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Partial solar eclipse

Dominic Ford, Editor
From the Eclipses feed

Simulation of the eclipse as seen from Cambridge
Time:       Altitude: °      Azimuth: °

The Moon will pass in front of the Sun, creating a partial eclipse of the Sun visible from Eastern Asia, United States, Northern Mariana Islands, Wake Island and Midway Islands between 18:34 and 22:48 EST.

The alignment between the Sun and Moon will not be very exact, and so the Moon will only partially cover the Sun, and nowhere on Earth will see a total eclipse.

The eclipse will not be visible from dry land, however, as its path will lie exclusively over the sea.

The simulation to the right shows how the eclipse will appear from Cambridge. The Sun is shown as the yellow disk at the center of the simulation, and the Moon is shown as the black disk which moves in front of the Sun. Both objects are of similar size – roughly 30 arcminutes across.

By default the simulation is drawn with the local vertical in Cambridge uppermost (Zenith up), so that it is orientated as you would see it looking up at the sky through an appropriate solar filter. The compass shows the direction of celestial north relative to the local vertical. Alternatively, you can orientate the Sun with celestial north orientated uppermost, by selecting the option North up.

Selecting the option Diagram of Moon's path produces a static display of the Moon's path over the duration of the eclipse.

The lower panel of the simulation shows the Sun's position relative to the horizon as seen from Cambridge.

The eclipse path

The map below shows the parts of the world where the eclipse will be visible, which are highlighted within the red contour. The yellow contours show the maximum extent of the eclipse, where the Moon appears to cover 20%, 40%, 60% and 80% of the Sun.

This map is also available as a KMZ file which can be imported into Google Earth, Google Maps, or other mapping software, and overlaid upon more detailed maps than the one shown below. Alternatively, the map can be downloaded as a non-interactive image in PNG, PDF or SVG formats.

The Moon's shadow projected onto the Earth as the eclipse proceeds. The hemisphere of the Earth facing the Sun is shown. Contours show where various fractions of the Sun's disk is covered.

You can download this video in MP4 or OGG format.

From Cambridge, the eclipse will not be visible, however. To see information about the times when the eclipse will be visible elsewhere in the world, select a different location.

The simulation to the right shows the path of the Moon's shadow across the Earth.

The red line shows the edge of the Moon's shadow: all places inside the red circle will see the Moon covering some part of the Sun's disk. Within this, contours show where various fractions of the Sun's disk is covered.

Below, an animation of the path of the Moon's shadow across the Earth's surface is projected onto map of the world. As above, the red contour shows the edge of the Moon's shadow, and encloses everywhere where the eclipse can be seen. Within this, yellow contours show where various fractions of the Sun's disk is covered.

You can download this video in MP4 or OGG format.

The eclipse geometry

The geometry of a solar eclipse
Solar eclipses take place when the Earth moves through the Moon's shadow. The dark gray cone behind the Moon indicates the region of space where the Moon appears to completely cover the Sun's disk (the Moon's umbra). The light gray area around it shows where the Moon appears to partially cover the Sun's disk (the Moon's penumbra).

Solar eclipses occur when the Sun, Moon and Earth are aligned in an almost exact straight line, with the Moon in the middle, such that the Moon passes in front of the Sun. The diagram to the right shows this geometry, though for clarity the Moon is drawn much closer to the Earth than it really is.

The Moon passes close to the Sun in the sky every month, at new moon, but because the Moon's orbit around the Earth is tipped up by 5° relative to the Earth's orbit around the Sun, the alignment usually isn't exact.

In the diagram below, the grid represents the plane of the Earth's orbit around the Sun. As it circles the Earth, the Moon passes through the Earth–Sun plane twice each month, at the points on the left and right labelled as nodes. A solar eclipse results when one of these node crossings happens to coincide with new moon, which happens roughly once every six months. At other times, the Moon typically passes a few degrees to the side of the Sun at new moon.

Even when a solar eclipse does occur, it will not be visible from the whole world.

The Moon is much smaller than the Earth, and so the shadow that it casts onto the Earth is never more than a few hundred miles across. As the Moon moves relative to us, the shadow sweeps across the Earth, so that different places see the eclipse at different times.

The Moon's orbit is tipped up by 5° relative to the Earth's orbit around the Sun, represented by the grid above. New moons only create solar eclipses if they occur when the Moon is close to the Earth–Sun plane, at points called the Moon's nodes.

The diagram below shows the Moon's shadow, with the Earth, Moon, and distance between them, drawn precisely to scale. The pink region shows the region of space where the Moon would appear to completely cover the Sun, creating a total solar eclipse. The blue region shows where the Moon would appear to partially cover the Sun, creating a partial solar eclipse.

The Earth is drawn twice on the right hand side, once at its closest possible distance from the Moon (left), and then again at its furthest possible distance from the Moon (right).

The cross marks the maximum distance from Moon at which a total eclipse is possible. Beyond this, the Moon appears too small to entirely cover the Sun.

For comparison, the geometry of lunar eclipses is also shown below: the Earth's shadow is by contrast to the Moon's shadow, amply large enough to cover the whole Moon at once, as happens in a total lunar eclipse.

The geometry of eclipses, shown to scale

Eclipse safety

Observing the Sun can be very dangerous if it is not done with the right equipment. The Sun is the brightest object in the sky, and looking directly at it can cause permanent eye damage within seconds. Viewing it through any optical instrument – even a pair of binoculars or the finderscope on the side of your telescope – can cause instant and permanent blindness.

If you have any doubts about whether your equipment is safe, it is best not to risk using it. By far the safest thing to do is to go along to a public observing event. Many astronomical societies are likely to be hosting observing events on the day, and they'll be sure to welcome newcomers. You may meet some new people at the same time as seeing the transit.

Many astronomy suppliers sell special special filters which are made for safe solar viewing. These include aluminised mylar filters, or black polymer filters, identified as suitable for direct viewing of the Sun. Check that the filter has a CE mark, and a statement that it conforms to European Community Directive 89/686/EEC. Alternatively, you can use a welder's glass rated at No. 14 or higher. Always read the manufacturer's instructions carefully.

Never attempt to make your own filter. In addition to visible light, the Sun also produces prodigious amounts of infrared and ultraviolet radiation which cannot be seen yet can still damage your eye. Even if a homebrew filter appears adequate, it may allow this unseen radiation to pass.

Projecting an image of the Sun

Two examples of low-cost cardboard solar projection boxes.

Another safe way to view solar eclipses is to buy a purpose-built solar projection box.

These typically consist of a cardboard box with a small lens on one side. They project an enlarged image of the Sun onto a white cardboard sheet inside the box. Once the transit is over, they're also great for observing sunspots. They are safe to use, quick to set up, and ideal for use with children and groups.

Further details

This eclipse is a member of Saros series 122. The position of the Sun at the moment of greatest eclipse will be:

Object Right Ascension Declination Constellation Angular Size
Sun (centre) 19h05m -22°34' Sagittarius 32'31"

The coordinates above are given in J2000.0.

The sky on 05 January 2019
Twilight ends
Twilight begins

29-day old moon
Waxing Crescent


29 days old

Rise Culm. Set
Mercury 06:19 10:47 15:16
Venus 03:30 08:31 13:32
Moon 06:52 11:31 16:10
Mars 10:49 16:56 23:02
Jupiter 04:51 09:30 14:08
Saturn 07:01 11:36 16:11
All times shown in EST.


Never attempt to point a pair of binoculars or a telescope at an object close to the Sun. Doing so may result in immediate and permanent blindness.


These eclipse predictions were computed using EclipseSimulator, an open-source tool for producing animations of eclipses written by the author and freely available for download.

They are based on the DE405 planetary ephemeris computed by the Jet Propulsion Laboratory (JPL). The position of the Sun, Earth and Moon were extracted from the DE405 files using EphemerisCompute, which was also written by the author, and is also freely available for download.

They assume that the Earth and Moon are both ellipsoids with fixed polar and equatorial radii, and do not take into account the irregular topography of either body. All eclipse predictions are made at sea level. In practice, this means that the predictions presented here are inaccurate by at most of few seconds.

The list of countries from which the eclipse is visible was computed on the basis of shape files available from DIVA-GIS.

Additional information was taken from:
[1] – Espanak, F., & Meeus, J., Five Millennium Canon of Solar Eclipses: -1999 to +3000, NASA Technical Publication TP-2006-214141 (2006)

You may embed the animations and images above in your own website. They are licensed under the Creative Commons Attribution 3.0 Unported license, which allows you to copy and/or modify them, so long as you credit

You can download them from:

Related news

05 Jan 2019  –  New Moon
05 Jan 2019  –  The Moon at perihelion
08 Jan 2019  –  The Moon at apogee
14 Jan 2019  –  Moon at First Quarter

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