Chasing the shadow: A 2017 eclipse adventure

Article written by: Conor Byrne


As an astrophysicist with a keen interest in space from a young age, the opportunity to witness a rare astronomical phenomenon is naturally quite high on the ‘bucket list’. So when I was attending a research workshop in the United States in August 2017, just a few days before a solar eclipse passed through, I wasn’t going to let this opportunity pass me by! By the end of this article, I hope I’ll have convinced some of you that it’s worth trying to see a total eclipse at least once in your life if you haven’t already!

Eclipses have been observed for thousands of years and played a big role in influencing mythology around the world, such as the Chinese stories of the dragon that ate the Sun. A solar eclipse is an extraordinary event where the Moon passes directly between the Sun and the Earth, casting a shadow on the surface of the Earth. The Moon passes between the Earth and the Sun once a month, and this is why we get New Moons, as the Moon is in the same part of sky as the Sun, and we see no light being reflected off its surface. This might lead you to think that a New Moon will always result in a solar eclipse, however this is not the case.

The Moon orbits the Earth at an angle relative to the Earth’s orbit around the Sun. This means that in most months, the Moon is either higher or lower in the sky than the Sun when it reaches its New Moon phase. However, if the Moon is passing through the plane of the Solar System at the time of a New Moon, then the Sun, Moon and Earth lie in a straight line and a solar eclipse occurs.

Fig 1: Diagram illustrating the different shadows (umbra and penumbra) that the Moon casts on the Earth during an eclipse. The very small region within the umbra is where a total eclipse can be seen. (Credit: NASA)

 

The Moon happens to be about 400 times smaller than the Sun, but also 400 times closer, meaning that it’s just big enough to totally block out the Sun. This means that a total eclipse is generally only visible over a narrow area, while a much larger area of the Earth witnesses a partial eclipse. In the case of the 2017 eclipse, the path of totality (the region where the Sun gets fully obscured) passed across the US, while most of North America was treated to a partial eclipse. In fact, a barely noticeable 3% partial eclipse was visible from Armagh just before sunset on the day.

Fig 2: Path of the 2017 eclipse. The total eclipse started in Oregon in the northwest and moved across parts of 14 different states, ending in South Carolina about 90 minutes later. The partial eclipse was seen all across North America. (Credit: AAS)

 

Organising an eclipse viewing trip proved a tricky task. A former research student at the Observatory also expressed interest in viewing the eclipse so we put our brains together to come up with a plan. A lot of factors needed to be considered, first and foremost the places most likely to have good weather on the day. The last thing we wanted was clouds obscuring the view! Oregon and Idaho, west of the Rocky Mountains, had some of the driest weather for August, so this became our target area. However, this added its own complications. This part of the US is quite sparsely populated and accommodation options were few and expensive. Some hotels on or near the path of totality had apparently been booked out 12 months in advance! Eventually we found a reasonably priced hotel about a 90 minute drive from the eclipse path. This left us with a 4 and a half hour journey from the nearest major airport in Salt Lake City. And so our great American road trip began. I could write an entirely separate blog article on the trip, but I should probably stick to the astronomy!

We eagerly watched the weather forecast the night before the eclipse. Everything was looking good. We surveyed our maps and decided to aim for the city of Rexburg, Idaho. This city of 25,000 people would, for about 2 and half minutes, be the site of the most remarkable sight on Earth. We arrived in plenty of time to pick a good vantage point and were welcomed by clear blue skies. Now, all we had to do was wait for the Moon to get into position. The local radio station was, of course, playing ‘Total Eclipse of the Heart’ by Bonnie Tyler for the occasion!

Fig 3: Various stages of the solar eclipse as the Moon obscures progressively more of the Sun. (Credit: Conor Byrne)

 

There are a lot of environmental changes can be observed during a solar eclipse. The most apparent one is that it starts to get darker. This confuses both animals and machines. The birds stopped singing, thinking that night was falling, while the street lighting thought likewise!

Fig 4: Compare these two images from the same location. The one on the left was taken at 10:30 am around the start of the eclipse, the other taken moments before totality. The amount of light being obscured by the Moon gives a distinct twilight feel even though it is the middle of the day. (Credit: Conor Byrne)

 

But another thing you notice as the eclipse progresses is that the temperature begins to drop. Without the energy from our nearest star shining down on us, the air begins to cool. The crowds fell silent as the anticipation built up. What followed was a moment of pure magic.

Fig 5: The moment everyone had been waiting for, the total solar eclipse! If there was a point in my life where I wished I had invested more in camera equipment, this was it! Looks incredible nonetheless. (Credit: Conor Byrne)

We stood in awe as the Sun was fully obscured, revealing the glow of the solar corona (the hot, faint material that stretches millions of kilometres from the Sun’s surface). I found the experience quite emotional. Months of planning, thousands of miles travelled and perfect weather conditions had all come together for these 2 minutes and 20 seconds. I was lucky enough to see some of the 2015 partial solar eclipse through the clouds in Dublin, but it was totally eclipsed by what I saw on the 21 August 2017.

Here are some top tips and information on observing a total solar eclipse:

  • Don’t look at the Sun!  This one goes without saying really, only look at the Sun if you’re using special eclipse glasses that have strong filters to block out almost all the light from the Sun. Once the Sun is totally eclipsed, it is safe to take off your glasses, but be ready to put your glasses on before the Sun starts to reappear. Alternatively, you can make a pinhole camera and use this to look at a projection of the Sun’s image onto a piece of paper.
  • Plan well in advance: Hotels in/near the path of totality will be booked out well in advance, so one idea would be to look for a major city on the path as they will have more accommodation options.
  • Have a ‘Plan B’: Depending on the location, it may be important to consider the weather. It helps to have flexible plans/a backup observing site in case it is cloudy.

 

OK, I’m interested, when/where can I see one?

  • The next total solar eclipse is on 2nd July 2019 and will be visible from parts of Chile and Argentina.
  • The next total solar eclipse visible from Europe is on 12 August 2026 and will be seen in northern Spain. A 94% partial eclipse will be visible in Armagh.
  • If you want to wait to see one in the UK or Ireland, you’ll have to wait until 23 September 2090 (totality in West Cork and Cornwall).
  • On 14 April 2200, Armagh will be the centre of attention as the path of totality will pass right over us!