A helioscope is an instrument used in observing the sun

Sun

The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...

.
The helioscope was first used by Benedetto Castelli

Benedetto Castelli

Benedetto Castelli , born Antonio Castelli, was an Italian mathematician. He took the name "Benedetto" upon entering the Benedictine Order in 1595....

 (1578-1643) and refined by Galileo (1564–1642). The method involves projecting an image of the sun onto a white sheet of paper suspended in a darkened room with the use of a telescope.
http://brunelleschi.imss.fi.it/catalogo/genappr.asp?appl=SIM&xsl=approfondimento&lingua=ENG&chiave=100504

The first heliotropii telioscopici or helioscope was designed by Christoph Scheiner

Christoph Scheiner

Christoph Scheiner SJ was a Jesuit priest, physicist and astronomer in Ingolstadt....

 (1575 –1650) to assist his sunspot

Sunspot

Sunspots are temporary phenomena on the photosphere of the Sun that appear visibly as dark spots compared to surrounding regions. They are caused by intense magnetic activity, which inhibits convection by an effect comparable to the eddy current brake, forming areas of reduced surface temperature....

 observations.

See also

• Solar telescope
  Solar telescope
  A solar telescope is a special purpose telescope used to observe the Sun. Solar telescopes usually detect light with wavelengths in, or not far outside, the visible spectrum.-Professional solar telescopes:...
  
  
• Heliometer
  Heliometer
  Heliometer is an instrument originally designed for measuring the variation of the sun's diameter at different seasons of the year, but applied now to the modern form of the instrument which is capable of much wider use....
  
  
• Spectroheliograph
  Spectroheliograph
  The spectroheliograph is an instrument used in astronomy. It captures a photographic image of the Sun at a single wavelength of light, a monochromatic image...
  
  
• Spectrohelioscope
  Spectrohelioscope
  A spectrohelioscope is a type of solar telescope designed by George Ellery Hale in 1924 to allow the Sun to be viewed in a selected wavelength of light...