Telescopic Observations

Please note that telescopic observations are virtually nonexistent nowadays. Some of the content in this section is outdated.

When to organize an observation

Telescopic observation is less tied to the major showers than other techniques, and so any clear, dark night is fine. By observing when there is no major shower, there is a greater chance of finding the unexpected shower, simply because far fewer observations have been made. This is especially true for the mornings in the first half of the calendar year.

That said, new observers might ‘learn the ropes’ by commencing during a period of greater activity, say September, when the sporadics are most numerous, or during the Geminids when several showers combine to give double normal rates. As a novices you are more likely to try again if you’ve seen meteors, but not otherwise. It still has to be fun. Seeing a reasonable number of meteors is important to gain sufficient practice of memorizing, recording, and plotting data, and to become familiar with the general appearance of telescopic meteors. It is not the same as visually, since the angular speed is magnified too. Most telescopic meteors come and go in a fraction of a second. The observer does need to hone good reactions.

Telescopic watching does take quite a bit of getting used to and observers should persevere. Experience is gained rapidly, and the hourly bag of meteors will climb steadily.

Telescopic rates are very sensitive to sky conditions. That’s because the narrower field of view means that the average apparent magnitude is dimmed compared with the visual observer. Given a choice avoid twilight and when the Moon is prominent (say between first and last quarter phases). Extinction of a rising or setting moon by the atmosphere can extend an observing session by up to 30 minutes. There are sometimes special or ephemeral events which justify diverging from these recommendations, like a possible shower outburst. It is sometimes possible to observe through broken cloud, when the visual observer would stop.

Sporadic activity increases from dusk to dawn, so a later watch is likely to yield more meteors.

Where to hold an observation

As indicated earlier, sources of illumination reduces the number of meteors seen. If you are bored from a low rate, you might miss a meteor or record its parameters inaccurately. Therefore finding a dark site free or with minimal artificial light is crucial to a successful watch.

That’s easier said than done given that most people live in cities and today’s preponderance of light trespass from unshielded security and street lamps. Increased particulates in the air also reflect artificial lighting. Eyes can be shielded from direct illumination which would otherwise ruin dark adaption. A coat hood, a dark cloth, rubber caps for eyepieces do alleviate the situation. Sometimes talking to your neighbours and explaining what you do, you can get them to switch off the security lighting and pull curtains when you are observing.

While some are lucky and can observe their backyard or garden, finding a dark site often involves some travelling to the countryside and away from main roads. This is a hassle, especially with a telescope and chair, but if you intend to watch for an extended period, it reaps dividends. You obviously have to weigh up the time to travel versus how long you intend to observe. If you do travel, have a check list of things to take. There’s nothing worse than driving a long way and found that you have forgetten your observing chair. Going with an observing partner helps pass the journey time, and is safer.

Necessary materials

A crucial factor determining whether or not you will see telescopic meteors is your comfort. This cannot be overstressed. If you are cold or contorting to reach the eyepiece, you will not be giving your undivided attention to meteors. Your observed rate will plummit.

Spend time devising a setup where you can observe without strain. This may involve making or buying a binocular mount, or finding a second-hand typists chair with adjustable seat height.

Many telescopic observers are sitting upright rather than laying on a lawn chair, so it’s easier to become exposed to the elements. Wind chill becomes a more important factor.

Comfort is essential for good observations. Cold and damp nights are at best unpleasant for the unprotected observer, and at worse can be very dangerous if prolonged exposure to conditions like these occurs. Ordinary things can help here. You might find the following useful:

  • a deck chair, garden lounger, or camp bed with your instrument, especially binoculars; or where you look down, say with a refractor and star diagonal, an adjustable height observer’s chair, or even a small office chair;
  • a sleeping bag or blanket (even in summer);
  • warm clothes — not tight-fitting ones, many thin layers are better than a few thick ones as the air trapped between the layers is a good insulator;
  • pillows to incline the observer’s head if lying on a camp bed;
  • a cover to keep the dew and/or frost off bedding and equipment
  • food and drinks to consume during observing breaks; do not have hot drinks — they can dilate the blood vessels and make you feel colder once the short-term warming of the drink disappears.

The actual observing equipment consists of:

  • mounted binocular or telescope;
  • an accurately set watch (ideally a digital one or a radio-calibrated watch which is kept precise by a long-wave broadcasting signal);
  • a wide clip board (at least A4 sized) so that the report sheet and charts may be placed side-by side;
  • a dim red torch (and spare) — an adjustable LED reader’s light that clips on to your board or tripod works well, spare batteries;
  • two pencils (at least) and an eraser;
  • two white 20-30cm ruler for plotting, white because it’s easier to find if you drop it (and you will);

The LED lights use little power so are more economical, and you are not forever changing batteries.

Preparations for the watch

Chart selection

Since the field of view is much narrower than using for visual observing, more careful planning of where to look is needed. This means you need to select the charts to take to the observing site.

Given a single radiant the aim is to select two fields such that meteors traced back would intersect at near right angles at the radiant. The distance from the radiant does depend on the speed of the shower’s meteors. This is mainly to optimise the numbers seen, since the apparent speed increases with radiant distance (up to 90 degrees) against the cross section of atmosphere being monitored. Another issue is that the plotting accuracy at the radiant largely depends of the orientation error of the plotted meteor’s path multiplied by the radiant distance. So telescopic observers tend to view closer to the radiant than their visual counterparts.

For swift meteors like the Leonids and Perseids 10-20 degrees is recommended. For medium speed like the Geminids, 15-30 degrees is satisfactory. For slow meteors such as the Piscids, the fields can be 25-40 degrees away.

When selecting fields to observe, another factor is have fields which are fairly easy to locate, i.e. contains stars easily visible to the naked eye; and have a good mix of star brightnesses for estimating meteor magnitudes.

Multiple radiants such as the Aquarid-Capricornid complex in July and August need more fields to discriminate between the various sources, and possible occlusions (where in a given direction from your field there is more than one radiant). Merely choosing two fields can generate artifacts in the analysis of your observations. For studying the radiant structure of good telescopic showers, like the Geminids and Orionids, it’s best to have about 6 to 8 fields surrounding the radiant.

It is inevitable that some of the criteria have to be relaxed. To help you, IMO has produced sets of charts for specific showers, looking for minor showers, and monitoring sporadic activity. To assist you in the selection process IMO recommends certain charts for certain showers.

At your desk

Plot the actual radiant position(s) onto the star charts you will be using, taking into account the radiant drift which can be looked up in the Shower Calendar. Check the times of twilight, radiant elevation and moonrise/set and plan your watch according to these circumstances.

At your observing site

A good observer has a pair of vigilant eyes, as the fast and often faint meteors require quick reflexes and good perception. Lack of Vitamin-A as well as the side effects of alcohol and nicotine negatively affect visual perception. Smokers have to realize that their eyes will not dark adapt completely, even if they stop smoking for a while.

Regarding your dark adaption you should avoid blinding lights before setting off to observe and you should always:

  • use your red torch
  • allow plenty of time for your eyes to fully dark-adapt (at least 20 minutes from a well-lit room).

Carefully choose your observing direction:

  • It should not be covered by trees, etc., or illuminated by artificial lights or the Moon.
  • The center of the field of view should be at 50° to 70° elevation.
  • Do not look directly at the radiant. A distance of between 20° to 40° away is optimal. Report the center of the field in your notes.

Then arrange your equipment according to the direction chosen. If you use a tape recorder, test whether it is working correctly, otherwise you will lose all your data. You will also need to be familiar with its use in complete darkness. Before you start to observe spend some minutes in memorizing:

  • the radiant position you plotted onto the chart,
  • the magnitude of several stars within your field of view for comparison with the meteors (magnitudes are indicated on the charts),
  • the fields for determining the limiting magnitude.

The observation

The observation goes entirely the same as for a visual observation. Please follow the instructions as outlined there for your telescopic observations as well.