The total solar eclipse taking place this coming April 8th already deserves the title of “The Great Solar Eclipse of 2024.” With 30 million people living on or visiting its “path of totality” (crossing land from Northern Mexico, the US from Texas to Maine, to part of Eastern Canada), and being from there broadcasted to the whole World, it promises to become one the best ever observed and enjoyed solar eclipses.
Solar total eclipses have always been intense and deeply moving events. Since prehistoric times they have been associated with our deepest existential fears, understood as the fierce battle between powerful gods and as urgent motifs for praying, or taken as exceptional opportunities for the advancement of science.
Free from a few fantasized threats and mystical interpretations, we can nowadays perceive total solar eclipses as breathtakingly beautiful astronomical events. Outstanding confirmation of the physical laws at a rather large scale, they offer us the opportunity to look at things from a wide perspective. In the cosmic dance which our planet humbly participates in while carrying all its fragile life across space, the Moon and the Sun gift us with their best pas de deux. ...A total solar eclipse has the power to remain in our minds as one of our most cherished memories.
Figure 1: Totality path of the solar eclipse of April 8th, 2024. You must be somewhere on this "path of totality" if you want to have any chance of observing the solar corona. Outside of it and up to a certain distance the eclipse can be observed only as partial. The closer to the totality path the larger the percentage of the solar disc that becomes covered by the Moon. As a reference, time marks are shown for particular locations. [Image credit: NASA]
It has started! …The mere confirmation that a solar eclipse begins precisely the way it had been predicted for years is already a cause for astonishment. At present, eclipses can be predicted centuries in advance with an error of less than a minute. With to-the-second precision, a tiny black mark appears at the indicated point on the contour of the solar disc. Advancing in the expected direction and with the calculated speed as a larger and larger curved shape, the Moon relentlessly eats up the bright disc of the Sun.
Solar Eclipse August 21, 2017. Video credts: Axel Mellinger.
Despite the Sun still being above the horizon, at some point, its reduced luminosity becomes evident. As temperature plunges and winds start to change, a surreal kind of crepuscular light announces an anachronic night is about to start. ...Even Nature takes notice of it - while some animals prepare to go to sleep early, others choose to start a new hunting campaign or a mating spree.
The best is still to come, for once the solar disc becomes completely covered by the Moon the most spectacular view will unfold before our eyes: the solar corona. Invisible on any common day (and even if during the eclipse we were out of the so called “path of totality”), this faintly bright, whitish, elusive part of the Sun will seem to have been suddenly turned on against a sky that has become dark and starry in day hour. Extending as a majestic presence far out from a now completely round, coal black, lunar disc, the corona will mark the position of the Sun on its constellation - Pisces this time. A rare and awe-inspiring view (Fig. 2).
Figure 2: The solar corona showing some fine details. Image details: 10 frames was combined - most of them are at low exposures; taken with canon 70d + canon 400mm f/5.6; ISO = 1600 (unnecessary high, could be just 200 or so); Shutter speed = from 1/8000 to 1/500; Aperture = f/5.6. [Image credit: Prof. Roman Senkov]
In fact, the beginning of the “totality phase” (the brief moment during which the solar disc remains fully covered by the lunar disc) would have been announced by a short but impressive barrage of events. ...Filtering in between the mountains present on the Moon contour, the last rays coming to our eyes from the almost extinguished solar disc, would have suggested a delicate set of “beads”, perhaps a fulgurant “diamond” against an already darkened sky (Fig. 3). These ephemeral jewels are always better captured with the aid of a safe telescope equipped with an appropriate filter, or through a good photographic lens (Fig. 4). Millions of people (perhaps including yourself) will be well prepared for this on April 8th, 2024.
Figure 3: The red chromosome showing some of its prominences. [Image credit: Prof. Roman Senkov]
Figure 4: Prof. Roman Senkov and his son Sasha using a telescope to capture the eclipse. Before and after the totality phase, a very reflective filter set at the entrance of the telescope allows only for a small amount of light coming from the extremely bright solar photosphere to enter the telescope. During totality the filter is removed in order to capture the dim solar corona. [Image credit: Prof. Roman Senkov]
As the irregular contour of the Moon advanced against (and in front of) the last remaining arch of solar disc visible a brief stream of “flying shadows” had swept our spot on Earth at vertiginous speed, right before the lunar umbra started fully covering it - enigmatic shadowplay cast across hundreds of thousands of miles in the cosmic theater.
Apart from the corona, another usually invisible part of the Sun can be observed during the totality phase: the "chromosphere" ("color" sphere). Usually observed as a bristling reddish circumference right in between the contour of the black lunar disc and the base of the whitish corona, the chromosphere produces a remarkable contrast (Fig. 3).
In the same way this happens with the photosphere (the yellowish "surface" of the Sun that we see as a disc on the sky), neither the chromosphere nor the corona are completely uniform layers. Granulation and sunspots on the photosphere, filaments and prominences on the chromosphere, active regions, streamers, and coronal holes on the corona - all are part of the jargon of the professional as well as the amateur astronomer focused on the Sun. Total solar eclipses offer a unique opportunity for the scientific study of both, the solar chromosphere and the solar corona, or just to motivate oneself to to learn more about the fascinating processes behind their features!
Brief and sweet, the totality phase leaves us longing for more (...perhaps already awaiting the next total solar eclipse!). After only a few minutes (between 3 and 4 minutes in the case of the coming event depending on the precise location), the majestic corona disappears, as a first flash of light emerges from behind the lagging side of the Moon, initiating a sequence of steps that roughly mirror those at the beginning. Gradually retiring from the scene, the Moon allows for the Sun to finally recover its most common role: dominant star of the sky and ultimate support of Life on Earth.
Basic Idea
The basic idea behind eclipses is nowadays common knowledge. A solar eclipse occurs because the Moon - while moving along its orbit - briefly crosses in front of the Sun, at least as seen from some favored but very restricted region on our planet (the “totality path”). On the other hand, a lunar eclipse can be observed each time - according to the same motion - the Moon enters the shadow cone that Earth casts into space …and can be then observed by anybody having the Moon above the horizon at that moment.
Figure 5: Umbra and penumbra cast by the Moon on the surface of the Earth. Observers inside the umbra will see a total solar eclipse; standing inside the penumbra, though, the eclipse will be seen only as partial. [Image credit: Glen Williams]
Figure 6: As the Moon moves in its orbit around the Earth and the Earth rotates around its own axis, umbra and penumbra sweep the surface of the Earth, defining the path of the eclipse. [Image credit: Glen Williams]
But, exactly how do any of these astronomical events happen? Why is it that they seem - at least at first sight - so capricious in terms of their occurrence in comparison to seasons and lunar phases (highly regular phenomena to which human activities have adjusted for thousands of years and to which eclipses are directly related)?
Good Partners
We should begin by emphasizing how crucial, as well as fortunate, it is that the sizes of the Moon and Sun, and their distances relative to Earth, are what they are. This is precisely what is behind the fact that, when we observe the Moon and the Sun from Earth, they both present very similar "apparent sizes" (or angular sizes): approximately ½ degree (or 30 arc minutes).
As we know, though the Sun is much larger than the Moon, its distance from the Earth is also a lot farther than that of our satellite. With 1,400,000 km in diameter (compared to 3,500 km in the case of the Moon) but being located 150,000,000 km away from Earth (compared, roughly, 380,000 km for the Moon–Earth distance), the disc of the Sun is susceptible of being covered by the disc of the Moon given the opportunity ...and this superposition is “almost perfect”:
\begin{equation} \mbox{Sun: } \theta_{Sun} = \frac{1,400,000\,km}{150,000,000\,km} \approx 0.00933\,rad = 0.535\,deg. \end{equation} \begin{equation} \mbox{Moon: } \theta_{Moon} = \frac{3,500\,km}{380,000\,km} \approx 0.00921\,rad = 0.528\,deg. \end{equation}In reality, due to the eccentricity of the Moon and Earth orbits, the “angular sizes” of the Moon and the Sun vary a bit around this approximate value of ½ degree. If, for example, a solar eclipse occurs when the Earth is closer to the Sun and the Moon somewhat farther from Earth in its orbit, the moon will not be able to completely cover our star and the eclipse will be “annular”: a bright solar disc with a smaller dark lunar disc more less at its center. Annular solar eclipses are to some point also aesthetically pleasant (even if the chromosphere or corona cannot be then observed) but certainly have for this reason not as much scientific value.
In contrast, if the eclipse occurs when the Earth is somewhat farther away from the Sun than average and the moon is rather closer to Earth, then the moon will be able to cover the Sun in excess - although not much in excess, which is good, because we don’t want for the Moon to cover the chromosphere or an important part of the corona! We want it to cover “just” the bright yellowish disc of the Sun (the “photosphere”, as we see it from Earth). This is precisely the case for the eclipse occurring on April 8th, 2024.
Figure 7: Angular sizes of the Moon and Sun depending on their distance to Earth. [Image credit: Glen Williams]
We have just identified one of the reasons for the "capriciousness" of solar eclipses: the slight variation of lunar and solar apparent diameters around an average of approximately 1/2 degree, according to the variation of their distances from Earth. A few other factors make things even more complicated.
A Matter of Pace
Solar and lunar eclipses require a "good enough" alignment of -respectively- the triad Sun-Moon-Earth or Sun-Earth-Moon, in order for the shadow of the Moon to be cast on Earth or that of Earth to be cast on the Moon. These are -basically- two particular configurations among the infinite but somewhat repetitive configurations these three bodies acquire as the Moon and Earth move along their orbits.
We can imagine -at least in principle- that it is precisely the repeated succession of lunar phases (New Moon, Waxing Crescent, First Quarter, Waxing Gibbous, Full Moon, Waning Gibbous, Third Quarter, Waning Crescent, and all over again), which are produced by the combination of -both- Moon’s and Earth’s orbital motions, that set the pace of solar and lunar eclipses. Without going into much detail, we can recall that the cycle of lunar phases has a period of 29.5 days.
Do we have a solar and a lunar eclipse each and every month?
Not So Easy
Based only on our experience as persons able to marvel at the observation of the rising Full Moon, we might remember that such a thing always happens when, at the same time, the Sun is setting. When we look at the rising Moon, the Sunset in happening at our back. …But, if we are standing on Earth, is this not the case of a Sun-Earth-Moon configuration required for a total lunar eclipse to happen? One thing is clear: if we are looking at the Full Moon, fully illuminated, then we are not experiencing a lunar eclipse.
The explanation to these puzzling questions lie in criticism of those overly simplified drawings of the Earth and the Moon in their orbits we often find in books. If the orbits of the Earth and Moon rested on the same plane (as they are frequently represented without further clarification), then, for each lunar cycle, two moments of perfect alignment would take place: one of the form Sun-Earth-Moon, the other of the form Sun-Moon-Earth. If that were the case, a lunar eclipse would take place every Full Moon and a solar eclipse every New Moon. Remember: we know from our experience that this is not the case.
Figure 8 shows, instead, a more realistic representation of the situation. The plane of the Moon’s orbit around Earth in fact forms an angle with the plane of Earth's orbit around the Sun - a 5 degree angle, approximately (which is almost 10 times greater than the angular size of the Moon!).
The consequence is that, even if a “configuration” Sun-Earth-Moon or Sun-Moon-Earth occurs on each lunar cycle, that doesn’t necessarily mean that precise alignment, or even a “good enough” alignment of these three bodies is obtained. Most times the Shadow of the Moon will miss the Earth (“frustrating” the possibility of a expected solar eclipse “expected” to occur on a New Moon), while in other occasions the shadow of Earth will not cover the Moon (“frustrating” the possibility of a lunar eclipse expected to occur on a Full Moon).
Only when a New Moon or Full moon occurs at the same time when the Moon is on the plane of Earth’s orbit, or close enough to it, does a solar or a lunar eclipse take place -respectively.
Figure 8: The orbits of the Earth around the Sun and of the Moon around the Earth do not rest on the same plane but, in fact, form a 5 degree angle. For that reason, a solar and a lunar eclipse do not take place each lunar month, as we might otherwise expect to happen, respectively, on each and every New Moon and Full Moon. Because of the angle formed between the orbital planes, most times these lunar phases occur, the shadow of the Moon misses the Earth, and that of the Earth misses the Moon. A necessary condition for a solar or lunar eclipse to effectively happen is for the Moon to be close to the plane of Earth orbit when New Moon or Full Moon are -respectively- taking place (see “Eclipse season” in the picture). When that happens it is not rare to witness a lunar and a solar eclipse (or vice versa) separated by just a couple of weeks (time between two consecutive Full Moon and New Moon Phases). The lunar and Solar eclipses of March 25th and April 8th, 2024 are an example of this. [Credit: Wikimedia Commons]
Figure 1 shows a part of the "path of totality" of the April 8th, 2024 total solar eclipse. In general, the totality path of a solar eclipse is -as we would expect- the only place from which the totality phase can be observed, but the moment at which it can be observed depends on the precise location of the observer.
The width of this path is usually around 160 kilometers (100 miles) and the more or less elliptical shadow of the Moon moves along it at a speed of some 2000 miles per hour. This is more than [twice] as fast as the cruise speed of a commercial plane!
Though it might be already clear, it is important to emphasize the following: If you are located outside this path, even if you miss it by a few meters, you will not see the totality phase. You might still see a Sun that is 99,9% covered by the Moon, but you have to remember that the smallest bit of solar disc that remained visible would completely ruin the possibility of observing the Solar Corona (so bright is the "surface" of the Sun and so dim the Corona, indeed!).
The farther away you are from the totality path, the smaller fraction of the solar disc you will see covered by the Moon during the eclipse. The way astronomers express this is by means of the so-called "magnitude of the eclipse", which is defined as just the maximum fraction of the Sun's apparent diameter that becomes covered by the disc of the Moon during the eclipse. If you are unlucky enough to find yourself off the totality path at the moment of the eclipse, you might want to know at least how good a partial eclipse would be for your location. You can see this by looking at the iso-magnitude lines on Fig. 1.
Beyond a certain distance from the edge of the totality path (on each side of it), the eclipse will not be noticeable at all, and you will see the Sun as in any normal day, without noticing that the Moon is -though invisible to your eyes- very very close to it on the sky.
Location and Time: For an optimal viewing experience of the partial solar eclipse in New York City, select a location with a clear and unobstructed view of the sky. Public parks such as Central Park or the Brooklyn Heights Promenade offer expansive views, making them ideal choices. Ensure you're set up at least 30 minutes before the eclipse begins to fully experience the event. Check local astronomical societies or event listings for any organized viewing parties, which can offer additional insights and a communal atmosphere. If you're aiming to witness the total solar eclipse, consider planning a trip to the nearest locations in New York State within the path of totality. Areas on the edge of the path can still provide a remarkable view, so you don't need to aim for the exact center. However, these events attract large crowds, so it's wise to book accommodations well in advance. Look for hotels or campsites in the towns along the path of totality. Remember, early planning is key, as availability decreases closer to the eclipse date.
Observation: For a safe and memorable solar eclipse viewing experience, it's crucial to prioritize eye safety. Directly observing the sun without proper protection can cause serious eye damage. The only exception is during the brief phase of "totality," when the moon fully covers the sun, allowing you to safely view the eclipse with the naked eye. At all other stages of the eclipse, it's essential to use solar eclipse glasses designed specifically for this purpose. Additionally, if you plan to use cameras, telescopes, or binoculars to enhance your viewing, ensure they are equipped with solar filters on their lenses at all times. This will protect both your eyes and the equipment from the sun's intense rays.
Photography: Photographing a solar eclipse requires some preparation and the right equipment to capture the event safely and effectively. Here are essential tips for photographing an eclipse:
1. Use Proper Solar Filters: Just like your eyes, your camera’s sensor needs protection from the sun’s harmful rays.
2. Equipment: Camera: A DSLR or mirrorless camera is ideal for capturing an eclipse; Lens: a telephoto Lens (200mm or longer) is recommended to get a detailed image of the Sun; Tripod: use a sturdy tripod to eliminate camera shake and maintain composition throughout the eclipse; Remote Shutter Release: To further reduce camera shake, use a remote shutter release or your camera's timer.
3. Practice and Plan: Practice your setup and know your equipment’s settings ahead of time.
4. Safety First: Never look through the camera’s viewfinder when pointing it towards the Sun unless you have a solar filter attached to the lens. Use the camera’s LCD screen or viewfinder for framing your shots when a filter is in place.
5. Bracket Your Shots: Light levels change rapidly during an eclipse. Use exposure bracketing to take multiple shots at different exposures to ensure you capture a well-exposed image.
6. Be Present: While it’s exciting to capture this astronomical event, remember to take some time to experience the eclipse with your own eyes (with proper eclipse glasses, of course, during everything but totality).
The Grand Eclipse of 2024… We are already coming to a conclusion of the first quarter of the 21st Century. As all previous early centuries, this one had been awaited with great expectations for dreamed advances to become reality.
Since its beginning and by April 8th of this year, 51 solar eclipses would have taken place; and 224 would have occurred by its end. On the other hand, since that initial mark and up to present, millions of people have died in violent conflict around the world. Others have survived the violence but have lost part of their bodies.. their arms, their legs, their eyes. They have lost their loved ones, too many or their most cherished dreams, perhaps even their desire to live ...the possibility or even the interest in looking at anything far out there on the sky or even right by their side.
This incomplete and imperfect article cannot then be but to be humbly dedicated to all people who talk sincerely about peace and who work to try to keep its possibility alive. If there is any value in it, it is -perhaps- the conviction behind it: that a Science that is not socially committed, more than useless, is dangerous… and that it is crucial to put it to work, always, for a peaceful and better world.
How to Photograph a Solar Eclipse, https://www.nikonusa.com/en/learn-and-explore/a/tips-and-techniques/how-to-photograph-a-solar-eclipse.html
March 25, 2024 — Penumbral Lunar Eclipse — New York, NY, USA, https://www.timeanddate.com/eclipse/in/usa/new-york?iso=20240325
Total Solar Eclipse, 2017 August 21st by Prof. Roman Senkov, https://www.flickr.com/photos/139707224@N04/albums/72157687944039406/
Where will the most crowded places be for the total solar eclipse 2024? https://www.space.com/most-crowded-places-for-total-solar-eclipse-april-2024
Total Solar Eclipse of 2024 Apr 08, https://eclipsewise.com/solar/SEprime/2001-2100/SE2024Apr08Tprime.html
US National Science Foundation [Large number of resources], https://nso.edu/for-public/eclipse-map-2024/ (very interesting interactive map. Click on any point to check details about the visibility of the eclipse from that place).
Detailed animation of the Moon shadow moving along the path of totality, https://www.greatamericaneclipse.com/april-8-2024
Detailed maps of the totality path, state by state, https://nationaleclipse.com/maps.html
Catalogue of Solar Eclipses of the 21st Century, https://eclipse.gsfc.nasa.gov/SEcat5/SE2001-2100.html
Other possible links
https://blogs.nasa.gov/Watch_the_Skies/2017/07/14/total-solar-eclipse-the-physics-of-light/