- Issue date: 02/02/2007
- Printing Process: Offset
- Paper: Autoadhesivo fosforescente
- Size of stamp: 40,9 x 28,8 mm. (horizontal) y 28,8 x 40,9 mm. (vertical)
- Sheet effects: 20
- Postal value of the stamps: 0,30 y 0,42 €
- Print run: Ilimitada para los dos valores postales
Within the science issue, two self adhesive stamps are launched, one devoted to Chemistry with the periodic table of elements of Mendeleyéiev and the other to Astronomy with the 425th Anniversary of the Gregorian calendar.
The first stamp refers to the periodic classification of the chemistry elements proposed by Dmitri Ivanovich Mendeleyéiev in 1869. As he attempted to classify the elements according to their chemical properties, he noticed patterns that led him to postulate his Periodic Table which described elements according to both weight and valence and which, if arranged according to their atomic mass, exhibited an apparent periodicity of properties. Unlike other contributors to the table he predicted the properties of elements yet to be discovered and made an accurate prediction of the qualities of germanium, gallium, and scandium which came to fill in the empty boxes of his table. Mendeleyéiev (1834-1907) made other important contributions to chemistry such as studies on the expansion of liquids with heat, the invention of pyrocollodion, a kind of smokeless powder based on nitrocellulose and made important contributions to the determination of the nature of such indefinite compounds as solutions. He was the author of Principles of Chemistry, a classic on the subject and for a couple of years was responsible for the Department of Weights and Measures of Saint Petersburg.
The second stamp is devoted to the Gregorian Calendar in its 425th Anniversary. This system was adopted by Pope Gregory XIII in 1582 because the mean year in the Julian Calendar was slightly too long, causing the vernal equinox to slowly drift backwards in the calendar year, and because the lunar calendar used to compute the date of Easter had grown conspicuously in error as well. If a year has approximately 365 days, 5 hours, 48 minutes and 98 hundredths of a second, it was decided to fix the year in 365 days and add one more every four years which would be a leap year. At that moment they were 10 days behind so it was decreed that the 4th of October 1582 was to be followed by Friday 15th of October and that in the future all years which were multiple of four were to be leap years, except those ended in two zeros, which would only be leap years when divisible by 400. The new calendar was adopted by the Catholic countries with mistrust since they believed this new system had taken away 10 days of their lives. The Gregorian Calendar is the one currently in force.