Eclipse!!!

In nine weeks, on August 17, 2017, residents of the continental United States will be treated to a total solar eclipse as they enjoy their noon-time repast. If you are standing along the line of totality, which stretches from Oregon’s Pacific coast to South Carolina’s Atlantic surf, and if you have a good telescope, you may even be treated to a view such as the one below photographed by Luc Viatour ( www.Lucnix.be) during the August 1999 total solar eclipse over France!

In this blog, I am going to mention some of the work I am doing to help the public enjoy this once-in-a-lifetime event through my various projects at NASA. NASA, as part of its informal education programs, has adopted this event as a major national PR effort to focus its many assets on the ground and in space. In early-2016, my group at the NASA Goddard Spaceflight Center called the Heliophysics Education Consortium (HEC) was asked to lead the charge organize this event. Led by Dr. Alex Young, the HEC team has created the Official Eclipse website, and I have had the great pleasure and honor to have written many of its resources. So, think of this Blog as an introduction to the What, Where, When and How of this eclipse, and a personal tour by me for how you can enjoy this rare and magnificent event!

First, you probably have a lot of questions about solar eclipses, so I wrote a FAQ Page that covers most of the common ones. I also wrote an essay about the many Eclipse Misconceptions that people have had about solar eclipses. Some are quite bizarre, but seem to be passed on from generation to generation despite our deep scientific understanding of them!

Take a look at the picture at the top of this blog. During most total eclipses of the sun, you are guaranteed to see the brilliant solar corona. With a telescope or a good telephoto lens, you may even glimpse the reddish hue of the solar chromosphere following along the darkened limb of the moon. Here and there, you may even see a solar prominence also glowing in reddish light. These features are hard to see because they are rather small and with the naked eye you just don’t have the natural magnification to see them well.

I will be writing a number of  essays that discuss particular aspects of the sun and post them at the Eclipse SCIENCE page. Topics will include the corona, prominences, chromosphere and the dramatic helmet streamers  so far as astronomers understand them today. It’s all about solar magnetism and how this interacts with the 100,000 degree plasma in the solar atmosphere. The corona, itself, has a temperature of several million degrees! It is about a million times fainter than the disk of the sun, which is why you only get to see it during an eclipse. But astronomers can use instruments called coronagraphs to artificially eclipse the sun, and allow us to study coronal features at our leisure.

There are many things you can do while waiting for the eclipse to start, and a few non-invasive things you can do while the eclipse is in progress. I have tried to collect these ideas into two areas called Citizen Explorers and Citizen Scientists depending on how serious you want to be in exploring eclipses. If you have a mathematical mind, I have even created a dozen or so curious Math Challenges that help you look at many different aspects of the event.

Just about everyone is going to want to use their smartphones to photograph the eclipse, so in my article on Smartphone Photography I try to outline some of the things you can do, what kinds of technology you need like inexpensive telephoto lenses, and what to expect. Below is a photo taken by a smartphone with no other technology from Longyearbyen, Svalbard in 2015. Your camera phone will give you a brilliant, over-exposed corona but don’t expect detailed resolution because your lens is simply not good enough to show details like those in the photo above. If you use an inexpensive smartphone telephoto with 15x or higher, you need a camera tripod too. Also, be careful that you do not use the telephoto on the sun while the brilliant photosphere is visible to avoid camera damage. (Credit: Stan Honda/AFP/Getty Images)

Some people may be interested in uploading their images, and in my essay on Geotagging I describe two ways that you can upload your selfies so that others can enjoy your efforts. The first is to use GOOGLE Maps but you can only upload your photo to  preexisting ‘tagged’ locations in GOOGLE Maps (nearby businesses, monuments, parks, etc). This is unlike the discontinued Panoramio/GOOGLE Earth feature where you could upload your picture to any geographic location on the planet. The second way is to send your pictures to a NASA site that is collecting them.

For a rare event like this, you might also want to create a time capsule of your experience. I have suggested that you write a letter to yourself about who you are today, and what you think the future holds for you. On April 8, 2024 there will be another total solar eclipse across the continental United States and you might set that date as the time when you next read your letter being at that time 7 years older!

People have observed total solar eclipses for centuries, and in my Eclipse History area I have a number of essays that describe earlier observations in the United States. There is even an archive of newspaper articles since the early 1800s in which you can read  first-hand accounts. Some music has also been written and performed with solar eclipses in mind! In my Music Page I list many of these pieces both in classical and pop music over the years. Who can forget Carly Simon’s ‘…You flew your Lear Jet to Nova Scotia to see the total eclipse of the sun’ about the March 7, 1970 eclipse!

One thing I find interesting is that since the 1500s there have been over a dozen eclipse paths that have crossed the one for August 21, 2017. I created several resources that describe these ‘magical’ crossing points and what history was going on in North America during these dates. I also created a set of math problems where you can calculate the latitude and longitude for these crossing points  if you are in-to math!

Where should you go to see this eclipse? In one essay I discussed how  there are dozens of airline flights on that day from which passengers may be able to see the total solar eclipse out their windows if the Captain gets you to the right place and time along the route. For folks on the ground, you can check out NASA’s Path of Totality maps and see if your travels on that day take you anywhere close. For the rest of us, no matter where you are in North America, you will at least see a partial solar eclipse where a small ‘bite’ is taken out of the solar disk. With a pair of welder’s goggles or solar viewing glasses, you can look up anytime around noon and see the eclipse in progress.

Created with GIMP

NASA plans to collect stunning images from some of its available spacecraft, so on this page I collected information about which spacecraft will participate. After the eclipse, you will see in the News Media many of these images as they are produced during the days after the event.

Myself, I will be joining the NASA Eclipse Team in Carbondale, Illinois for a huge public celebration of the total solar eclipse. This will be televised through numerous NASA feeds all along the path of the eclipse so you can view it on your smartphone or laptop screen wherever you are. I will be involved with this telecast between 11:45 and 1:45 CDT as a panelist on several of the program segments. When I return from this event, or perhaps even during it, I will upload a follow-up blog about what it was like from ‘Ground Zero’. I have never experienced a total solar eclipse before, so I am prepared to be stunned and amazed!

Stay tuned!

Exoplanets Galore!

***This Blog was updated in 2023 with new data. Visit Exoplanet Update. 

The year was 2001 – The first of the new millennium. It was also the year astronomers reached a historic milestone: They had catalogued more planets orbiting distant stars than the eight we knew about in our own solar system!

The first of these was discovered in 1988: A Jupiter-sized world orbiting the star Gamma Cephi A at a distance of 45 light years from our sun. Since then, well over 3,600 ‘exo’planets have been discovered using many different detection methods both on the ground and in space. We are truly living in a very different age than we experienced only a few short decades ago. We no longer have to speculate whether other planetary systems exist across the universe. We now have the technology and a growing catalog of examples to prove our solar system is not alone in the universe!

One of these detection methods is the Transit Method. As a planet passes in front of its star as viewed from Earth, the brightness of the star dims by an amount equal to the ratio of the planet’s circular area to the star’s circular area. For example, a Jupiter-sized planet has a diameter of 143,000 km while a sun-like star has a diameter of 1.4 million km, so the ratio of their areas is 1/100. As this exoplanet transits the disk of its star as viewed from Earth, the brightness of the star will dim by 1%. By measuring the time between successive transit ‘dips’ you can deduce the orbit period of the planet. From the orbit period and the mass of the star you also obtain the distance between the star and the planet. Once you have this information, you can estimate the surface temperature of the planet and its average density (rocky planet or gas giant). In the example below, the orbit period is 4.887 days and from the amount of dimming ( 0.7%) the ratio of their areas is 1/142, and planet’s diameter is 1/12 the diameter of its star.

To take advantage of the transit method on a large scale, NASA launched the Kepler Observatory in 2009. Using a super-sensitive digital camera, it took a picture of the same star field in the constellation Cygnus every minute and captured brightness information for over 150,000 stars similar to our sun. Over the course of its survey, now in its eighth year, it has discovered 4,496 exoplanet candidates of which 2,335 have been verified by independent study. These statistics now show that virtually all stars in the sky have at least one planet in orbit around them, and about 1 in 20 have Earth-sized worlds!

What was entirely unexpected was the diversity of exoplanet types, and orbits about their parent stars. Our solar system offered as templates the small rocky Earth-sized worlds of the inner solar system, the two gas giants (Jupiter and Saturn) and the two ice giants (Uranus and Neptune), but among the thousands of worlds discovered so far, a vaster array of possibilities have been found.

There are super-Earths over three times as large as our world apparently fully covered by deep oceans (Kepler 22b). There are hot-Jupiters that orbit their stars in a matter of hours, and swelter at temperatures of thousands of degrees (51 Pegasi b). Some planets have ‘water cycles’ in which silicate rock evaporates from their surfaces, condenses in clouds, and then rains droplets of lava back to the surface (COROT-7b, Alpha Centauri Bb, Kepler 10b). The cloud-shrouded super-Earth GJ 1214b is so hot that its clouds could be made of zinc sulfide and potassium chloride! One exoplanet is so close to its star that it is literally evaporating before our eyes, leaving a huge comet-like tail of gas in its orbital wake (HD 221458b).

The thousands of exoplanets detected by the transit method are especially intriguing. From Earth, as the exoplanet passes in front of its star, some of the starlight passes through the exoplanet’s atmosphere. Various gases in the atmosphere absorb selected wavelengths of this light and leave their unique fingerprints behind for distant astronomers using spectroscopes to study. So far among the dozen or so worlds examined, atmospheres rich in water vapor, carbon dioxide, methane, sulfur and other common molecules have already been found. This figure shows the spectrum of the exoplanet Wasp-19b and signs of methane (CH4) and hydrogen cyanide (HCN) – a lethal mixture for humans to breathe! Future ground and space-based observatories will be able to detect the molecules in thousands of exoplanet atmospheres, but this is no idle scientific pursuit. Living systems on a planetary scale sculpt their atmospheres by creating free molecular oxygen, so if we ever detect an exoplanet atmosphere rich in oxygen, it will be a major discovery of life in the cosmos beyond our own Earth.

Another aspect of the search for Earth-like worlds is to find exoplanets about as large as Earth that orbit their stars in what is called the Habitable Zone (HZ). In this range of orbital distances from the exoplanet’s star, the surface temperatures would allow liquid water to exist. In our solar system, this zone is located between the orbits of Venus and Mars, and Earth is smack in the middle of it. Currently, the various surveys have identified 13 exoplanets that are not only Earth-sized but are within their star’s HZ. The closest of these is GJ 273b at a distance of 12 light years! But there are complicating factors to finding an exact twin to our Earth upon which we might also hope to discover a living biosphere.

If a planet in the HZ has too much carbon dioxide – a potent greenhouse gas – its temperature would be more Venus-like and it would be a desert world or worse. If the exoplanet had significant traces of common gases such as hydrogen cyanide or methane, it would be unbreathable for humans though some extremophile bacteria on Earth thrive in such environments.

Another thing to think about is that an Earth-like world could be in orbit around a Jupiter-sized exoplanet in its star’s HZ. Even though we do not directly see the Earth-sized world there could be several of them as satellite worlds of larger exoplanets. The Jupiter-sized exoplanet WASP-12b appears to have an ‘exomoon’ with several times the mass of Earth. We know of hundreds of Jupiter-sized exoplanets orbiting in the habitable zones of their stars. We can no longer discount the possibility that their exomoons may be Earth-like though currently undetectable.

So far we have had to detect and study exoplanets indirectly from transit and spectroscopic data, but in a growing number of cases we can actually directly see these worlds as they spin around their stars. In 2008, the bright star Fomalhaut was observed by the Hubble Space Telescope and revealed a small planet among the debris of its dense disk of gas and dust. In another instance, the young star HR 8799 was observed by the Keck Observatory in Hawaii and revealed four massive planets (HR8799 b, c, d and e) in orbit. This is only the beginning of direct-imaging studies as we enter a new era of exoplanet studies.

What will the future bring? The spectacular success of the NASA Kepler mission is just the beginning of new missions to come that will discover thousands of new exoplanets. The NASA, Transiting Exoplanet Survey Satellite (TESS) will be launched in 2018 and will perform a Kepler-like survey of the 500,000 brightest stars in the sky. This survey will double the number of known exoplanets and include hundreds of additional Earth-sized candidates. At the same time, the Webb Space Telescope will be launched and among its many research programs will be ones to study the atmospheres of known exoplanets and Earth-sized candidates.

Check back here on June 18 for my next blog!