Frequently Asked Questions about Solar Eclipses
What is an eclipse of the Sun?
A solar eclipse occurs when the Moon passes between the Earth and Sun and the Moon's shadow crosses the Earth. From the Earth, the Moon and the Sun have almost the same diameter. Moreover, due to the distance variations betweem the Moon and the Earth, Moon can be seen from the Earth bigger or smaller than the Sun. This gives as a result the three types of eclipses: total, partial or annular.
Which characterístics have the different types of eclipses?
The Moon's orbit around the Earth is tilted 5 degrees to Earth's orbit around the Sun. A partial eclipse is when the Moon is not completely aligned with the Earth and the Moon. Part of the Earth is inside the shadow caused by the Moon, The Moon's shadow actually has two parts: Penumbra, that is the faint outer shadow, and the Umbra, the dark inner shadow. When only the Moon's penumbral shadow strikes Earth, we see a partial eclipse of the Sun from that region (see Fig, 1). All solar eclipses begin as partial as the Moon shadow is moving up to its maximum.
|Figure 1: Basic geometry of the Sun, Moon and Eath during a partial eclipse of the Sun. |
When the Moon is perfectly aligned between the Earth and the Sun, but the Moon is in the far side of its orbit, the Moon's umbral shadow is not long enough to reach Earth (see Fig, 2). This is called an annular solar eclipse. An observer located in the path of annularity will see an eclipse where a ring or "annulus" of bright sunlight surrounds the Moon at the maximum phase.
|Figure 2: Basic geometry of the Sun, Moon and Earth during an annular eclipse of the Sun. |
Finally, when the Moon is on the near side of its orbit, the Moon appears larger than the Sun. If an eclipse occurs at that time it will be a total eclipse of the Sun (see Fig. 3). Theses eclipses are very interesting. Besides looking directly at the Sun, as the direct light of the Sun is blocked some other rare phenomena can be watched. The first effect is the so called Bailly's beads. As the narrow crescent of the Sun finally begins to disappear, tiny specks of light remain visible for a few seconds more. These points of light are spaced irregularly around the disappearing edge of the Sun, forming the appearance of a string of beads around the dark disk of the Moon. The beads are actually the last few rays of sunlight shining through valleys on the edge of the Moon. Baily's beads make their brief appearance up to 15 seconds before totality. When a single point of sunlight remains, a beautiful "diamond ring" effect is created against the outline of the Moon. This final sparkling instant signals the arrival of the moon's shadow. The last ray of sunlight vanishes and totality begins. Against the backdrop of the white corona and the black disk of the Moon, two colorful effects are usually seen. First is the light from the Sun's lower atmosphere, the chromosphere. For a few seconds both after the beginning and before the end of totality, this pinkish glow appears at the edge of the Moon. Also often visible are several solar prominences. These red cloudlike appendages arch above the surface, reach a maximum height of nearly one-third the diameter of the Sun itself. Ussually this effects are not seen due to the bright light of the Sun, unless an eclipse occurr. Nowadays, there are instruments designed to produce this effect of blocking the Solar disc and thus, permitting the observation of the different levels of the atmosphere of the Sun (the chromosphere and the corona).
|Figure 3:Basic geometry of the Sun, Moon and Earth during a total eclipse of the Sun . |
Why don't eclipses ocurr every new Moon?
Eclipses only occur if the satellite of a planet is located within 0.5 degrees of the plane of the ecliptic, on a line that passes through the center of the Sun and Earth. The Moon travels along an orbit inclined by 5 degrees to the ecliptic plane, so there are only two opportunities each month -- when it passes through the plane of the ecliptic -- called the ascending and descending nodes. These two points connected to the barycenter of the Earth-Moon system (the point around which the objects orbit, in this case roughly Earth's center) define a 'line of nodes.' Eclipses of the Sun and Moon will occur if this line of nodes coincides with the line drawn between the center of Earth and the Sun. Again, the Moon also has to be within 0.5 degrees of one or the other of the nodes so that the disk of the Sun is partially or totally covered in a solar eclipse. A similar argument explains why lunar eclipses do not happen every full Moon at the node opposite the Sun from Earth. Decimos que la Luna se encuentra en fase de luna nueva cuando sólo recibe la luz del Sol por el lado opuesto a la Tierra, por lo tanto, en un eclipse de Sol siempre estaremos en fase de luna nueva. El motivo por el que no en todas las lunas nuevas hay un eclipse se debe a que la órbita de la Luna está ligeramente inclinada (5 grados y 6 minutos) respecto al plano Tierra-Sol. Por tanto la mayoría de las veces la luna nueva se sitúa en un plano diferente y es sólo cuando la luna nueva se produce en el plano Tierra-Sol, o muy cercano a éste, que se produce un eclipse de Sol.
How to observe a solar eclipse?
NEVER LOOK AT THE SUN DIRECTLY
Viewing of the Sun without suitable eye protection is EXTREMELY dangerous and can easily lead to total loss of eyesight. The retina does not have pain sensors, so you will not know that you are experiencing eye damage. Ensure that you have adequate eye protection (special eclipse viewing glasses, solar filters). More info here
Where in the Earth can we observe a solar eclipse?
In contrast with lunar eclipse, that can be viewed from everywhere in the Earth while night time, solar eclipses are only seen through very specific areas. Thus, the eclipse will be total (or annular) over a narrow corridor of a few hundreds of kilometers wide and a few thousands of kilometers corresponding to the path of the Moon shadow over the Earth. In a wider corridor the eclipse will be seen as partial.
Quan van ser els eclipsis anteriors a l'1 d'agost?
Some remarkable eclipses happened in the past are:
- 23 October 2014. Partial Solar Eclipse. Visibe from Est de Sibèria i Amèrica del Nord
- 29 April 2014. Annular Solar Eclipse de Sol. Visible from Antartida
- 09-10 May 2013. Annular Solar Eclipse d Sol. The annular path will pass throught NorthEast of Australia, and the Equatorial Pacific. It will be Partial over Hawaii, North New Zealand, Papua-New Guinea, Southern Philippines
- 3 November 2013. Annular-Total Solar Eclipse. Totality will pass through the Equatorial Pacific and Africa. In Catalonia will be visible as partial, almost imperceptible, 0.6%
- 21 May 2012. Annular Solar Eclipse. Visible from West of Xina, south Japan, West of the USA
- 13 November 2012. Eclipse total. Visible from Northest of Australia, South Pacific
- 4 January 2011. Partial Solar Eclipse. Visible afrom Europa, Africa, Asia.
- 1 June 2011. Partial Solar Eclipse. Visible from East Asia, Northern North America, Iceland.
- 1 July 2011. Partial Solar Eclipse. Visible from Southern Indian ocean
- 25 November 2011. Partial Solar Eclipse. Visible from Southern Africa, Antartica, Tasmania
- 11 July de 2010. Total Solar Eclipse. Visible from Pacific, Xile and Argentina.
- 15 January 2010. Annular Solar Eclipse. Visible from Asia and a large part of Africa.
- 22 July 2009. Annular Solar Eclipse. Visible from Indonesia.
- 26 January 2009. Total Solar Eclipse. Visible from India, Nepal, Xina and Pacific.
- 7 February 2008. Annular Solar Eclipse. Visible from some areas in Antarctica.
- 29 March 2006. Total Solar Eclipse. It was visible from the northern half of Africa, Turkey and some regions of Russia.
- 3 October 2005. Annular solar eclipse visible from Spain. The track of annularity/totality traversed the Iberian Peninsula from the Atlantic Ocean to introduce in Africa and ends in the Indian Ocean.
- 8 April 2005. It was an hybrid eclipse. It is to say that in some parts of the path it was annular and in others total. The track of annularity/totality traversed from the South Pacific Ocean to Central America. It was not observable from Europe.
- 23 November 2003. Total eclipse observable from Antarctica.
- 30 August 1905 and 17 April 1912. Last visible total and hybrid eclipses from Spain
- 8 juliy 1842. Last visible total eclipse from Catalonia.
When the next solar eclipses will happen? Some of the future relevant eclipses:
- 12 August 2026. Next total solar eclipse visible from Spain. It is observable in souther Catalonia.
- 26 January 2028. Next annular solar eclipse visible from Spain. It is observable in this phase from the Southwest of Catalonia.
What is the Saros cycle?
The Saros cycle exists because it takes 18 years and 10 days for the entire orbit of the Moon to precess once around in its orbit plane so that the lunar nodes make one complete revolution along the orbit. This "Nordical" period equals nearly an integer number of lunar months (223 x 29.53 days = 6,585.19 days) during each Saros cycle. Because the true length of the Saros cycle is 6,585.32 days, you have to wait three Saros cycles in order for a solar eclipse to repeat at the same spot on Earth. Successive eclipses in the Saros cycle happen one-third of the way around the world from each other, and after three Saros cycles, the eclipse returns to nearly the same geographic location after 54 years and 33 days. Twelve different Grand Saros eclipse series are now occurring, with the one producing the eclipses of 1937, 1955, 1973, 1991 and 2009, each having a duration near the 7.5 minute limit.