The Hubble Space Telescope, launched in 1990, provided a revolutionary turning point in space research. In orbit, uninterrupted by Earth’s atmosphere, this space telescope transmits high-resolution astronomical images to Earth, physically continuing the achievements of astronomer Edwin Hubble, who discovered the expansion of the universe. Hubble dramatically expanded our scientific understanding of the universe by recording in detail the processes of galaxy formation and extinction, complex phenomena around black holes, and the evolution of stars. This space telescope plays an important role in continuous exploration of the unknown areas of the universe and in arousing the scientific curiosity of people on Earth.
▲ CCD specially developed with wire bonded package used for ultraviolet imaging. Source: Wikipedia
The Hubble Space Telescope is built around a 2.4-meter-diameter high-reflectivity mirror and a sophisticated optical system, through which it clearly captures light from space. Various measuring instruments, CCD cameras, spectrometers, and various filters mounted on the telescope analyze the wavelength and characteristics of light to generate high-resolution space images and data. These instruments are used to study the chemical composition of stars, the distances of galaxies, and the composition of planets’ atmospheres, and are used as key data for astronomical discoveries.
The Hubble Telescope is equipped with several instruments to perform various observation purposes, including the Wide Field and Planetary Camera 2 (WFPC2) and the Near Infrared Camera and Multi-Object Spectrometer (NICM OS). , Advanced Camera a for Surveys (ACS), and Cosmic Origins Spectrograph (COS).
Among these, WFPC2 is the main measurement device of the Hubble Space Telescope and plays a key role in high-resolution imaging of space celestial objects and phenomena. The device consists of four charge-coupled device (CCD) cameras, each optimized for a specific observation purpose. Three of these are ‘Wide Field’ cameras, which are used to capture wide areas such as galaxies, star clusters, and large-scale cosmic structures. These cameras provide a wide field of view, which is important for understanding the structure and interactions of large-scale celestial bodies. On the other hand, the remaining one, the ‘Planetary Camera’, is designed with a narrower field of view and higher resolution, making it suitable for observing the detailed characteristics of planets, stars, and other small celestial bodies. WFPC2 is equipped with a filter system that can separate and observe light of various wavelengths, making it essential for analyzing the chemical composition and physical state of celestial bodies. This advanced configuration of WFPC2, which enables the observation of star formation and evolution, interactions between galaxies, and various celestial phenomena with a deeper and wider view, is making a broad contribution to astronomical research.
▲ Outer space taken with WFPC2 (Caldwell 103). Source: NASA
CCD cameras use advanced technology to convert light into electrical signals to form images. When light reaches the surface of the CCD chip, each pixel converts the energy of the light into electrons by the photoelectric effect, and the number of electrons generated in each pixel is proportional to the intensity of light. These electrons move sequentially and are converted into analog signals and finally into digital image data. The high-resolution images obtained through this process enable detailed capture of various objects in the universe, such as stars, planets, and galaxies.
WFPC2’s CCD camera is used in combination with an advanced filter system, which selectively allows light of a specific wavelength to pass through. For example, red, green, and blue filters each allow only light of that color to pass through and block light of other colors. The monochrome images obtained through this filtering are later combined to form a full-color image. The image obtained through each color filter represents the intensity of light of that color, and through the synthesis of this information, objects in the universe are reproduced in close to natural colors.
Additionally, a polarizing filter was applied to WFPC2. This filter is a filter that has the function of detecting the ‘polarization state’, that is, the electric field of light oscillating in a specific direction. Light exists in the form of electromagnetic waves, and the electric field of these electromagnetic waves can oscillate in various directions. Generally, light vibrates in many directions, but using a polarizing filter, only light that vibrates in a specific direction can be passed through or blocked. It is used to analyze the characteristic patterns that occur when light interacts with various materials. This filter plays a key role in high-resolution imaging of space objects and phenomena. WFPC2’s polarizing filter detects and analyzes polarized light generated by interactions with dust, gas, and other substances surrounding celestial objects. This allows astronomers to obtain important information such as the magnetic field of a celestial body and the structure and composition of materials. In particular, it plays an important role in the study of star formation zones, galactic magnetic fields, and planetary atmospheres.
▲ Wide-field image of NGC 7635 taken by the Hubble Space Telescope. Source: Wikipedia
WFPC2, the wide-field camera of the Hubble Space Telescope, is the result of the physical effects of the photoelectric effect and polarization state. The photoelectric effect implements the intensity of an electric signal that changes depending on the intensity of light through a semiconductor, and the polarization state is implemented by a filter that separates specific light. Through these two core technologies, we can visually experience the mysterious scenes of the universe. Generally, the universe seen by our eyes is just a mixture of twinkling starlight in the black night sky, but through a wide-field camera such as the Hubble Space Telescope’s WFPC2, we can look into various aspects of the universe hidden in the darkness and starlight. It came to be.
Youngdu Lee, Ph.D. in Engineering
[ⓒ 울산저널i. 무단전재-재배포 금지]
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