English (UK)
Almeria, March 27th, 2025
Four solar eclipses will take place in Spain over less than three years: one partial eclipse (March 2025), two total eclipses (August 2026 and 2027), and one annular eclipse (January 2028). The last two will be ideally visible in a good part of Andalusia. This exceptional series of spectacular phenomena will attract millions of national and international visitors. It is a great opportunity to raise public awareness of astronomy.
However, observing a solar eclipse without protection represents a serious danger to the human eye: you should NEVER look directly at the Sun without proper equipment! Casual sunglasses do not provide the necessary protection.
In this press release, Calar Alto Observatory issues simple recommendations so that everyone can safely enjoy the great spectacle of Nature that a solar eclipse represents, starting with the partial eclipse of March 29th of this year.
The solar eclipse of March 29th, 2025, can be taken as the “appetizer” (a tapas) of the series of solar eclipses visible in Spain until 2028. It will be visible in the late morning, for less than two hours, all over the country. But it will be a very partial eclipse: only a small fraction of the solar disk, in its upper (Northern) part, will be hidden by the Moon, like a small bite given on the edge of Spanish tortilla, and it will be a very partial eclipse.
As a matter of fact, with the unaided eye, not even on a crystal clear day one could appreciate a change in the natural brightness of the Spanish sky, with slightly less than a third of the surface of the solar disk obscured in Galice, dropping to only a tenth of the solar disk in the Balearic Islands.
In the province of Almeria, the obscuration will not exceed 15% of the Sun's disk, starting at about 10:48 (Spanish peninsular winter time, UT+1) and ending at about 12:24, with the eclipse reaching its maximum at about 11:35.
NEVER observe the Sun directly without an adequate protection, either with the naked eye or with optical instruments (binoculars, spotting scopes or telescopes).
Map of Almeria with detailed data of the eclipse of March 29, 2025, for the Zapillo beach, extracted from the excellent Xavier Jubier’s website http://xjubier.free.fr/en/index_en.html
This Saturday, March 29th, a large number of people of all ages are expected to have free time to enjoy the sky. With this mini-eclipse, it will be possible to “rehearse” for the following, less partial ones, by scrupulously respecting one of these two safe methods:
1. Use solar eclipse glasses (solar viewers)
A direct visual observation must ALWAYS USE SPECIAL ECLIPSE GLASSES that follow the international standard EN ISO 12312-2:2015. It must be verified that they include the ISO/CE logos. Even so, you should rest your eyes after a few seconds looking at the Sun with eclipse glasses.
- These are afocal glasses only intended to filter sunlight for the bare eye; they can be placed in front of spectacles, but NEVER behind the eyepiece of a given optical instrument (not even theater binoculars).
- The frame (typically cardboard) of the eclipse glasses holds two oval apertures of a few centimeters with a sheet of special material (e.g., a polymer) of high optical density, filtering out almost all visible light from the Sun, as well as dangerous ultraviolet (UV) and infrared (IR) rays.
- Glasses should be checked for any apparent damage (not a single scratch on the filter) before being placed firmly in front of the eyes to look at the Sun.
- Do not try to reproduce very darkened “homemade” glasses by piling up sunglasses or undeveloped X-rays and photographic films, which allow non-visible rays (UV and IR) dangerous for the retina, cornea, and crystalline lens to pass through.
- It is preferable to buy eclipse glasses models of well-known optical brands, with a cost of a few euros per unit, in reliable physical or online stores. It is recommended to reject offers from unknown manufacturers, without the CE/ISO marking, which may be offered in street sales in the eclipse zones.
Left: For younger observers, check that the eclipse glasses cover the eyes well and do not slip. On the wall and the ground, you may appreciate the peculiar shape (crescent) of the shadow of the tree leaves. Partial phase of the July 2019 total eclipse in La Serena, Chile.
Right: Advanced partial phase observed by projection through a small spotting scope of 24 mm diameter and 5x magnification, inserted in the hole of a cardboard sheet to make a shadow and better see the image of the Sun projected on a white sheet on the ground. Partial phase of the August 2017 total eclipse in Saint-Louis, USA.
2. By projection (with or without optics)
For a safe indirect observation, without any special solar filter, the image of the Sun must be projected on a smooth surface (a wall, a table, or a sheet of paper on the ground).
- Without any optics, using the principle of the camera obscura: light is allowed to pass through a small hole made in an opaque material (e.g., perforated cardboard, thin sheet of wood or metal plate drilled) then a small image of the Sun is projected. Trees (when they have leaves, on March 29th not many will have grown yet) with their shadow produce a similar effect, with a multitude of “half moons” (actually, half suns) visible. Even kitchen utensils can be used, e.g. a strainer. Still, without any optics, the projected images of the Sun will be poorly defined.
- With small optical devices: binoculars or spotting scopes, restricting their aperture (cover + hole of 2 or 3 cm diameter at most) to limit the amount of incident light, which could damage the lenses or prisms. If they are oriented (looking for the smallest shadow) for a few seconds towards the Sun, one will see the image of our star projected on a smooth surface (again, the white sheet of paper is very useful). To improve visibility, the instrument can be surrounded by a sheet of paper/cardboard that creates a large shadow, facilitating the visibility of the projected solar disk. Using lenses allows to obtain a good size and more detailed projected image of the Sun (including possible sunspots). Still, be careful (with observers and instruments) due to the magnifying glass effect, which can even cause fires.
Our last recommendation is that the public DO NOT go up to Calar Alto, since these eclipses will NOT be better seen from the observatory: any place is fine, even in the middle of the city, as long as the Sun can be seen without being obscured by buildings, streetlights, trees, etc. and the phenomenon can be observed quietly. During the partial eclipse of March 29th, 2025, the Sun will be quite high (about 45º) in the sky, towards the southeast.
In any case, for every eclipse you must be cautious, standing in advance in a safe observation place (and it is better to be seated, the eclipse glasses do not let you see anything but the Sun), avoiding crowds and traffic jams to enjoy safely, responsibly and quietly the wonderful spectacles offered by our star throughout these three years in Spain.
From Calar Alto Observatory, in the next months we will keep informing about everything related to these solar eclipses, also through the observatory's social networks.
The Calar Alto Observatory is one of the infrastructures that belong to the national map of Unique Scientific and Technical Infrastructures (Spanish acronym: ICTS), approved on March 11th, 2022, by the Science, Technology and Innovation Policy Council (CPCTI).
CONTACT
Calar Alto Observatory - Gilles Bergond
COMMUNICATION - CALAR ALTO OBSERVATORY