ST
Solar-Terrestrial Sciences

Solar-Terrestrial Sciences

The 2017 solar eclipse and scientific discoveries

The 2017 solar eclipse and scientific discoveries

The next solar eclipse is upon us. On August 21 the moon will pass between the Sun and an observer’s point of view in America and block out daylight, creating an eerie gloom in the sky. The transit of the moon between the Earth and Sun occurs about every 18 months, but for your particular city it can take several hundreds of years before a new eclipse occurs. The figure below shows the paths of all solar eclipses that occurred or will occur during the 2001 to 2020 period. Few eclipses happen around the North or South pole due to the orbital geometry of the heavenly bodies, so proportionally the odds are higher to experience midday darkness if you live at low or mid latitudes. However, since about 71% of the Earth’s surface is covered with water, most of these eclipses occur at places where no one lives and go by unnoticed. Unless you travel to them!

People have long been fascinated by solar eclipses and records in history have been found as early as 2000 B.C. Throughout history researchers and science enthousiasts have travelled the world to watch eclipses, endeavours which were much more difficult in the early days than with nowadays commercial flights. Maybe you are travelling as well to watch this eclipse.

Paths of total and annular solar eclipses during the 2001-2020 period. Credit: Fred Espenak, NASA/GSFC Emeritus

By studying the sun and the eclipses, scientists can look at features of the solar atmosphere that are otherwise hard to observe from the ground due to the intense brightness of the Sun. Discoveries made during eclipses include observations of the outer parts of the solar atmosphere (solar corona), flames of fire from the sun (prominences, jets), radiation other than visible light (infrared, UV) and otherwise invisible comets travelling around the Sun. During the 1868 eclipse a yellow spectral line was discovered by J. Lockyer in the solar chromosphere from a yet unknown chemical element that turned out to be one of the most abundant chemical species in our universe. He named it after the Greek word for the sun (helios) and it took until 1895 before helium was discovered on Earth.

Even today, scientific knowledge is being advanced by studying the solar eclipse and the effects on our nearby space environment and Earth’s atmosphere. When the moon eclipses the Sun, the illumination over a localised region will change rapidly and Earth’s atmosphere will react to this decrease in solar energy. One such reaction that occurs is in the ionosphere, the higher most reaches of the atmosphere. Solar ultraviolet radiation creates a dynamic layer of charged particles that reflect telecommunication transmissions at very low frequencies around the world. Understanding how this layer reacts to changes in solar radiation can enhance our understanding of the ionosphere and hopefully improve the region’s dynamics in model simulations. The direct blocking of radiation will also have a profound effect on the total amount of radiation that is received by the surface as well on the amount that is reflected back to space by the oceans, clouds and atmosphere. Changes in this radiation budget can in a unique way be investigated during the solar eclipse. Studying these variations, in for example temperature or radiation, during an eclipse are useful to test our current understanding of the Sun’s effect on the atmosphere.

Not only academics, but also citizens can contribute to advances in solar-terrestrial science. The Megamovie project aims to create an open-source archive of nearly 1.5 hours continuous solar eclipse. With this dataset new features in the solar corona on long and short time scales will hopefully be discovered.

So, what will you do on 21 August 2017? Watching the eclipse from your hometown, travelling to the path of totality from across the world or take part in any scientific contribution as citizen or researcher? Hopefully you will enjoy the magical moment and experience something new!

For more information: 

http://www.mreclipse.com/Totality2/TotalityApH.html

https://eclipse2017.nasa.gov/science-ground

https://eclipse.gsfc.nasa.gov/solar.html

Capturing a Whole Total Eclipse of the Sun: Megamovie

Capturing a Whole Total Eclipse of the Sun: Megamovie

by Hugh S Hudson (U. of Glasgow and UC Berkeley)

Normally solar eclipses give an observer only a fleeting moment (minutes at most) to enjoy the solar corona. We aim to amplify that considerably in the August 21 eclipse across North America. The plan is simple: Megamovie will capture everybody’s images, especially those from a group of 1,000 photographc volunteers, and compile them into an open-source archive that (weather permitting) will span an hour and a half of the corona’s life. One can find this program at the URL “eclipsemega.movie“, and in the  smartphone app “Eclipse Megamovie Mobile“.

The path of totality crosses the entire continent of North America, well-populated with eager observers equipped with the latest things in consumer electronics – marvelous cameras plus GPS and the Internet. The previous occurrence, in 1918, had none of that.  The program is thus a citizen-science project, embracing all levels of experience and capability among the observers, and at the same time it will produce a systematic record that we believe will be the first of its kind, and certainly can be the largest. We intend to follow up with citizen-science analysis projects, along the lines of SETI@Home and Zooniverse, to make sense of the very complicated records.

Megamovie does new and original things that will create real science. For the corona, the existence of the archive itself is unique.  Here we will have vast oversampling in the time domain, with access to disturbance modes on short time scales seldom observed with such resolution. Here we expect to see waves and flows in the low corona, by following the intensity variations of discrete features. Of course the Megamovie archive can extend to time scales of tens of minutes, where we know that large-scale structures will show perceptible and dynamically interesting motions. How much does a streamer wobble, and in what mode?

A CME and other structures captured in eclipse observations by Hanaoka et al. (2013); the left panel is an edge-enhanced view of one stacked image at 12-Nov-2012 20:39 UT. The right panel is a difference against observations from a different site at 21:14 (this is a cropped version of Figure 1 of the manuscript used by permission from Dr Y. Hanaoka)

The uniqueness of the August 21 eclipse continues with the coincidental presence of the bright star Regulus. This reference point will show up in all of the deep coronal images. In addition we have recently achieved precise astrometric information about the Moon, derived from the Kaguya and Lunar Reconaissance Orbiter missions; this eclipse will be the first major opportunity to apply this new information to eclipse data and the Sun.

The star field at the time of the August 21, 2017 eclipse,showing the position of the Sun as it moves during totality, and also the nearby bright star Regulus. (Figure provided by H. Hudson)

These advantages should make it possible to analyze and correct many images at a precision  rivaling that of the famous Eddington observations in 1919. We note that this historically important confirmation of general relativity has been repeated with modern detectors such as those found in everyday consumer electronics now. The Megamovie Mobile app (free) provides many resources for smartphone users; the mere timing of Baily’s Beads will make a systematic recording of the shadow path and thereby the local instantaneous radius of the Sun. The app does this automatically, and even without a cheap telephoto attachment, a smartphone camera can get wonderful timing information with precise GPS metadata.

Welcome

Welcome to the ST division blog!

The Solar-Terrestrial (ST) Division of European Geosciences Union (EGU) is starting its own blog! The blog is an initiative by a group of enthusiasts who met during the EGU’s General Assembly in April 2017. We are thrilled to set up this blog that will keep our readers informed about a range of topics relevant to the science of the division.

A CME from the Sun heading towards the Earth. Thanks to the magnetic field enveloping the Earth, we stay protected from the wrath of the Sun.
Credit: Adapted from NASA/Steele Hill

The influence of the Sun on the Earth and our planetary system have shaped a dynamic, constantly evolving scientific area. The Earth’s atmosphere, ionosphere and magnetosphere are strongly moulded by the Sun, solar wind and galactic cosmic rays. We have an armada of spacecrafts and detectors on the ground to record solar eruptive events and their in-situ manifestations. This helps us study the ST sciences.

The Sun fosters life on Earth and acts as the vitalizer of our very existence. However, it spews large amounts of plasma and energy towards the Earth that can hinder day-to-day life in modern society.

Space weather and terrestrial weather are continually influenced by small changes in solar output, which not only varies from day to day but also through longer timescales throughout its lifetime. Studying the Sun and its effects on the near-Earth environment can facilitate more accurate predictions of space and terrestrial weather. Such forecasting can in turn help keep life on this planet safe by having early warning systems.

Research in the ST sciences is very stimulating for us and we wish to share our enthusiasm with our readers. Bringing science to the public is the intent of this blog. Students as well as early career scientists (ECS) will greatly benefit from the broad nature of topics that will be discussed here. Getting everyone excited about science in general and ST studies in particular is our aim. We will discuss papers in the “spotlight” to look at the recent breakthroughs in this field. There will be articles and interviews of featured scientists to discuss post-doc life, career path or alternative careers.

As well as  exciting scientific topics we will also provide informative general highlights and timely deadlines for conferences. From time-to-time our own EGU-ST ECS representative (Jone Reistad) will discuss ECS related opportunities and problems. All in all, this will be a voice for scientists to reach out to the community.

We have planned an extensive series of blogs from our team of experts and other scientists (especially ECSs and students). We encourage guest bloggers to contact the editor. Come back every month for a new and informative blog post.

 

This text was prepared by Kamalam Vanninathan and Athanasios Papaioannou

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