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This is the second collaborative programme concerned with the observation of a Lunar Eclipse. The first programme of this kind was carried out very successfully in connection with the earlier lunar eclipse on September 27, 1996. In this programme, joint observations were made of the Lunar eclipse. Accurate timings, as well as a number of additional measurements, will allow your students to measure their accurate position on the Globe.
A preliminary report has now been prepared by Mogens Winther and his students (September 19, 1997)! Note in particular the impressive series made by Swedish observer Bengt Ask.
A lunar eclipse occurs when the Moon enters the Earth's shadow. 
During this
event, less sunlight reaches the Moon and its appearance changes.
During a Total Lunar Eclipse, the Moon is entirely inside the Earth's shadow; during a Partial Lunar Eclipse, only part of the Moon is inside.
A Lunar Eclipse always happens at the time of full moon, when the Sun, Earth and Moon are (nearly) aligned.
The following text describes the Total Lunar Eclipse of September 16, 1997. The historical importance of lunar eclipses when mapping the Earth is also described.
As you may find on e.g. the homepage by Byron W. Soulsby, Australia, this Lunar eclipse is visible in Europe, Australasia, Asia, except extreme N.E., the arctic regions, Antarctica and Africa except extreme West, in part in the Eastern areas and fully in the Western region of Australia.
This eclipse will happen shortly after sunset. When the full Moon is rising above central Europe, it will already be partially eclipsed.
During the totality, you will experience a strange sight, a beautiful deep-red full moon, placed below the bright stars of the huge Winter Square Pegasus-Andromeda. Northern Observers : The bright planet to the very right is Jupiter, the bright planet to the very left is Saturn.
Here, the time is indicated in Universal Time (UT), which is equal to British Winter Time. If you are located in another timezone, you must correct for the time difference in order to know the local time of the eclipse. For instance, observers in Central Europe must remember that the usual Summer Daylight Saving Time differs from Universal Time by +2 hours. An example: The Moon will leave totality at 19 hours 16 minutes UT. This is equal to 21 hours 16 minutes Central European Daylight Saving Time.
Lunar Eclipses like this one are global events which can be observed from any location on the earth were the moon is above the horizon. Contrarily, Total and Partial Solar Eclipses can only be seen from smaller regions.
This global visibility is the main reason, why Lunar Eclipses were important to Ancient Science.
The scientific belief that the Earth is a (round) sphere is more than 2500 years old. Scientists like the well-known Pythagoras(who lived at approximately 580 BC) concluded this directly by observing Lunar Eclipses. He observed the circular Earth shadow wander across the Moon, exactly as you will when you watch a lunar eclipse. The only object, which always gives a circular shadow, is a 3-dimensional sphere. Thus, the Earth must be round!
So, the Earth being a round Globe, it may be mapped in both East-West coordinates called Longitudes, and North-South coordinated called Latitudes.
Measuring these two coordinates in a reliable way is a must if you want to e.g. sail a ship across the Oceans, discover new continents, make discoveries.
Scientists like Eratosthenes, Hipparchos, Ptolemy, Plinius all remarked that in particular Lunar eclipses are a most powerful tool when mapping the Earth.
As described above, in Geography and Navigation, you need a parameter called the Geographical Longitude:
This Longitude was the often applied east-west division of our globe. For more than 1000 years, eclipses were the only reliable method to determine this longitude.
Plinius the Elder (AD 24-79) was an Admiral in the Roman Navy, and he had a strong interest in Science. In fact, he died due to this interest, being too close to the volcano Vesuvius during scientific investigations of the terrible eruptions that destroyed the city of Pompeii in AD 79.
Plinius wrote a famous book on General Science. In this he mentions one lunar eclipse in particular, that took place at the time of the battle of Arbela; this location is in present-day Iraq. During thisbattle, the moon was eclipsed, two hours after sunset. However, in Sicily, further to the west, the eclipse happened exactly at sunset.
This time difference of 2 hours thus tells that the distance between Arbela and Sicily is 2/24 of the circumference of the Earth. In our example above, Sicily and Arbela must then have a difference of longitude of 2/24 of 360 degrees = 30 degrees.
Based on such measurements, Ptolemy (140 AD) was able to publish quite good maps, showing both (East-West) Longitude and (North-South) Latitude.
Unfortunately, errorful measurements like those above made Ptolemy adopt an Earth circumference and radius that were about 30% too small. And this reduced size of the Earth was accepted without scepticism for more than 1000 years.
This finding of Ptolemy also did not leave much space for additional continents. The 1492 globe below, made the same year Columbus first sailed westwards in search of a new route to these countries, shows how India, Japan and China occupy the region that is now reserved for North and South America.
Globe by Martin Behaim from the year 1492, click for detail
Columbus did not know he had arrived at a new continent, then unknown in Europe. Until his death he firmly believed that the Islands on which he landed belonged to `West'-India.
A Lunar Eclipse that ocurred during his second voyage on September 14, 1494, could have shown Columbus that he had actually discovered a new continent. But unfortunately, he made a number of simple calculation errors. For more information, see for instance the student project article published in the September 1996 issue of the popular astronomy journal Sky & Telescope.
Another navigator-astronomer, Americo de Vespucci, made more careful observations during a voyage to the 'New World' in 1499. He discovered that 'West-India' was part of an entirely new continent, and this is one of the main reasons that this continent is now called America, and not Columbia.
Imagine that the moment of the end of totality of our eclipse is observed from both Greenwich (0 Longitude, a well known observatory outside London) and Bombay, India. That is, when the first spot on the Moon that is directly illuminated by the Sun, suddenly reappears.
In Greenwich, the total eclipse ended at 19 16 Local time - this is 07 hour 21 minutes after local noon ('local noon' is when the Sun is seen in the direction of South).
In Bombay, the total eclipse ends approximately 12 hours 12 minutes after local noon.
Calculate the difference (12h12m - 07h21m) in geographical longitude (in degrees) between these two cities, and compare with your map.
We suggest that you and your group participate actively by observing this Lunar Eclipse. Your subsequent report will be most welcome and should be submitted as indicated below.
Here are few remarks about these observations which may be useful for you and your group.
First you should note that the eclipsed Moon will not be completely dark; you will be able to see it all the time during the eclipse. Its colour will be dark red like it is shown on the figure above. This strange colour is the result of sunlight being refracted when it passes through the upper Earth atmosphere. Some of this light reaches the Moon. This is why the Moon is not completely dark, even when it iscompletely inside the Earth's geometric shadow.
Before the 1960s, Lunar Eclipses were therefore also a valuable means to investigate the conditions in the upper atmosphere of the Earth. For instance, due to the injected high-altitude dust in the Earth's atmopshere, the eclipsed Moon has a different colour during years of heavy vulcanic eruptions (Krakatau, Mount St. Helens, etc.), when compared to years with less vulcanic activity.
What to report:
Please try to observe
Calculate the difference between point 1 and point 2 - and compare it to the Greenwich values (exercise above). This will directly tell your own longitude with high precision ! Positional accuracy should be possible within a few kilometres !
Please try to observe
Our southern participants from e.g. Australia, are not able to observe this North Polar Star, and the Southern Cross is 30 Deg away from the South Celestial Pole.
However, in all cases, everybody should be able to measure
Drawings will be welcome too. By clicking on the line below you get the mailserver. Then write the information about your observations in the space reserved for the message.
Take a look at the webpage for this eclipse in Greece: http://www.astro.noa.gr/eclipse/ai-eclip.htm.
Moreover, you will find a continuously updated list of links with eclipse-related activities at http://www.amtsgym-sdbg.dk/as/eclinks.htm. In the morning of September 15, this page contained links to sites in Australia, Belgium, Denmark, Japan and the island of Reunion in the Indian Ocean, as well as others to various informative webpages on other continents. More may be added before the eclipse!
All observations of the Total Lunar Eclipse that are received from Astronomy On-Line Groups will be compared by the EAAE European Student Group. Some days later, they will be published in a joint article with tables in the Astronomy On-Line Newspaper, together with an evaluation of the results. Remember, your Group and your results will also be mentioned here, if you send in the measurements.
Thereafter you will be able to compute your geographical longitude by comparing your timing(s) with those of other groups, exactly as in the examples above. But now you have real, up-to-date data at your disposal.
How close will you come to the correct longitude/latitude ?
Have a nice time!
This project was prepared by the European Student Project Group of the European Association for Astronomy Education (EAAE):
| Josée Sert
(France)
Francis Berthomieu (France) Brian Stockwell (UK) Anders Västerberg (Sweden) Mogens Winther (Denmark) as well as our guest: Robert Hollow (Australia) |
The text here does not tell you everything about lunar eclipses , but if you want to know more, we suggest that you consult the Sky & Telescope Eclipse Pages which contain detailed predictions for the timing, advice about photographic work, etc. You will find very interesting information about other eclipses here as well, for instance about the total solar eclipse which can be seen in Europe on August 11, 1999. You may also look at the Sky & Telescope issues of September 1996 (page 68-71) or October 1992 (page 437).
You may also try the NASA Eclipses Home Page at http://planets.gsfc.nasa.gov/eclipse/eclipse.html.
Here are also suggestions for your own observations, and information about how you may determine your geographical longitude by comparing your observations with those obtained by other Astronomy On-Line Groups!
You can compare your results with those from observations of the Lunar Eclipse on September 27, 1996 by Astronomy On-Line Groups.
By simple drawings and measurements on this eclipse our students may perform reliable determination of the distance to the Moon. However, this is a bit more tricky, but do not hesitate to contact us. However, this method works best during partial eclipses, which may be observed from the very start to the very end
Similar projects were performed on the mentioned lunar and a solar eclipse last year. In the latter eclipse more than 50 schools and amateur groups contributed, and allowed an estimate of the Lunar distance within 5% of the official values.
You may also find it interesting to read about the ancient observations in a most fascinating science book: 'Science for the Citizen' by Lancelot Hogbein (Aberdeen, Sept. 1939).
And finally, if you are interested in the historical importance of Lunar and Solar eclipses, e.g. the dreadful eclipse-related death of General Gordon, then take a look at this account.
