HINTS ON OBSERVING

This article featured in the December 2003 Beginners Magazine

GETTING STARTED

In the October magazine we started a series of articles on observing techniques and expectations from your equipment. The beginner to astronomy is unlikely to have a large telescope and may have no equipment at all. This does not mean that observations cannot be carried out. The October article gave advice on purchasing and using binoculars that would be the first step towards buying equipment. A star chart and preferably a pair of binoculars if they are available is the only equipment that is necessary, to get started.

The next prerequisite is a clear night. Unfortunately these are usually best in the winter so warm clothing is essential. Make sure you start with warm clothes on because once the cold has taken hold, it is very hard to warm up, even when extra clothes are put on. A small torch is needed to enable the chart to be read but this must only shine with a dimmed light. A cycle, rear light or fit a piece of red plastic secured over a torch will give enough light but will not spoil ‘night vision'. It takes about 20 – 30 minutes for our eyes to become fully adjusted to the dark but a flash of bright light will spoil night vision in a second. If the torch is still too bright fix a piece of cardboard with a hole in it over the lens as well as the red screen to reduce the light.

Next find a dark area away from any lights. This may be difficult due to street lights but a strategically positioned screen made from a blanket or towel may help. If all fails go out of town to a dark field or hill. If you are lucky enough to have an area in the garden that is sheltered from lights a few comforts can be indulged. The first and most important would be a reclining chair to prevent neck ache from looking up for too long. A garden lounger chair is ideal for this purpose. A small table and an old quilt can add extra warmth and comfort.

Now down to serious observing. Allow at least 5 minutes for your eyes to become accustomed to the dark. This time can be used for setting up and getting comfortable. Get all of your equipment out first then turn any lights off than you can set up using torch light. Unless you are looking for something specific, position the chair so it is facing south but this is not essential. Have a look around the sky and pick out the brighter stars and see if any form what appear to be associated groups or patterns. Next get the star chart ready for use. If you do not have a chart the ones included on this website will do.

Star charts have to be orientated according to the time of year so that it can be aligned to the sky on the night it is being used. The stars appear to slightly change their position from night to night. This is because Earth is moving around the Sun on its orbit. Earth takes 365¼ days (a year) to complete one orbit of the Sun. A circle (the approximate path of Earth's orbit) is normally divided into 360 degrees therefore we could say that the Earth moves approximately 1 degree around the Sun per day. This means that viewed from Earth, the sky appears to move approximately 1 degree from east to west every day. Put another way in 30 days (a month) the sky appears to move 30 degrees.

From one night to the next the change in position of the stars will not be noticeable but a month will make a significant difference. The charts in the 'Whats Up' section of this site are drawn so that south is at the bottom of the chart in the middle of this month. There is however an added complication caused by the rotation of Earth. Earth rotates once every 24 hours (1 day). Again we can say one rotation is 360 degrees so the sky appears to move 30 degrees per hour due to Earth's rotation. The charts show the sky at 9 o'clock on 15 th of the month. At 8 o'clock the sky will appear 30 degrees further east and 10 o'clock 30 degrees further west.

So now we need to start finding our way around the sky. The conventional method is to use constellation recognition. First we might ask, what are constellations ? Those bright stars we looked for earlier, that appear to form patterns in the sky, are the constellations. The charts show the internationally accepted constellations of which there are 88 covering the whole sky. The charts show the brightest stars joined by lines to denote the grouping for each constellation. The constellations of the northern hemisphere, are named after characters from mythology and mostly originate from ancient times.

Very few constellations look like the character they are named after. Cygnus the Swan, Leo the Lion and Orion the Hunter are perhaps the exception and do, with a little imagination, look remotely like those characters. The stars making up the constellations are not generally physically associated and are simply formed by a ‘line of sight' effect.

The constellations are used, somewhat like the county boundaries on a map of the British Isles. The boundaries of the constellations are shown in yellow on the chart. The brighter stars within the boundaries are like the main towns on a map and the fainter stars the small towns and villages. The analogy continues with the identification of the stars within the constellation. On a map we would say Reading in Berkshire, on a star chart we would say Vega in Lyra or Rigel in Orion. We can therefore find objects in a constellation be saying, that object is a certain distance from a star in a particular direction. We will however have to be able to locate and recognise the constellation patterns.

There are a number of constellations that are easier to recognise, amongst these are : Ursa Major (The Great Bear or The Plough), Orion (The Hunter) and Cassiopeia (appearing like a ‘W'). Most people will be able to identify these. Once one of these has been identified other constellations surrounding it can be found. Gradually by using the chart, other constellations can be identified by working out from the known one. Ursa Major is probably the best to use to start your orientation because it is ‘circumpolar'. That means it visible all year and does not disappear below the horizon. The text below the charts on this site give advice on how to use Ursa Major to find Polaris the Pole Star and how to orient the chart for use. Almost directly opposite Polaris from Ursa Major and about the same distance away is the constellation of Cassiopeia. With its distinctive ‘W' shape it is a useful short cut for constellation identification.

It is now time to thinking about what there is to see in the night sky and what will be needed in the way of equipment to see it. The next article in this series is a supplementary article (also appearing in the December 2003 issue) about magnitudes. This is the means that astronomers use to estimate the brightness on an object. The naked eye is capable of seeing objects as faint as magnitude 6 on a very clear night and at a very dark location. In the Thames valley magnitude 4 is usually the limit due to mist and light pollution. A pair of binoculars will at least double this magnitude limit and bring much fainter objects into view.

On a clear night it is possible, even from the Newbury area, to see the Milky Way. This is a misty band crossing the sky from horizon to horizon. It is best seen directly overhead running through the constellations of Cassiopeia, Cygnus (in the summer) and Auriga (in the winter). It is in fact the galaxy in which our Sun is located. Our Sun is one of 200 billion stars in the Milky Way. Next we will consider observing stars and groups of stars.

 

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