Irish Astronomy


Optics in astronomy involves the study of light and its behavior as it interacts with lenses, mirrors, and other optical components in telescopes and instruments. Understanding optics is crucial for achieving clear and detailed views of celestial objects.

Find answers to FAQs about optical principles, telescope optics, and choosing the right equipment for astronomical observations.

Optics FAQ

  • telescopes
    • Which telescope is recommended for deep-sky astrophotography?

      For deep-sky astrophotography, telescopes with large apertures and wide fields of view are preferred to capture faint and expansive celestial objects like galaxies, nebulae, and star clusters. Schmidt-Cassegrain telescopes (SCTs) and refractors with apochromatic lenses are popular choices for their versatility, compactness, and image quality. Equatorial mounts with accurate tracking capabilities are essential for long-exposure imaging, allowing for precise tracking of celestial objects to prevent motion blur and trailing. Additionally, accessories like autoguiders, field flatteners, and coma correctors enhance imaging performance and results.

    • What telescope is best for beginners?

      The best telescope for beginners depends on factors like budget, interests, and observing preferences. Generally, Dobsonian telescopes are recommended for their simplicity, affordability, and large apertures, providing excellent views of the Moon, planets, and deep-sky objects. Refractor telescopes are also popular for beginners due to their low maintenance and high-quality views, while computerized (GoTo) telescopes offer guided tours of the night sky, aiding in learning and exploration. Ultimately, the best telescope is one that aligns with the beginner’s goals and encourages enjoyable and rewarding stargazing experiences.

    • What is the significance of the James Webb Space Telescope?

      The James Webb Space Telescope (JWST) is a next-generation space observatory developed by NASA, ESA, and CSA, scheduled for launch in the near future. It’s designed to study the universe in infrared wavelengths, offering unprecedented sensitivity and resolution for observing distant galaxies, star formation regions, exoplanets, and the early universe. JWST aims to address fundamental questions about the origins of galaxies, stars, and planetary systems, shedding light on cosmic history and the potential for life beyond Earth. Its launch represents a significant milestone in astrophysics and space exploration.

    • What is the Hubble Space Telescope?

      The Hubble Space Telescope (HST) is a space-based observatory launched by NASA in 1990, named after astronomer Edwin Hubble. It orbits Earth above the distorting effects of the atmosphere, providing high-resolution images and data across a wide range of wavelengths, from ultraviolet to near-infrared. Hubble has revolutionized our understanding of the universe, contributing to discoveries in cosmology, galactic evolution, stellar astronomy, and planetary science. It remains one of the most iconic and productive scientific instruments in the history of astronomy.

    • What is the difference between aperture and magnification?

      Aperture refers to the diameter of the primary optical element (e.g., lens or mirror) in a telescope, determining its light-gathering ability and resolving power. Magnification, on the other hand, is the degree to which a telescope enlarges the apparent size of viewed objects and details, calculated by dividing the focal length of the telescope by the focal length of the eyepiece. While aperture determines a telescope’s ability to collect light and resolve fine details, magnification affects the apparent size and clarity of observed objects, with higher magnifications often requiring larger apertures for optimal performance.

    • What is the difference between an equatorial and an altazimuth mount?

      An equatorial mount is aligned with Earth’s rotational axis and equipped with right ascension (RA) and declination (Dec) axes, allowing for easy tracking of celestial objects using coordinates that compensate for Earth’s rotation. In contrast, an altazimuth mount moves vertically (altitude) and horizontally (azimuth) and is simpler to operate but requires manual adjustments to track celestial objects accurately. Equatorial mounts are preferred for astrophotography and long-duration observations, while altazimuth mounts are popular for casual stargazing and terrestrial viewing.

    • What is the difference between a refracting and reflecting telescope?

      The main difference between a refracting and reflecting telescope lies in their optical design and light-gathering elements. A refracting telescope uses lenses to gather and focus light, whereas a reflecting telescope employs mirrors to capture and reflect light to a focus point. Refractors offer crisp, high-contrast views with minimal maintenance, while reflectors provide larger apertures at lower costs, making them ideal for deep-sky observation and astrophotography. Both types have their advantages and are suited for different observing preferences and applications.

    • What is the difference between a coma corrector and a field flattener?

      A coma corrector is an optical device used in reflector telescopes to reduce or eliminate coma aberration, a distortion that causes stars near the edges of the field of view to appear elongated or comet-like. It typically consists of lenses or corrective optics placed in the telescope’s optical path, improving image sharpness and clarity across the entire field of view. A field flattener, on the other hand, corrects field curvature and astigmatism, ensuring sharp focus and uniform illumination of the image field, particularly in refractor telescopes and astrographs. Both accessories are valuable for astrophotography, depending on the telescope’s optical design and imaging requirements.

    • What is the "exit pupil," and how does it relate to eyepiece selection?

      The exit pupil is the diameter of the beam of light exiting the eyepiece of a telescope and entering the observer’s eye. It determines the brightness and resolution of the viewed image, with larger exit pupils providing brighter but potentially lower-resolution views, and smaller exit pupils offering higher resolution but dimmer images. Selecting an eyepiece with an exit pupil matching the observer’s pupil size optimizes light transmission and viewing comfort, enhancing the observing experience, especially under varying lighting conditions and magnifications.

    • What is radio astronomy?

      Radio astronomy is a branch of astronomy that studies celestial objects and phenomena by detecting and analyzing radio waves emitted or reflected by astronomical sources. It allows astronomers to explore the universe beyond the visible spectrum, revealing insights into cosmic processes like star formation, galaxy evolution, and the presence of interstellar matter and magnetic fields. Radio telescopes and interferometers are used to collect and analyze radio signals from various regions of the sky.

    • What is chromatic aberration?

      Chromatic aberration is a type of distortion that occurs when a lens fails to focus all colors to the same convergence point, resulting in fringes of color appearing around objects, particularly at the edges of the field of view. It’s common in refracting telescopes due to the dispersion of light through different wavelengths.

    • What is a star tracker buyer's guide?

      A star tracker buyer’s guide provides information and recommendations for selecting a star tracker, a portable tracking mount used for astrophotography. It typically includes factors to consider when choosing a star tracker, such as payload capacity, tracking accuracy, compatibility with camera equipment, and budget. Additionally, it may feature reviews, comparisons, and tips for optimizing performance and usability of star trackers for capturing long-exposure images of celestial objects.

    • What is a star diagonal, and do I need one?

      A star diagonal is an accessory used in telescopes to angle the eyepiece for comfortable viewing, especially when observing objects high in the sky. It contains a prism or mirror that reflects light at a 90-degree angle, allowing observers to view celestial objects without straining their necks or contorting their bodies. While not essential, a star diagonal improves viewing ergonomics and is recommended for prolonged observing sessions, particularly with refractor and catadioptric telescopes.

    • What is a refractor telescope?

      A refractor telescope is an optical instrument that uses lenses to gather and focus light, producing images of distant objects. It consists of an objective lens at the front that collects light and forms an image, and an eyepiece at the back that magnifies and projects the image for viewing. Refractors are known for their crisp, high-contrast views, making them popular for observing the Moon, planets, and terrestrial objects. They’re relatively low-maintenance and well-suited for beginners and visual observers.

    • What is a power supply for telescopes?

      A power supply provides electrical energy to operate motorized components and electronic accessories in telescopes, such as GoTo systems, tracking mounts, and dew heaters. Depending on the telescope’s design and power requirements, power can be supplied through batteries (e.g., rechargeable or disposable), AC adapters, or portable power packs. Choosing the right power supply ensures uninterrupted observing sessions and reliable performance of telescope equipment.

    • What is a Dobsonian telescope? Why is it recommended for beginners?

      A Dobsonian telescope is a type of Newtonian reflector telescope mounted on a simple yet stable altazimuth mount. It’s recommended for beginners due to its ease of use, affordability, and large aperture, which provides excellent views of celestial objects. Dobsonians are known for their simplicity and are ideal for visual observing, particularly deep-sky objects.

    • What is "seeing," and how does it affect telescope observations?

      “Seeing” refers to the stability and clarity of the Earth’s atmosphere, influencing the sharpness and detail of telescope observations. Factors like temperature variations, air turbulence, and atmospheric moisture can cause distortion and blurring of celestial images, affecting observing conditions. Poor seeing conditions result in diminished image quality, particularly at high magnifications, while steady seeing allows for clearer views and finer details. Monitoring weather forecasts and local seeing conditions can help astronomers plan observing sessions for optimal viewing experiences.

    • What are the differences between a star tracker and an equatorial mount?

      A star tracker is a portable tracking mount designed specifically for astrophotography, capable of accurately tracking the apparent motion of celestial objects across the sky. An equatorial mount, on the other hand, is a stationary or motorized mount aligned with Earth’s axis, allowing for manual or motorized tracking of celestial objects using right ascension (RA) and declination (Dec) coordinates. While both are used for imaging, star trackers are more compact, lightweight, and suitable for wide-field astrophotography, whereas equatorial mounts are versatile for various telescope setups and tracking needs.

    • What are some good resources or books for learning about astronomy equipment and usage?

      There are numerous resources and books available for learning about astronomy equipment and usage, catering to various skill levels and interests. Some recommended titles include “NightWatch: A Practical Guide to Viewing the Universe” by Terence Dickinson, “The Backyard Astronomer’s Guide” by Terence Dickinson and Alan Dyer, and “Turn Left at Orion” by Guy Consolmagno and Dan M. Davis. Online platforms, astronomy forums, and local astronomy clubs also offer valuable information, advice, and community support for amateur astronomers.

    • What are eyepieces?

      Eyepieces are optical components that magnify the image formed by a telescope’s objective lens or primary mirror. They come in various focal lengths and designs, affecting the magnification and field of view of the telescope. Choosing the right eyepiece is crucial for optimizing viewing experiences and observing different celestial objects.

    • What are "terrestrial" and "celestial" views in telescopes, and how do I switch between them?

      “Terrestrial” views refer to observing objects on Earth, such as landscapes, wildlife, or sporting events, using a telescope. “Celestial” views, on the other hand, involve observing celestial objects in the night sky, such as stars, planets, nebulae, and galaxies. To switch between terrestrial and celestial viewing modes, telescopes may require adjustments to focusing, eyepiece selection, and, in some cases, the orientation of optical components or accessories. Some telescopes come with flip mirrors or erecting prisms for easier transition between viewing modes.

    • How important is dark adaptation, and how long does it take?

      Dark adaptation is crucial for observing faint celestial objects and details in low-light conditions. It involves allowing the eyes to adjust to darkness, which can take anywhere from 20 to 30 minutes for significant improvement in sensitivity to dim light. Maintaining dark adaptation is essential during stargazing sessions, as exposure to bright lights can reset the process and hinder viewing capabilities. Using red light sources and avoiding unnecessary light pollution can help preserve dark adaptation.

    • How do I properly collimate a reflector telescope?

      Collimation is the process of aligning the optical components of a reflector telescope, such as the primary and secondary mirrors, to ensure optimal performance and image quality. It involves adjusting the tilt and position of the mirrors using collimation tools like a collimation cap or laser collimator. Proper collimation is crucial for sharp and accurate views, particularly at high magnifications, and should be performed regularly, especially after transportation or significant temperature changes.

    • How do I clean and maintain my telescope and its accessories?

      Cleaning and maintaining a telescope involve regular inspection, dusting, and occasional cleaning of optical surfaces with specialized tools and solutions. Proper storage, handling, and protection from environmental factors are also important. Accessories like eyepieces and filters should be handled with care and stored in a clean, dry environment when not in use. Following manufacturer guidelines and avoiding harsh chemicals or abrasive materials are essential for preserving optics and prolonging telescope lifespan.

    • How do I choose between a refractor and a reflector telescope?

      Choosing between a refractor and a reflector telescope depends on factors like budget, intended use, and personal preferences. Refractor telescopes use lenses to gather and focus light, offering crisp images and low maintenance, while reflector telescopes use mirrors, providing larger apertures at lower costs. Refractors are great for planetary viewing and beginners, while reflectors excel in deep-sky observation and astrophotography.

    • How do I align a computerized (GoTo) telescope?

      Aligning a computerized telescope involves selecting alignment stars and centering them in the telescope’s field of view. The telescope’s onboard computer uses this information to accurately determine its orientation and celestial coordinates. The exact alignment procedure varies depending on the telescope model, but typically involves following prompts on the telescope’s control panel or accompanying software.

    • Do I need a mount for my telescope? What types are there?

      Yes, a mount is essential for a telescope as it provides stability and allows for precise aiming. There are two main types: altazimuth mounts, which move in vertical (altitude) and horizontal (azimuth) axes, and equatorial mounts, which are aligned with the celestial poles and compensate for Earth’s rotation. Each type has its advantages and is suited for different purposes and preferences.

    • What is the ideal aperture size for astronomy binoculars?

      The ideal aperture size for astronomy binoculars is typically 50mm or larger. Larger apertures gather more light, allowing for better views of faint celestial objects such as galaxies, nebulae, and star clusters.

    • What is the difference between astronomy binoculars and regular binoculars?

      Astronomy binoculars typically have larger objective lenses, lower magnifications, and are designed with features optimized for stargazing, such as enhanced light-gathering capabilities, wider fields of view, and sometimes built-in filters for celestial observations.

    • What features should I look for in astronomy binoculars?

      Look for large objective lenses (50mm or more), moderate magnification (7x to 10x), fully multi-coated optics for maximum light transmission, and a sturdy, ergonomic design for comfortable prolonged use.

    • What are the best binoculars for astronomy?

      The best binoculars for astronomy are typically those with large objective lenses (50mm or more) and moderate magnification (7x to 10x). Brands like Celestron, Orion, and Nikon offer excellent options.

    • How do I properly collimate astronomy binoculars?

      Collimating astronomy binoculars involves aligning the optical components to ensure they work together correctly. Some binoculars have collimation screws that can be adjusted with a collimation tool, while others may need professional adjustment.

    • How do I choose the right magnification for astronomical binoculars?

      The right magnification for astronomical binoculars depends on personal preference and observing conditions. Generally, a magnification of 7x to 10x is recommended for stargazing to maintain a stable image and wide field of view.

    • How do I calculate the exit pupil of astronomy binoculars?

      The exit pupil of binoculars is calculated by dividing the aperture size (in millimeters) by the magnification. For example, 10×50 binoculars have an exit pupil of 5mm (50mm divided by 10). A larger exit pupil provides a brighter image, especially in low-light conditions.

    • Do I need waterproof or fog-proof binoculars for astronomy?

      Waterproof and fog-proof binoculars are highly recommended for astronomy, especially if you plan to observe in varying weather conditions or locations with temperature changes. They ensure durability and prevent internal fogging, maintaining clear views.

    • Can I use regular binoculars for stargazing?

      Regular binoculars can be used for stargazing, but astronomy-specific binoculars with larger apertures and lower magnifications are better suited for celestial observations due to their wider fields of view and better light-gathering capabilities.

    • Can I use binoculars to see planets?

      Binoculars can be used to observe some planets, such as Jupiter and Saturn, which appear as bright points of light with discernible features like Jupiter’s moons or Saturn’s rings. However, for detailed planetary observation, a telescope is recommended.

    • Can I use binoculars for stargazing, and what should I look for in a pair?

      Yes, binoculars are great for stargazing, offering a wide field of view. Look for ones with large objective lenses for better light-gathering capability and a wide field of view.

    • Can I use astronomy binoculars for daytime viewing?

      Astronomy binoculars can be used for daytime viewing, but their design and features are primarily optimized for low-light celestial observations. They may not perform as well as regular binoculars designed specifically for terrestrial use in bright daylight.

    • Are there specific brands known for producing high-quality astronomy binoculars?

      Yes, brands like Celestron, Orion, Nikon, and Canon are known for producing high-quality astronomy binoculars with excellent optics, durability, and features tailored for stargazing enthusiasts.

    • Are there any maintenance tips for keeping astronomy binoculars in good condition?

      To keep astronomy binoculars in good condition, store them in a protective case when not in use, avoid touching the lenses with fingers, clean lenses with a soft brush or lens cloth, and periodically check and adjust collimation if necessary for optimal performance.

    • Are there any accessories I need for astronomy binoculars?

      Accessories like a tripod adapter for mounting binoculars on a tripod, a padded carrying case for protection during transport, and lens cleaning supplies for maintenance are helpful additions to enhance your stargazing experience with binoculars.

    • Are image stabilization binoculars beneficial for astronomy?

      Image stabilization binoculars can be beneficial for astronomy, especially for high-magnification viewing where hand shake becomes more noticeable. They offer a steadier view, reducing image jitter and allowing for clearer observations.