© Lutfar Rahman Nirjhar. Image taken in July 2009.

Total solar eclipse

Mon, 21 Aug 2017 at14:26 EDT(4 days away)
18:26 UTC

Dominic Ford, Editor
From the Eclipses feed

Time:       Altitude: °      Azimuth: °

A simulation of how the eclipse will appear from Ashburn.


The Moon will pass in front of the Sun, creating a solar eclipse. From some parts of the world, the alignment will be so exact that the Moon will completely cover the Sun and the eclipse will be total.

The path of the total eclipse will pass through United States.

A partial eclipse will be seen from numerous other countries, including:

CountryExtent of eclipse
CanadaSun 89% covered
Cape VerdeSun 88% covered
BermudaSun 86% covered
BahamasSun 79% covered
Antigua and BarbudaSun 77% covered
Sint MaartenSun 77% covered
Saint BarthelemySun 77% covered
AnguillaSun 77% covered
Saint MartinSun 77% covered
British Virgin IslandsSun 76% covered

.

Eclipse alignment

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

Even when eclipses do occur, they are not visible from the whole world at once. The Moon casts a circular shadow onto the Earth, but because the Moon is much smaller than the Earth, the shadow doesn't cover the whole planet. Over time, the shadow sweeps across the Earth, so that different places see the eclipse at different times.

The eclipse path

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 the Sun's disk is 0% (red), 20%, 40%, 60% and 80% covered.

You can download this video in MP4 or OGG format.

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. The white contours within this show where the Moon appears to cover 20%, 40%, 60% and 80% of the Sun.

The white spot in the centre of the Moon's shadow traces out the thin eclipse track where a total eclipse will be seen.

From Ashburn (select a different location), the percentage of the Sun's disk covered by the Moon will proceed as follows:

13:20 EDT – 5%
13:30 EDT – 13%
13:40 EDT – 23%
13:50 EDT – 35%
14:00 EDT – 48%
14:10 EDT – 61%
14:20 EDT – 74%
14:30 EDT – 84%
14:40 EDT – 84%
14:50 EDT – 75%
15:00 EDT – 61%
15:10 EDT – 48%
15:20 EDT – 34%
15:30 EDT – 22%
15:40 EDT – 11%
15:50 EDT – 3%

As seen from any given location, this total eclipse will last for a maximum of 2 minutes.

Below, the path of the Moon's shadow is reprojected onto a flat map of the world. As before, the red contour shows the edge of the Moon's shadow, and encloses everywhere where the eclipse can be seen. The white contours show where the Sun is 20%, 40%, 60% and 80% covered.

You can download this video in MP4 or OGG format.

The map below shows a still image mapping the maximum extent of the eclipse across the world. The red contour encloses all places in which any part of the eclipse is visible.

Map of the total solar eclipse of August 2017

Eclipse safety

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 in which 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).

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 example of low-cost cardboard solar projection boxes. These two are sold in the UK by Green Witch.

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.

To my knowledge, the only UK supplier who sells these is Green Witch. They sell a Sun Projector Kit for £18, or a sturdier Lightec Solar Projection Telescope for £50.

Further details

This eclipse is a member of Saros series 145. The position of the Sun at the moment of greatest eclipse will be:

Object Right Ascension Declination Constellation Angular Size
Sun (centre) 10h03m +11°56' Leo 31'37"

The coordinates above are given in J2000.0.

The sky on 21 August 2017
Sunrise 06:27
Sunset 19:56
Twilight ends
21:33
Twilight begins
04:50

29-day old moon
Age of Moon
29 days

All times shown in EDT.
Rise Culm. Set
Mercury 07:23 13:40 19:57
Venus 03:38 10:54 18:09
Moon 06:23 13:09 19:55
Mars 05:45 12:41 19:38
Jupiter 10:43 16:23 22:04
Saturn 15:41 20:28 01:19

Warning

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.

Source

The simulations above were derived from the DE405 ephemeris published by the Jet Propulsion Laboratory (JPL). The position of the Moon's shadow is superimposed on maps of the world taken from the NASA Visible Earth project.

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:
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 In-The-Sky.org.

You can download them from:
https://in-the-sky.org/news/eclipses/solar_20170821_B.mp4
https://in-the-sky.org/news/eclipses/solar_20170821_A.mp4
https://in-the-sky.org/news/eclipses/solar_20170821.jpg

Related news

15 Aug 2017, 21:16 EDTMoon at Last Quarter
21 Aug 2017, 14:31 EDTNew Moon
29 Aug 2017, 04:14 EDTMoon at First Quarter
06 Sep 2017, 03:04 EDTFull Moon

Image credit

© Lutfar Rahman Nirjhar. Image taken in July 2009.

Ashburn

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