What is Optical Astronomy?
This branch of astronomy utilises the optical wavelengths, which, broadly speaking, range from about 300 nano-metres (nm, 10-9 metres) to 1000nm. It also is the oldest observing regime in astronomy, since the original detector used for observations was the human eye.
Generally, the eye is sensitive from about 400nm to 700nm or so, but with the addition of detector hardware such as photographic emulsions, photo-multiplier tubes and solid-state detectors such as CCD cameras, the range has been extended to include some of the near ultra-violet and the near infra-red.
This range of wavelengths is one to which the Earth's atmosphere is transparent, to a greater or lesser degree, so ground-based telescopes can cover the full range of these wavelengths.
How Do We Make Observations?
A low-resolution spectral image of Eta Carinae, taken from campus. Wavelength increases from left to right. The bright dots are emission lines in the star's spectrum.
As the technology available to optical astronomers has advanced over the centuries, we have come to perhaps three main data-gathering methods:
- imaging, where we want to see what an object or part of the sky looks like;
- photometry, where we want to measure the brightness of an object; and
- spectroscopy, where we study the elemental composition of objects, and other parameters such as their motion relative to the Earth.
A phase plot (brightness vs. orbital phase) of the eclipsing cataclysmic binary system V895 Cen. Data from 1996-2008, including one night in 2005 when the system was in an unusually bright state; this system shows significant changes in behaviour over time.
An optical telescope is used both to form a detailed image of an astronomical object and also, very importantly, to collect more light (i.e. more photons) from that source. This second point means that we can make more accurate measurements of that light, and thus determine the properties of that source more accurately and precisely.
A detector (most commonly an electronic detector such as a CCD camera) is placed at or near the telescope focus and, depending on the observations being made, it could be preceded by a spectrograph (for spectroscopic observations) or a filter (in order to restrict the observations to a particular smaller range of wavelengths).
Whilst the majority of observations are done from the Earth's surface, space-based facilities such as Hubble and Kepler take advantage of being above the Earth's atmosphere, obtaining data that can not be obtained from the ground.
What We Do in HEAG
Most of our optical work is done with a telescope on campus (see the Observatory section for more information). Although in a light-polluted and low-elevation environment, this facility nonetheless obtains data of scientific use.
Most research work is in the areas of cataclysmic variable star photometry, and exoplanet transit photometry. As this is a small facility operated solely by HEAG, there are no restrictions on availability, and we can dedicate the system to whatever observing programmes we wish. These observing programmes can be part of international campaigns for observing or monitoring particular sources, such as exoplanet host stars.
For more information, please contact Dr. Padric McGee.