the first time in a century are amazing moments that can inspire a whole new generation of explorers and scientists,” said Calvin Johnson, Program Manager at Google for the Eclipse Megamovie project. “Our collaboration with Mystery Science ensures that educators have the resources needed to drive and encourage the curiosity of students and push our understanding of the universe to another level.”

An alternative is to watch the eclipse through a pinhole projector. This involves putting a small hole in a piece of paper and holding it up to the sun. Sunlight can then be streamed through this small hole onto a makeshift screen, such as a piece of paper or a wall. If you watch this ‘screen’, you can see the eclipse without looking directly at the sun. 

More details about watching the eclipse safely can be found on NASA’s FAQ.

Solar eclipse 2017: Make your own pinhole camera

If you can’t find a pair of solar eclipse glasses, you can make a pinhole camera instead using white card (or a cereal box), tin foil, tape and a pin.  

Cut a square into the middle of one of your pieces of card and tape tin foil over this hole. Use a pin to make a small hole in the foil. With the sun behind you, hold up the card (with the foil facing up) and the image of the sun will be projected onto the second piece of card on the floor. To make the projection more defined, place the second piece of card in a shadowed area.  

Solar eclipse 2017: Why is the August solar 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: The scientific impact

In total, NASA is funding 11 ground-based science investigations during the total solar eclipse, with three set up to study the ionosphere. The ionosphere is an ionised, “electrified” layer of Earth’s atmosphere which grows and shrinks in line with changing solar conditions. It stretches from between 50 and 400 miles above Earth’s surface. Changes to the area of the lower atmosphere, or space weather, can create disruptions in the ionosphere which, in turn, interfere with our communication and navigation signals.

The total solar eclipse will cause a sudden, but temporary, drop in the amount of extreme ultraviolet radiation hitting Earth’s atmosphere from the Sun. This is expected to “trick” the ionosphere into thinking it’s nighttime, at which point scientists expect it to relax. 

Greg Earle, an electrical and computer engineer at Virginia Tech in Blacksburg, Virginia, said: “This is the best eclipse to see [and] we’ve got a denser network of satellites, GPS and radio traffic than ever before. It’s the first time we’ll have such a wealth of information to study the effects of this eclipse; we’ll be drowning in data.