Solar Eclipse: How it occurs

Solar Eclipse: How it occurs

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In relation to the image above, although the topic relates to math, how can I visualise the situation described in the final equation presented, i.e., the declinations, ascensions, solar and lunar radii. A diagram would be of great help.

For a small region not far from the equator, an equirectangular projection will do. If you want celestial north to be up, declination should increase from bottom to top, and right ascension should increase from right to left. To correct the aspect ratio, scale the RA axis by cos(dec). Then the sun and moon are circles of the respective angular radii, without the RA scale factor.

In the equation for $z$, $Delta$ is the declination of the sun, $delta$ is the declination of the moon, and $a$ is the difference in their right ascensions.

Solar Eclipse: How it occurs - Astronomy

An eclipse occurs when one object in space blocks an observer from seeing another object in space. From Earth there are two main types of eclipses: solar eclipses and lunar eclipses.

A solar eclipse occurs when the Moon passes in front of the Sun causing a shadow to fall on certain portions of the Earth. The eclipse is not seen from every place on Earth, but only from the locations where the shadow falls. From these locations, it appears as if the Sun has gone dark.

  • Umbra - The umbra is the portion of the Moon's shadow where the Moon completely covers the sun.
  • Antumbra - The area of the shadow beyond the point of the umbra. Here the Moon is completely in front of the Sun, but doesn't cover the entire Sun. The outline of the Sun can be seen around the shadow of the Moon.
  • Penumbra - The area of the shadow where only a portion of the Moon is in front of the Sun.

Types of Solar Eclipses

  • Total - A total eclipse is where the Sun is covered completely by the Moon. The portion of the Earth that is in the umbra experiences a total eclipse.
  • Annular - An annular eclipse is when the Moon covers the Sun, but the Sun can be seen around the edges of the Moon. An annular eclipse occurs when the viewer is within the antumbra.
  • Partial - A partial eclipse is when only a portion of the Sun is blocked by the Moon. It occurs when the observer is within the penumbra.

We should warn you here to never look directly at a solar eclipse. Even though it appears darker, the harmful rays of the Sun can still damage your eyes.

A lunar eclipse occurs when the Moon passes through the Earth's shadow. Lunar eclipses have the same three phases or types as solar eclipses including the umbra (total), antumbra (annular), and penumbra (partial).

Lunar eclipses can be seen by a much larger area of the Earth than solar eclipses. They also can be viewed without special equipment to protect the eyes. Lunar eclipses are not totally dark. The Moon will reflect some sunlight that is refracted by the Earth's atmosphere. The light that is refracted is reddish in color and can cause the Moon to appear a dark brownish-red.

Eclipses in Ancient Times

Eclipses have been tracked and recorded by astronomers since ancient times by such civilizations as the Ancient Babylonians and the Ancient Chinese. Eclipses were often thought to be signs from the gods.


There are four types of solar eclipses:

  • A total eclipse occurs when the dark silhouette of the Moon completely obscures the intensely bright light of the Sun, allowing the much fainter solar corona to be visible. During any one eclipse, totality occurs at best only in a narrow track on the surface of Earth. [6] This narrow track is called the path of totality. [7]
  • An annular eclipse occurs when the Sun and Moon are exactly in line with the Earth, but the apparent size of the Moon is smaller than that of the Sun. Hence the Sun appears as a very bright ring, or annulus, surrounding the dark disk of the Moon. [8]
  • A hybrid eclipse (also called annular/total eclipse) shifts between a total and annular eclipse. At certain points on the surface of Earth, it appears as a total eclipse, whereas at other points it appears as annular. Hybrid eclipses are comparatively rare. [8]
  • A partial eclipse occurs when the Sun and Moon are not exactly in line with the Earth and the Moon only partially obscures the Sun. This phenomenon can usually be seen from a large part of the Earth outside of the track of an annular or total eclipse. However, some eclipses can be seen only as a partial eclipse, because the umbra passes above the Earth's polar regions and never intersects the Earth's surface. [8] Partial eclipses are virtually unnoticeable in terms of the Sun's brightness, as it takes well over 90% coverage to notice any darkening at all. Even at 99%, it would be no darker than civil twilight. [9] Of course, partial eclipses (and partial stages of other eclipses) can be observed if one is viewing the Sun through a darkening filter (which should always be used for safety).

The Sun's distance from Earth is about 400 times the Moon's distance, and the Sun's diameter is about 400 times the Moon's diameter. Because these ratios are approximately the same, the Sun and the Moon as seen from Earth appear to be approximately the same size: about 0.5 degree of arc in angular measure. [8]

A separate category of solar eclipses is that of the Sun being occluded by a body other than the Earth's Moon, as can be observed at points in space away from the Earth's surface. Two examples are when the crew of Apollo 12 observed the Earth eclipse the Sun in 1969 and when the Cassini probe observed Saturn eclipsing the Sun in 2006.

The Moon's orbit around the Earth is slightly elliptical, as is the Earth's orbit around the Sun. The apparent sizes of the Sun and Moon therefore vary. [10] The magnitude of an eclipse is the ratio of the apparent size of the Moon to the apparent size of the Sun during an eclipse. An eclipse that occurs when the Moon is near its closest distance to Earth (i.e., near its perigee) can be a total eclipse because the Moon will appear to be large enough to completely cover the Sun's bright disk or photosphere a total eclipse has a magnitude greater than or equal to 1.000. Conversely, an eclipse that occurs when the Moon is near its farthest distance from Earth (i.e., near its apogee) can be only an annular eclipse because the Moon will appear to be slightly smaller than the Sun the magnitude of an annular eclipse is less than 1. [11]

A hybrid eclipse occurs when the magnitude of an eclipse changes during the event from less to greater than one, so the eclipse appears to be total at locations nearer the midpoint, and annular at other locations nearer the beginning and end, since the sides of the Earth are slightly further away from the Moon. These eclipses are extremely narrow in their path width and relatively short in their duration at any point compared with fully total eclipses the 2023 April 20 hybrid eclipse's totality is over a minute in duration at various points along the path of totality. Like a focal point, the width and duration of totality and annularity are near zero at the points where the changes between the two occur. [12]

Because the Earth's orbit around the Sun is also elliptical, the Earth's distance from the Sun similarly varies throughout the year. This affects the apparent size of the Sun in the same way, but not as much as does the Moon's varying distance from Earth. [8] When Earth approaches its farthest distance from the Sun in early July, a total eclipse is somewhat more likely, whereas conditions favour an annular eclipse when Earth approaches its closest distance to the Sun in early January. [13]

Terminology for central eclipse

Central eclipse is often used as a generic term for a total, annular, or hybrid eclipse. [14] This is, however, not completely correct: the definition of a central eclipse is an eclipse during which the central line of the umbra touches the Earth's surface. It is possible, though extremely rare, that part of the umbra intersects with the Earth (thus creating an annular or total eclipse), but not its central line. This is then called a non-central total or annular eclipse. [14] Gamma is a measure of how centrally the shadow strikes. The last (umbral yet) non-central solar eclipse was on April 29, 2014. This was an annular eclipse. The next non-central total solar eclipse will be on April 9, 2043. [15]

The phases observed during a total eclipse are called: [16]

  • First contact—when the Moon's limb (edge) is exactly tangential to the Sun's limb.
  • Second contact—starting with Baily's Beads (caused by light shining through valleys on the Moon's surface) and the diamond ring effect. Almost the entire disk is covered.
  • Totality—the Moon obscures the entire disk of the Sun and only the solar corona is visible.
  • Third contact—when the first bright light becomes visible and the Moon's shadow is moving away from the observer. Again a diamond ring may be observed.
  • Fourth contact—when the trailing edge of the Moon ceases to overlap with the solar disk and the eclipse ends.


The diagrams to the right show 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. [17]

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 a new moon occurs close to one of the points (known as nodes) where the Moon's orbit crosses the ecliptic. [18]

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. [19] [20]

Moon Sun
At perigee
At apogee
At perihelion
At aphelion
Mean radius 1,737.10 km
(1,079.38 mi)
696,000 km
(432,000 mi)
Distance 363,104 km
(225,622 mi)
405,696 km
(252,088 mi)
147,098,070 km
(91,402,500 mi)
152,097,700 km
(94,509,100 mi)
diameter [21]
33' 30"
29' 26"
32' 42"
31' 36"
Apparent size
to scale
Order by
apparent size
1st 4th 2nd 3rd

The Moon orbits the Earth in approximately 27.3 days, relative to a fixed frame of reference. This is known as the sidereal month. However, during one sidereal month, Earth has revolved part way around the Sun, making the average time between one new moon and the next longer than the sidereal month: it is approximately 29.5 days. This is known as the synodic month and corresponds to what is commonly called the lunar month. [18]

The Moon crosses from south to north of the ecliptic at its ascending node, and vice versa at its descending node. [18] However, the nodes of the Moon's orbit are gradually moving in a retrograde motion, due to the action of the Sun's gravity on the Moon's motion, and they make a complete circuit every 18.6 years. This regression means that the time between each passage of the Moon through the ascending node is slightly shorter than the sidereal month. This period is called the nodical or draconic month. [22]

Finally, the Moon's perigee is moving forwards or precessing in its orbit and makes a complete circuit in 8.85 years. The time between one perigee and the next is slightly longer than the sidereal month and known as the anomalistic month. [23]

The Moon's orbit intersects with the ecliptic at the two nodes that are 180 degrees apart. Therefore, the new moon occurs close to the nodes at two periods of the year approximately six months (173.3 days) apart, known as eclipse seasons, and there will always be at least one solar eclipse during these periods. Sometimes the new moon occurs close enough to a node during two consecutive months to eclipse the Sun on both occasions in two partial eclipses. This means that, in any given year, there will always be at least two solar eclipses, and there can be as many as five. [24]

Eclipses can occur only when the Sun is within about 15 to 18 degrees of a node, (10 to 12 degrees for central eclipses). This is referred to as an eclipse limit, and is given in ranges because the apparent sizes and speeds of the Sun and Moon vary throughout the year. In the time it takes for the Moon to return to a node (draconic month), the apparent position of the Sun has moved about 29 degrees, relative to the nodes. [2] Since the eclipse limit creates a window of opportunity of up to 36 degrees (24 degrees for central eclipses), it is possible for partial eclipses (or rarely a partial and a central eclipse) to occur in consecutive months. [25] [26]

During a central eclipse, the Moon's umbra (or antumbra, in the case of an annular eclipse) moves rapidly from west to east across the Earth. The Earth is also rotating from west to east, at about 28 km/min at the Equator, but as the Moon is moving in the same direction as the Earth's rotation at about 61 km/min, the umbra almost always appears to move in a roughly west–east direction across a map of the Earth at the speed of the Moon's orbital velocity minus the Earth's rotational velocity. [28] Rare exceptions can occur in polar regions where the path may go over or near the pole, as in 2021 on June 10 and December 4.

The width of the track of a central eclipse varies according to the relative apparent diameters of the Sun and Moon. In the most favourable circumstances, when a total eclipse occurs very close to perigee, the track can be up to 267 km (166 mi) wide and the duration of totality may be over 7 minutes. [29] Outside of the central track, a partial eclipse is seen over a much larger area of the Earth. Typically, the umbra is 100–160 km wide, while the penumbral diameter is in excess of 6400 km. [30]

Besselian elements are used to predict whether an eclipse will be partial, annular, or total (or annular/total), and what the eclipse circumstances will be at any given location. [31] : Chapter 11 Calculations with Besselian elements can determine the exact shape of the umbra's shadow on the Earth's surface. But at what longitudes on the Earth's surface the shadow will fall, is a function of the Earth's rotation, and on how much that rotation has slowed down over time. A number called ΔT is used in eclipse prediction to take this slowing into account. As the Earth slows, ΔT increases. ΔT for dates in the future can only be roughly estimated because the Earth's rotation is slowing irregularly. This means that, although it is possible to predict that there will be a total eclipse on a certain date in the far future, it is not possible to predict in the far future exactly at what longitudes that eclipse will be total. Historical records of eclipses allow estimates of past values of ΔT and so of the Earth's rotation.


The following factors determine the duration of a total solar eclipse (in order of decreasing importance): [32] [33]

  1. The Moon being almost exactly at perigee (making its angular diameter as large as possible).
  2. The Earth being very near aphelion (furthest away from the Sun in its elliptical orbit, making its angular diameter nearly as small as possible).
  3. The midpoint of the eclipse being very close to the Earth's equator, where the rotational velocity is greatest.
  4. The vector of the eclipse path at the midpoint of the eclipse aligning with the vector of the Earth's rotation (i.e. not diagonal but due east).
  5. The midpoint of the eclipse being near the subsolar point (the part of the Earth closest to the Sun).

The longest eclipse that has been calculated thus far is the eclipse of July 16, 2186 (with a maximum duration of 7 minutes 29 seconds over northern Guyana). [32]

Total solar eclipses are rare events. Although they occur somewhere on Earth every 18 months on average, [35] it is estimated that they recur at any given place only once every 360 to 410 years, on average. [36] The total eclipse lasts for only a maximum of a few minutes at any location, because the Moon's umbra moves eastward at over 1700 km/h. [37] Totality currently can never last more than 7 min 32 s. This value changes over the millennia and is currently decreasing. By the 8th millennium, the longest theoretically possible total eclipse will be less than 7 min 2 s. [32] The last time an eclipse longer than 7 minutes occurred was June 30, 1973 (7 min 3 sec). Observers aboard a Concorde supersonic aircraft were able to stretch totality for this eclipse to about 74 minutes by flying along the path of the Moon's umbra. [38] The next total eclipse exceeding seven minutes in duration will not occur until June 25, 2150. The longest total solar eclipse during the 11,000 year period from 3000 BC to at least 8000 AD will occur on July 16, 2186, when totality will last 7 min 29 s. [32] [39] For comparison, the longest total eclipse of the 20th century at 7 min 8 s occurred on June 20, 1955, and there are no total solar eclipses over 7 min in duration in the 21st century. [40]

It is possible to predict other eclipses using eclipse cycles. The saros is probably the best known and one of the most accurate. A saros lasts 6,585.3 days (a little over 18 years), which means that, after this period, a practically identical eclipse will occur. The most notable difference will be a westward shift of about 120° in longitude (due to the 0.3 days) and a little in latitude (north-south for odd-numbered cycles, the reverse for even-numbered ones). A saros series always starts with a partial eclipse near one of Earth's polar regions, then shifts over the globe through a series of annular or total eclipses, and ends with a partial eclipse at the opposite polar region. A saros series lasts 1226 to 1550 years and 69 to 87 eclipses, with about 40 to 60 of them being central. [41]

Frequency per year

Between two and five solar eclipses occur every year, with at least one per eclipse season. Since the Gregorian calendar was instituted in 1582, years that have had five solar eclipses were 1693, 1758, 1805, 1823, 1870, and 1935. The next occurrence will be 2206. [42] On average, there are about 240 solar eclipses each century. [43]

The 5 solar eclipses of 1935
January 5 February 3 June 30 July 30 December 25

Saros 111

Saros 149

Saros 116

Saros 154

Saros 121

Final totality

Total solar eclipses are seen on Earth because of a fortuitous combination of circumstances. Even on Earth, the diversity of eclipses familiar to people today is a temporary (on a geological time scale) phenomenon. Hundreds of millions of years in the past, the Moon was closer to the Earth and therefore apparently larger, so every solar eclipse was total or partial, and there were no annular eclipses. Due to tidal acceleration, the orbit of the Moon around the Earth becomes approximately 3.8 cm more distant each year. Millions of years in the future, the Moon will be too far away to fully occlude the Sun, and no total eclipses will occur. In the same timeframe, the Sun may become brighter, making it appear larger in size. [44] Estimates of the time when the Moon will be unable to occlude the entire Sun when viewed from the Earth range between 650 million [45] and 1.4 billion years in the future. [44]

Historical eclipses are a very valuable resource for historians, in that they allow a few historical events to be dated precisely, from which other dates and ancient calendars may be deduced. [46] A solar eclipse of June 15, 763 BC mentioned in an Assyrian text is important for the chronology of the ancient Near East. [47] There have been other claims to date earlier eclipses. The Book of Joshua 10:13 describes the sun staying still for an entire day in the sky a group of University of Cambridge scholars concluded this to be the annular solar eclipse that occurred on 30 October 1207 BC. [48] The Chinese king Zhong Kang supposedly beheaded two astronomers, Hsi and Ho, who failed to predict an eclipse 4,000 years ago. [49] Perhaps the earliest still-unproven claim is that of archaeologist Bruce Masse, who putatively links an eclipse that occurred on May 10, 2807 BC with a possible meteor impact in the Indian Ocean on the basis of several ancient flood myths that mention a total solar eclipse. [50]

Eclipses have been interpreted as omens, or portents. [51] The ancient Greek historian Herodotus wrote that Thales of Miletus predicted an eclipse that occurred during a battle between the Medes and the Lydians. Both sides put down their weapons and declared peace as a result of the eclipse. [52] The exact eclipse involved remains uncertain, although the issue has been studied by hundreds of ancient and modern authorities. One likely candidate took place on May 28, 585 BC, probably near the Halys river in Asia Minor. [53] An eclipse recorded by Herodotus before Xerxes departed for his expedition against Greece, [54] which is traditionally dated to 480 BC, was matched by John Russell Hind to an annular eclipse of the Sun at Sardis on February 17, 478 BC. [55] Alternatively, a partial eclipse was visible from Persia on October 2, 480 BC. [56] Herodotus also reports a solar eclipse at Sparta during the Second Persian invasion of Greece. [57] The date of the eclipse (August 1, 477 BC) does not match exactly the conventional dates for the invasion accepted by historians. [58]

Chinese records of eclipses begin at around 720 BC. [59] The 4th century BC astronomer Shi Shen described the prediction of eclipses by using the relative positions of the Moon and Sun. [60]

Attempts have been made to establish the exact date of Good Friday by assuming that the darkness described at Jesus's crucifixion was a solar eclipse. This research has not yielded conclusive results, [61] [62] and Good Friday is recorded as being at Passover, which is held at the time of a full moon. Further, the darkness lasted from the sixth hour to the ninth, or three hours, which is much, much longer than the eight-minute upper limit for any solar eclipse's totality. Contemporary chronicles wrote about an eclipse at the beginning of May 664 that coincided with the beginning of the plague of 664 in the British isles. [63] In the Western hemisphere, there are few reliable records of eclipses before AD 800, until the advent of Arab and monastic observations in the early medieval period. [59] The Cairo astronomer Ibn Yunus wrote that the calculation of eclipses was one of the many things that connect astronomy with the Islamic law, because it allowed knowing when a special prayer can be made. [64] The first recorded observation of the corona was made in Constantinople in AD 968. [56] [59]

The first known telescopic observation of a total solar eclipse was made in France in 1706. [59] Nine years later, English astronomer Edmund Halley accurately predicted and observed the solar eclipse of May 3, 1715. [56] [59] By the mid-19th century, scientific understanding of the Sun was improving through observations of the Sun's corona during solar eclipses. The corona was identified as part of the Sun's atmosphere in 1842, and the first photograph (or daguerreotype) of a total eclipse was taken of the solar eclipse of July 28, 1851. [56] Spectroscope observations were made of the solar eclipse of August 18, 1868, which helped to determine the chemical composition of the Sun. [56]

John Fiske summed up myths about the solar eclipse like this in his 1872 book Myth and Myth-Makers,

the myth of Hercules and Cacus, the fundamental idea is the victory of the solar god over the robber who steals the light. Now whether the robber carries off the light in the evening when Indra has gone to sleep, or boldly rears his black form against the sky during the daytime, causing darkness to spread over the earth, would make little difference to the framers of the myth. To a chicken a solar eclipse is the same thing as nightfall, and he goes to roost accordingly. Why, then, should the primitive thinker have made a distinction between the darkening of the sky caused by black clouds and that caused by the rotation of the earth? He had no more conception of the scientific explanation of these phenomena than the chicken has of the scientific explanation of an eclipse. For him it was enough to know that the solar radiance was stolen, in the one case as in the other, and to suspect that the same demon was to blame for both robberies. [65]

Looking directly at the photosphere of the Sun (the bright disk of the Sun itself), even for just a few seconds, can cause permanent damage to the retina of the eye, because of the intense visible and invisible radiation that the photosphere emits. This damage can result in impairment of vision, up to and including blindness. The retina has no sensitivity to pain, and the effects of retinal damage may not appear for hours, so there is no warning that injury is occurring. [66] [67]

Under normal conditions, the Sun is so bright that it is difficult to stare at it directly. However, during an eclipse, with so much of the Sun covered, it is easier and more tempting to stare at it. Looking at the Sun during an eclipse is as dangerous as looking at it outside an eclipse, except during the brief period of totality, when the Sun's disk is completely covered (totality occurs only during a total eclipse and only very briefly it does not occur during a partial or annular eclipse). Viewing the Sun's disk through any kind of optical aid (binoculars, a telescope, or even an optical camera viewfinder) is extremely hazardous and can cause irreversible eye damage within a fraction of a second. [68] [69]

Is it safe to photograph a solar eclipse?

Yes, but you must be very careful. All phases of this eclipse from everywhere on the planet must be viewed through solar filters—and that goes double for cameras. If you’re using a camera and a lens, or a telescope or a pair of binoculars, then they must have a solar filter or solar film over the front (and not over the eyepiece or viewfinder!). Why? The Sun’s infrared and ultraviolet rays are incredibly dangerous and can damage your eyesight without you feeling any pain. If you’ve not got any solar filters or solar film, don’t photograph the eclipse!

  • use eclipse glasses to look at the eclipse.
  • put solar filters on the front of any telescope, binoculars or camera lens.
  • put eclipse glasses over a smartphone’s camera lens.
  • don’t look through a camera’s optical viewfinder—use the LCD screen.

Circumstances around the planet

CitySunrise/sunsetMax. eclipseObscurationAlt.End of eclipse
Fairbanks, AK3:09 a.m.2:50 a.m.50.1% at sunrise–0.3°3:44 a.m.
Thunder Bay, ON5:56 a.m.5:53 a.m.85.4% at sunrise–0.3°6:50 a.m.
Chicago, IL5:16 a.m.4:44 a.m.28.8% at sunrise–0.3°5:39 a.m.
Detroit, MI5:56 a.m.5:41 a.m.60.6% at sunrise–0.3°6:38 a.m.
Ottawa, ON5:40 a.m.80.1%3.2°6:40 a.m.
Quebec City, PQ5:40 a.m.78.9%6.5°6:41 a.m.
Pittsburgh, PA5:50 a.m.5:36 a.m.60.7% at sunrise–0.3°6:33 a.m.
Charlotte, NC6:09 a.m.5:31 a.m.16.8% at sunrise–0.3°6:26 a.m.
New York, NY5:33 a.m.72.5%6:31 a.m.
Cambridge, MA5:33 a.m.72.9%3.5°6:33 a.m.
Reykjavik, IS10:17 a.m.60.5%38.5°11:33 a.m.
Dublin, IE11:09 a.m.28.5%50.3°12:22 p.m.
London, UK11:13 a.m.20.0%54.9°12:23 p.m.
Madrid, ES11:43 a.m.4.8%53.9°12:29 p.m.
Venice, IT12:26 p.m.2.2%65.9°1:05 p.m.
Vienna, AT12:40 p.m.4.4%64.7°1:28 p.m.
Helsinki, FI2:04 p.m.26.8%52.1°3:15 p.m.
Moscow, RU2:26 p.m.15.7%50.8°3:28 p.m.
Beijing, CN7:43 p.m.8:19 p.m.7.6% at sunset–0.3°
This table includes a sample of cities where the partial solar eclipse will be visible. All times are local. Sunrise occurs when the upper limb of the Sun first appears at the horizon. Sunrise/sunset times are listed where relevant. Altitude values include the effects of atmospheric refraction. For cities where the maximum viewable eclipse occurs at sunup, the amount of obscuration will be several percent less than the values shown once the solar disk clears the horizon approximately 4 minutes later.
Source: Xavier M. Jubier

For now, I'm aware of two livestreams (below) for watching the eclipse online. If you hear of others, please let me know, and I'll add them. Check here for solar eclipse photo tips, and remember to share the event with family and friends. It feels good to finally come out of our COVID-19 shells into the sunshine.

The Sun rises in annular eclipse on May 10, 2013, as seen from Western Australia. Note the slight elongation of the Sun’s disk and the lunar silhouette due to atmospheric refraction near the horizon. Telescope users in or near the path of annularity should watch for weird diffraction effects as lunar peaks "stretch" towards the Sun's inner limb at second and third contacts, when the lunar limb is tangent to the Sun's inner limb. Prominences might also be photographed at these times.
Geoff Sims & Colin Legg YouTube starts June 10th, 3 a.m. CDT (8:00 UT)
CosmoSapiens YouTube, starts June 10th, 2 a.m. CDT (7:00 UT)
Virtual Telescope with Gianluca Masi, starts June 10th, 4:30 a.m. CDT (9:30 UT)

If you're interested in reading more about this and other celestial events this month click here to purchase a copy of the June 2021 issue of Sky & Telescope.

Solar Eclipse

A solar eclipse is an event that occurs when the Moon passes between the Earth and the Sun, partially or totally blocking the sunlight.

A solar eclipse is an event that occurs when sunlight does not reach Earth because it is totally or partially blocked by the Moon. Even though the Moon is many times smaller than the Sun, they can appear to be the same size in the sky because the Moon is so much closer. There are three types of eclipses and between two and five eclipses occur every year.

A total eclipse occurs when the Sun is completely obscured by the Moon. This only occurs when the Sun is far away or the Moon is close to Earth and is viewed from the umbra region, where the shadow is the darkest. A partial eclipse can occur when viewed from the penumbra area and the Sun is partially blocked by the Moon. A third type of eclipse is known as an annular eclipse. An annular eclipse occurs when the Moon is far away from Earth or the Sun is very close. The Moon doesn’t appear large enough in the sky to cover the Sun completely the Sun appears as a bright ring in the sky.

Eclipses are significant for historians as they are normally well reported and can be dated precisely. Some historians believe a solar eclipse occurred on Good Friday as people reported that there was darkness during the crucifixion of Jesus. An eclipse is a natural phenomenon that has occurred many times, but earlier civilizations who didn’t understand the science behind them often associated them with bad omens and relied on supernatural explanations. The total eclipse of 1919 was used to provide data to support Einstein’s theory of relativity. The eclipse provided an opportunity for scientists to observe light bending around our Sun.

Observing solar eclipses can be dangerous if you don’t use the correct protective equipment because permanent damage can occur to the retina, which could lead to blindness. While indirect sunlight normally does no harm to the cells in our retina, direct sunlight when focused onto our retinas can cause permanent damage to the cells there.

How Do I Use This?

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Use these encyclopedias as a springboard for individual and class-wide projects!

Lunar Eclipses

A lunar eclipse occurs when the Moon passes through the Earth's shadow. Because the Earth is much larger than the Moon, usually the entire Moon is eclipsed. Because the full phase can be seen from anywhere on the night side of the Earth, a lunar eclipse can be seen by more people than a solar eclipse. Since the Moon is moving through the Earth's shadow, and the size of the Earth is much greater than the size of the Moon, a lunar eclipse last for about 3.5 hours (as opposed to a solar eclipse which last on the order of about 7.5 minutes).

To learn more about lunar eclipses, see pictures of actual eclipses, and find out when the next lunar eclipse will occur, click here.

Teacher Resources

A solar eclipse is a unique chance to engage students in first-hand astronomy. Simple activities like building projection viewers with a cereal-box or hole-punched card, and exploring the scale of the Sun and Moon through observation and eclipse modeling, are great ways to introduce the subject in the classroom. More in-depth lessons that replicate the Moon phases can help students understand why and how eclipses happen. Encourage students and their families to find easy and safe ways to observe the eclipse, whether from home or at school. There are more educator resources available from NASA and the National Science Teachers Association (NSTA).

Solar Eclipse: How it occurs - Astronomy

Courtesy: Discover the Universe

FOR IMMEDIATE RELEASE – The Dunlap Institute for Astronomy & Astrophysics and Discover the Universe have been working on sharing educational information and safety glasses in preparation for the June 10, 2021 Solar Eclipse.

An Annular Solar Eclipse will take place in the early morning hours of June 10, and is best viewed in Ontario, Quebec, and Nunavut. An ‘annular’ eclipse occurs as the moon passes in front of the sun, causing a ring of light to appear in the sky. Solar eclipses happen about once or twice a year, but this one is unique to our part of the world. Due to the nature of an annular eclipse, safety viewing glasses (or eclipse glasses) are required for direct observation. The visible light from the sun can cause ocular damage if looked at directly. More Information.

Beginning in February, the Dunlap Institute and Discover the Universe began preparing for the eclipse by ordering safety glasses to give away to anyone in the areas where the eclipse would best be observed (the path of annularity). Discover the Universe, being an educational program, also prepared kits to mail out to people in remote communities. Learn more.

In April, we mailed out 267 educational kits to communities within the path of annularity, delivering them to schools, classrooms, and community groups. There was such interest in safety glasses, that Discover the Universe decided to launch an Eclipse Challenge! Members of the public are being challenged to use a projection method to safely observe the eclipse even without glasses. By letting the sunlight pass through a hole, onto a screen, the eclipse can be seen without directly looking at it.

Contact Info:

Mike Reid
Public Outreach Coordinator, Dunlap Institute for Astronomy & Astrophysics
Phone: +1 647-638-9001
Email: [email protected]
Julie Bolduc-Duval
Executive Director, Discover the Universe
Phone: +1 418-332-0428
Email: [email protected]

Founded in 2011, Discover the Universe provides free training and resources in astronomy for teachers and educators nation-wide.

The Dunlap Institute for Astronomy & Astrophysics at the University of Toronto is an endowed research institute with more than 90 faculty, postdocs, students and staff, dedicated to innovative technology, ground-breaking research, world-class training, and public engagement. The research themes of its faculty and Dunlap Fellows span the Universe and include: optical, infrared and radio instrumentation Dark Energy large-scale structure the Cosmic Microwave Background the interstellar medium galaxy evolution cosmic magnetism and time-domain science. The Dunlap Institute for Astronomy and Astrophysics, David A. Department of Astronomy & Astrophysics and the Canadian Institute for Theoretical Astrophysics comprise the leading centre for astronomical research in Canada, at the leading research university in the country, the University of Toronto.

How Solar Eclipses Work

A solar eclipse is a celestial phenomenon that does not occur very often, but they are fascinating to watch when they do. On those rare occasions when you are in the right place at the right time for a full solar eclipse, it is amazing.

In this article, we will see what happens during a solar eclipse and how you can observe this incredible event safely.

What Is a Solar Eclipse?

A solar eclipse occurs when the moon passes in a direct line between the Earth and the sun. The moon's shadow travels over the Earth's surface and blocks out the sun's light as seen from Earth.

Because the moon orbits the Earth at an angle, approximately 5 degrees relative to the Earth-sun plane, the moon crosses the Earth's orbital plane only twice a year. These times are called eclipse seasons, because they are the only times when eclipses can occur. For an eclipse to take place, the moon must be in the correct phase during an eclipse season for a solar eclipse, it must be a new moon. This condition makes solar eclipses relatively rare.

Types of Solar Eclipses

The moon's shadow has two parts: a central region (umbra) and an outer region (penumbra). Depending upon which part of the shadow passes over you, you will see one of three types of solar eclipses:

  • Total - The entire central portion of the sun is blocked out.
  • Partial - Only part of the sun's surface is blocked out.
  • Annular - Only a small, ring-like sliver of light is seen from the sun's disc.

If the umbra passes over you, the entire central portion of the sun will be blocked out. You will see a total solar eclipse, and the sky will darken as if it were night time. During a total solar eclipse, you can see the sun's outer atmosphere, called the corona. In fact, this is the only time that you can see the corona, which is why astronomers get so excited when a total eclipse is about to occur. Many astronomers travel the world chasing eclipses.

If the penumbra passes over you, only part of the sun's surface will be blocked out. You will see a partial solar eclipse, and the sky may dim slightly depending on how much of the sun's disc is covered.

In some cases, the moon is far enough away in its orbit that the umbra never reaches the Earth at all. In this case, there is no region of totality, and what you see is an annular solar eclipse. In an annular eclipse, only a small, ring-like sliver of light is seen from the sun's disc ("annular" means "of a ring").

How to Watch a Solar Eclipse

Never look at the sun directly -- doing so can damage your eyes. The best way to observe the sun is by projecting the image. Here is one way to project the sun's image:

  1. Get two pieces of cardboard (flaps from a box, backs of paper tablets).
  2. With a pin or pencil point, poke a small hole in the center of one piece (no bigger than the pin or pencil point).
  3. Take both pieces in your hand.
  4. Stand with your back to the sun.
  5. In one hand, hold the piece with the pinhole place the other piece (the screen) behind it.
  6. The sunlight will pass through the pinhole and form an image on the screen (see How does a pinhole camera work? for details on this process).
  7. Adjust the distance between the two pieces to focus and change the size of the image.

For more information on solar eclipses and related topics, check out the links that follow.