Telescopic meteor observing

Although long regarded as a less popular way of watching meteors, telescopic results are of much greater accuracythan those obtained by naked-eye meteor plotting. This greater accuracy makes it easier to tie down the locations of meteor shower radiants.

In recent years, however, video observing has greatly increased our knowledge of naked-eye meteor shower activity and this has further reduced the enthusiasm for telescopic observing.

Telescopic observing can still have value for fainter meteors. Indeed, whereas some meteor showers, such as the Perseids and Geminids, are rich in bright meteors and deficient in fainter meteors, there are others, such as the southern Delta Aquarids and Giacobinids, that are more active below naked-eye magnitudes. Radar observations, which also predominantly detect the smaller particles that produce faint meteors, can monitor small particle rates to some extent, but the relationship between radar, telescopic and naked-eye rates of meteor showers is not yet fully understood. There have been a number of cases in recent years in which reported high radar rates do not seem to have coincided with enhanced naked-eye rates.

The major item of equipment needed is a small telescope or a pair of binoculars (7x50s or 10x50s are ideal) which should be firmly mounted on a tripod or other suitable stand so as to allow you to follow your selected field of view in comfort and with ease. In choosing the instrument, it is important to remember that larger apertures and higher magnifications mean that you will be looking at a smaller area of sky, which will reduce the number of meteors seen.

Each field is best centred about 25° to 30° from the known or suspected shower radiant under examination, and around 35° to 65° from the horizon. Pairs of fields need to be observed at different angles to this radiant, to allow the radiant to be defined during an observing session. Alternate between the fields at about 20-30 minute intervals, with a 5-minute break or so in between. Make sure both fields can be observed comfortably using your equipment.

Observing notes should include the date, watch times and durations, your name and site location as usual, along with the type of equipment employed, the size of its primary lens or mirror (depending on whether it is a refractor or reflector respectively), the magnification used and the field diameter in degrees. This latter item can be worked out (if not already known) following the method in “Norton’s 2000.0”, page 72, or any good general astronomy text.

Once decided upon, each field centre’s co-ordinates in R.A. and Declination must be recorded and the field stars need to be drawn on to a pre-prepared circle of about 8 cm diameter. Also write down the field limiting magnitude.

During the watch, positions for all meteors seen are to be plotted onto your star-field sketch. When a meteor appears, “freeze” your attention on it until you are certain of the path details, and then copy the track down. A 15 cm ruler is useful for this purpose. Mark the line with an arrow to show the meteor’s direction of motion, and assign each meteor a letter, which is then keyed to a written description. This description should include the letters “a” or “o” for each end of the trail (“a” = inside the field, “o” = outside it; e.g. “aa” means a meteor completely in the field of view, “oa” one which ended in the field having started outside), how bright it was compared to the field stars, its speed, any colour or train. A sample telescopic meteor plot is given nearby.

telescopic meteors

Rates should be similar to normal visual ones, as many fainter meteors become visible to compensate for the restricted field of view, and most showers exhibit some telescopic activity.