Star hopping: finding things without a computer

A telescope shows a very small piece of sky. A typical eyepiece view is around half a degree to one degree across — roughly the width of the full Moon — against a sky that is 360 degrees around. Pointing it at something you cannot see with your eyes, by aiming down the tube, is close to hopeless, and discovering that on the first clear night is what ends a great many beginnings.

Star hopping solves it by never asking you to aim at the target. You aim at something you *can* see, and then move in short, known steps to something you cannot.

What you need

A working finder, a chart, and a low-power eyepiece

What you do not need

Motors, alignment, or a phone

The first thing to fix

Finder alignment, in daylightAlmost every beginner failure is a misaligned finder.

Time to learn

One evening, then it is permanent

This is the step people skip and it is the reason most of them fail. A finder that points somewhere slightly different from the main tube makes every hop wrong, and in the dark you cannot tell that is what is happening.

1. 1

   Step 1: Point the telescope at something distant and fixed, in daylight

   A chimney, a pylon, a church spire — at least a few hundred metres away. Never the Sun.

   You will know it worked when: A target that will not move while you work.

2. 2

   Step 2: Centre it in the main telescope at low power

   Use the longest focal length eyepiece you have, which gives the widest field and the easiest job.

   You will know it worked when: The main tube is aimed at a known point.

3. 3

   Step 3: Adjust the finder until it agrees

   Without moving the telescope, turn the finder’s adjustment screws until the same object sits on its crosshair or dot.

   You will know it worked when: Finder and telescope now point at the same place.

4. 4

   Step 4: Check it again at the start of every session

   It drifts, particularly if the telescope travels in a car.

   You will know it worked when: Every subsequent hop starts from the truth.

The method is to build a chain of stars from one you can see with your eyes to the object you want, where each step is short enough to be inside the finder’s field of view. A typical finder shows five to six degrees, so each hop is a few degrees at most.

The single most useful preparation is knowing how big your own fields of view are. Point the telescope at a known pair of stars whose separation you can look up, and see how they sit in the finder and in the eyepiece. From then on the chart has a scale you can feel.

Working from chart to eyepiece:

1. 1

   Step 1: Find the naked-eye anchor

   A bright star or a recognisable pattern near the target. This is the only part that needs a dark-adapted eye rather than a chart.

   You will know it worked when: You are pointed roughly in the right region.

2. 2

   Step 2: Plan the route on the chart before touching the telescope

   Pick two or three intermediate stars forming a shape you will recognise — a triangle, a curve, a pair of similar brightness. Shapes are far easier to re-find than single stars.

   You will know it worked when: You know what you are looking for before you look.

3. 3

   Step 3: Move one hop at a time in the finder

   Move until the next pattern is centred. Do not try to jump the whole distance.

   You will know it worked when: Every step is verifiable, so a mistake costs one hop rather than the attempt.

4. 4

   Step 4: Switch to the eyepiece at the lowest power you have

   Wide field first, always. Magnify only once the object is centred.

   You will know it worked when: The largest possible target area for the final step.

5. 5

   Step 5: Use averted vision on faint targets

   Look slightly to one side of where the object should be. The edge of the retina is considerably more sensitive than the centre, and many faint objects appear only this way.

   You will know it worked when: Objects that seemed absent become visible.