Spectroheliograph
Encyclopedia
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. The wavelength is usually chosen to coincide with an spectral wavelength of one of the chemical element
s present in the Sun.
It was developed independently by George Ellery Hale
and Henri-Alexandre Deslandres
in 1890 and further refined in 1932 by Robert R. McMath
to take motion pictures.
The instrument comprises a prism
or diffraction grating
, together with a narrow slit that passes a single wavelength (a monochromator
). The light is focus
ed onto a photographic medium and the slit is moved across the disk of the Sun to form a complete image.
It is now possible to make a filter
that transmits a narrow band of wavelengths which produces a similar image, but spectroheliographs remain in use.
Astronomy
Astronomy is a natural science that deals with the study of celestial objects and phenomena that originate outside the atmosphere of Earth...
. It captures a photographic
Photography
Photography is the art, science and practice of creating durable images by recording light or other electromagnetic radiation, either electronically by means of an image sensor or chemically by means of a light-sensitive material such as photographic film...
image of 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...
at a single wavelength
Wavelength
In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the wave's shape repeats.It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a...
of light
Light
Light or visible light is electromagnetic radiation that is visible to the human eye, and is responsible for the sense of sight. Visible light has wavelength in a range from about 380 nanometres to about 740 nm, with a frequency range of about 405 THz to 790 THz...
, a monochromatic image. The wavelength is usually chosen to coincide with an spectral wavelength of one of the chemical element
Chemical element
A chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus. Familiar examples of elements include carbon, oxygen, aluminum, iron, copper, gold, mercury, and lead.As of November 2011, 118 elements...
s present in the Sun.
It was developed independently by George Ellery Hale
George Ellery Hale
George Ellery Hale was an American solar astronomer.-Biography:Hale was born in Chicago, Illinois. He was educated at MIT, at the Observatory of Harvard College, , and at Berlin . As an undergraduate at MIT, he is known for inventing the spectroheliograph, with which he made his discovery of...
and Henri-Alexandre Deslandres
Henri-Alexandre Deslandres
Henri Alexandre Deslandres was a French astronomer, director of the Meudon and Paris Observatories.Deslandres' undergraduate years at the École Polytechnique were played out against the aftermath of the Franco-Prussian War and the chaos of the Paris Commune so, on graduation in 1874, he responded...
in 1890 and further refined in 1932 by Robert R. McMath
Robert Raynolds McMath
Robert Raynolds McMath was a U.S. solar astronomer.Robert R. McMath was a bridge engineer, businessman, and astronomer. Robert's father, Francis C. McMath, had made a fortune as a bridge builder. They both had a keen interest in amateur astronomy. So in 1922, the McMaths, along with Judge Henry S...
to take motion pictures.
The instrument comprises a prism
Prism (optics)
In optics, a prism is a transparent optical element with flat, polished surfaces that refract light. The exact angles between the surfaces depend on the application. The traditional geometrical shape is that of a triangular prism with a triangular base and rectangular sides, and in colloquial use...
or diffraction grating
Diffraction
Diffraction refers to various phenomena which occur when a wave encounters an obstacle. Italian scientist Francesco Maria Grimaldi coined the word "diffraction" and was the first to record accurate observations of the phenomenon in 1665...
, together with a narrow slit that passes a single wavelength (a monochromator
Monochromator
A monochromator is an optical device that transmits a mechanically selectable narrow band of wavelengths of light or other radiation chosen from a wider range of wavelengths available at the input...
). The light is focus
Focus (optics)
In geometrical optics, a focus, also called an image point, is the point where light rays originating from a point on the object converge. Although the focus is conceptually a point, physically the focus has a spatial extent, called the blur circle. This non-ideal focusing may be caused by...
ed onto a photographic medium and the slit is moved across the disk of the Sun to form a complete image.
It is now possible to make a filter
H-alpha
H-alpha is a specific red visible spectral line created by hydrogen with a wavelength of 656.28 nm, which occurs when a hydrogen electron falls from its third to second lowest energy level...
that transmits a narrow band of wavelengths which produces a similar image, but spectroheliographs remain in use.