1. Petar Goulev, Milcho Tsvetkov, Renate Budell

3. Spectral observations of the Sun leading to discovery of Helium (1868)

4. ► ► Spectral observations of the Sun ► ► Discovered Helium in the Sun (1868) ► ► Nature of Sunspots and Solar Flares ► ► Determined the temperature of the Sun ► ► Founder of scientific journal “Nature”

5. ► ► 6,000 glass negatives ► ► Size: 81 x 30 mm or164x 81 mm ► ► Dates from 1880’s – 1950’s (Solar Physics Observatory, Norman Lockyer Observatory) ► ► Spectra of individual stars & clusters ► ► Spectra of Comets and Novae

6. Reproduced from “The Chemistry of the Sun” (1887)

7. ► A couple of two large refractors one of them fitted with an objective prisms. ► Made to Lockyer's specification (in 1885) ► In this second telescope starlight is split by a 52- degree prism in front of the objective lens

8.  Collection of plates of all the known elements, which Lockyer used to identify atoms present in the Sun.  A collection of spectra of 36 metallic elements made in 1874-1879 remains in our archives Edward Frankland

9. ► ► Antique plate ► ► Modern Plate

10. ► This plate contains the spectra of 25 stars.

11. ►

12. ► ► The timeframe in which the scanning could be done is essential ► ► Gelatine loses its properties ► ► Remaining fixing bath may destroy silver ► ► The chemical technology wasn’t developed in the beginning of the last century ► ► Underexposed ► ► Underdeveloped ► ► Faint as maximum density is below 1 ► ► Every transportation is a risk ► ► Furthermore the cost is very high and practically unaffordable

13. ► ► Microdensitometer ► ► Photometric Data System (PDS) - PDS 1010 ► ► Joyce Loebl ► ► Custom-designed scanner ► ► Digital Access to a Sky Century @ Harvard (DASCH) ► ► Super Cosmos ► ► Flatbed Scanner We used three different scanners manufactured by Epson ► ► Expression 10000 ► ► Expression 1640XL ► ► Perfection V700

14. ► ► Advantages ► ► Density mode D = 5.2 ► ► Resolution 5 µm in important for precise position of spectra lines ► ► Weakness ► ► depth of focus only few µm therefore bending of plates with long spectra could be unfocused

15. ► ► Advantages ► ► Scan more plates at once ► ► Automatically focus with large depths up to 1 mm ► ► Weaknesses ► ► Maximum density D ≤ 3 ► ► Spatial resolution 12 µm ► ► Density mode is impossible

16. ► ► Advantages ► ► Large focus depths up to 1 mm ► ► Lowest cost ► ► Weaknesses ► ► Maximum density D ≤ 3 ► ► No Autofocus

17. ► ► The problem with the historical plates is the low contrast and is better to use a transmission mode. ► ► PDS image is sharper, however flatbed scanner has a better contrast ratio ► ► For further and precise study of the absorption lines optimal resolution is required

18. ► ► Flatbed scanner should be used for a initial scanning of a spectral collection ► ► Microdensitometer scanner could be used only if the precise study is required ► ► The scanning has to be done sooner rather than later as the quality of the plates deteriorate. ► ► Some organisation would need a support to perform the scanning process.

19. ► ► Matching the referent spectral lines with the spectral plates require a specialised software, and could be difficult to achieve. ► ► There is a necessity of a specialised spectral database with meets the requirements of storing such data ► ► The owners of spectral plates archives have to be made aware of how important is to come forward, digitalise their plates and make them accessible on-line.

20. ► ► Thank you for your attention ► ► Благодаря за вниманието ► ► Хвала вам на пажњи ► ► With our presentation we would like to start a discussion for the future of the spectral plates stored into public and private archives across Europe and even worldwide.