The American solar eclipse is less than a fortnight away. It will be visible across the United States during the morning and early afternoon of Monday 21 August. If you’ve never seen a total eclipse of the sun, the chances are that you are going to turn to the internet for some tips on how to make the most of the opportunity. And you are going to find so much advice that – however well meaning – it is going to set your head spinning.
It’s a minefield of jargon such as first contact and umbra, and of things to look for like shadow bands and Bailey’s beads.
NASA posted a video about it on Twitter: #Eclipse2017 happens in less than a month--Aug. 21, 2017!
In trying to do everything you risk seeing nothing. It is no exaggeration to say that a total eclipse of the sun is one of the most extraordinary natural phenomena it is possible to see.
So do yourself a favour and just soak it up.
To enjoy it, there are only three things you need to do:
#1 — Get to the track of totality
Totality is the central moment of the eclipse. It is when the moon completely covers the sun.
The track of totality is the locations on the Earth where the total eclipse can be seen. Make no mistake, you have to be on the track of totality to see the total eclipse.
NASA released an extremely accurate map of the top places to spot / image by Nick Hennen / source Twitter.com
Nothing compares to totality. If you are a little way off and seeing a 95% partial eclipse, do not think that you will be experiencing 95% of a total eclipse. It simply does not work like that. Only if you are in the track of totality will the sky go dark and the beauty appear.
On 21 August, the track of totality is roughly 70-mile (113km) wide and moves from the west coast to the east coast. It starts near Salem, Oregon, and finishes near Charleston, South Carolina.
The eclipse begins in Salem at 9:05am PDT. The moon then takes over an hour to move across the sun and so totality starts at 10:18am PDT. In Charleston, the eclipse begins at 1:16pm EDT, with totality coming along at 2:46pm.
So get somewhere on the track. Once there, put out your deck chair, sit back and relax. You have made it, you are going to witness a total eclipse. And if the sky is clear, what you are going to see will make your jaw drop.
NASA released an extremely accurate map of the top places to spot the 2017 solar eclipse:
#2 — Wear eclipse glasses
Never look at the sun with unprotected eyes. I cannot stress this enough. If you look directly at the sun with your naked eyes or through any kind of unshielded binoculars or telescope you could permanently damage your eyesight.
Eclipse glasses are widely available. They consist of a black polymer material mounted in cardboard glasses that hook over the ears. They should be worn whenever you look at the sun.
When looking at the sun, as these people did for the Indonesia eclipse of 2016.
When totality begins, and you are plunged into darkness, then you can take your glasses off. At this point, the sun is no longer visible because the moon is blocking its light. As soon as the sun returns, put them on again.
Do not use sunglasses, smoked glass or a welder’s helmet. Eclipse glasses are cheap and much safer. Leave the welding helmet at home and as a bonus you’ll avoid looking like a child pretending to be a robot.
#3 — Put the cameras down
Finally, leave the camera at home too, and put the mobile phone in your pocket. Totality will last for bare minutes and this will seem to pass in the merest blink of an eye.
As totality arrives you will see the pitch black silhouette of the moon where the sun used to be, and surrounding it will appear the faint tendril-like atmosphere of the sun, and a smattering of stars. If you haven’t seen an eclipse before, this is the moment that will change your life. The ephemeral beauty of the sun’s outer atmosphere, which is called the corona, is transcendental. The eerie cold that engulfs you as the sun’s rays are extinguished will literally and metaphorically chill you.
The first two items on my list are mandatory, this third one is optional but I believe it just as strongly. I’ve seen three eclipses, and when the time comes for me to see a fourth, I will go tech-free and just be in that marvellous moment – in the shadow of the moon.
Illustration of a total solar eclipse
Here are some details on how it works:
Each icon shows the view from the centre of its black spot, representing the moon (not to scale) / image by Cmglee / source Wikipedia.org / license CC0
Visualisation of a solar eclipse from different positions. Each icon shows the view from the centre of its black spot, representing the moon.
The diagrams shows the alignment of the Sun, Moon, and Earth during a solar eclipse. The dark gray region between the Moon and Earth is the umbra, where the Sun is completely obscured by the Moon. The small area where the umbra touches Earth's surface is where a total eclipse can be seen. The larger light gray area is the penumbra, in which a partial eclipse can be seen. An observer in the antumbra, the area of shadow beyond the umbra, will see an annular eclipse.
The Moon's orbit around the Earth is inclined at an angle of just over 5 degrees to the plane of the Earth's orbit around the Sun (the ecliptic). Because of this, at the time of a new moon, the Moon will usually pass to the north or south of the Sun. A solar eclipse can occur only when new moon occurs close to one of the points (known as nodes) where the Moon's orbit crosses the ecliptic.
As noted above, the Moon's orbit is also elliptical. The Moon's distance from the Earth can vary by about 6% from its average value. Therefore, the Moon's apparent size varies with its distance from the Earth, and it is this effect that leads to the difference between total and annular eclipses. The distance of the Earth from the Sun also varies during the year, but this is a smaller effect. On average, the Moon appears to be slightly smaller than the Sun as seen from the Earth, so the majority (about 60%) of central eclipses are annular. It is only when the Moon is closer to the Earth than average (near its perigee) that a total eclipse occurs.