Can we look through the telescope?

The JGT does not have an eyepiece to look through. Astronomers really only look through telescopes for fun. Professional telescopes are more like a camera that you hold up to take a picture. Cameras have two advantages over the human eye. First, the pictures can be recorded, analysed, and shared with people all over the world. And second, while the light really only sees this instant, the camera can collect light over minutes or hours and so see fainter objects or deeper into the Universe. Our smaller telescopes generally have eyepieces to look through.

What was the most exciting thing the JGT has discovered?

This question has many answers. Every observer probably has a different story to tell. Some of the most exciting observations of the past years have been our co-discoveries of exoplanet transits with the JGT. Other exciting observations include highly variable stars, like supernovae or young stars undergoing an accretion outburst. Or what about the eclipse of a star by Neptune’s moon Triton, an event that only took a couple of minutes?

How far can we look with this telescope?

That depends how bright the thing is you are interested in. Astronomers are interested in very luminous objects that are very far away (for example, a quasar or a supernova) or in very faint objects that are nearby (for example, a brown dwarf or an exoplanet or an asteroid). Or something in between, obviously. With the JGT we have observed objects that are millions of lightyears away, but it is equally challenging to chase faint objects in the solar neighbourhood or tiny pieces of debris just outside the Earth’s atmosphere.

What is the magnification of the telescope?

Magnification is not a number that astronomers are very interested in. A star is what we call a point source, which means it does not appear bigger when seen through a telescope. The ‘size’ of a star in an astronomical image taken with our big telescope is determined by the so-called seeing. On its way through the atmosphere, the light is scattered many times, which turns the point source into a bright blob. The seeing in St Andrews is usually three arcseconds (i.e. a 1000th part of a degree). A number that is much more important for us is the sensitivity – how faint can a star be and still be detected in our images? This is primarily determined by the area of the light-collecting optics (i.e. the lens or the mirror). Therefore, the most important number when talking about a telescope is the diameter of the aperture.

How many clear nights do we get in St Andrews?

At the James Gregory Telescope, we can observe in about 50 and 80 clear nights every year. With ‘clear’ we mean that we get at least a few hours of stars. This excludes the summer months when the nights are too short for most of our science projects. Because all our observers are volunteers and usually have other jobs in the morning, we often miss clear sky in the second half of the night. So, conservatively, a dedicated observer in St Andrews could probably get about 100 clear nights per year, with a few hours of useful sky per night.