What Is A Diffraction Spike

What is a Diffraction Spike?

You must have come across the bright crosses in a dark sky at least once. It must have made you wonder- is that even legit.

Yes, it is a real phenomenon – the diffraction spike. You’d be surprised that these patterns are a manifestation of your telescope.

We will get through more light on these blingy patterns in this section. Follow along for an exciting voyage of astronomical endeavours.

What are diffraction spikes?

Diffraction spikes are a direct effect of telescopic observations. If your telescope has a larger primary mirror, you must be very well-versed with these patterns.

Diffraction spike caused by support rods

When the primary mirror directs the incoming light rays onto a secondary mirror. It can also be a sensor instead of a secondary mirror where the light is falling.

The sensor is staged on top of the primary mirror. The telescope’s secondary mirror then directs the light out.

In the second case, the sensor is responsible for image conversion. The conversion results in an electrical signal.  This signal is then conveyed to an attached computer.

We stress on the placement of the secondary mirror or the sensor here. For this phenomenon to occur, these two integrations should be held atop the primary mirror.

The support rods use for holding the sensor or the secondary mirror in place are called vanes or struts. The light from the stars entering the telescope is of interest to us.

This light enters the telescope in the direction of the primary mirror. It avoids the supporting rods, undergoing deflection.

The supporting rods are the obstruction here. This obstruction in the way of the incoming starlight is what forms the spike diffractions.

The final images show a shifting placement of these spikes. This can also be attributed to the obstruction is the starlight’s path.

For luminous celestial objects such as stars, the shifting patterns form as a radical spike. If the support rods are aligned geometrically, the diffraction spikes are also formed geometrically.

These spikes are incredibly bright for highly luminous stars. But fainter stars, they are not as apparent.

Diffraction spikes are purely caused by the presence of support rods in a telescope. If these supports are absent, there is no diffraction.

Diffraction spikes caused due to aperture

An aperture’s edge is also responsible for causing diffraction spikes. The aperture is the gateway that lets in the light from these stars.

The aperture’s entrance is sharp from where the light passes. This sharp edge is what causes the diffraction.

Most apertures in telescopes are typically circular. The diffraction is hence, in the form of circular rings.

These diffraction rings are quite dim. They can also cause a slight blur in the final image. There are several optical pieces of equipment that make these rings seem more apparent.

If the rings seem asymmetrical or non-circular, they are undoubtedly caused by your telescope’s aperture. A camera’s diaphragm can better witness this phenomenon.

A camera’s diaphragm allows you to adjust the aperture’s size. These diaphragms are responsible for creating diffractions that are generally polygonal.

Creating your diffraction spikes

If you have seen diffraction spikes before, you know there are beautiful. Most photographers intentionally create these spikes in astronomical images.

Creating intentional diffraction spikes is straightforward. You need a bit of deduction to get it right.

What do you need to create diffraction spikes?

You will need a small piece of wire. The wire should be around 2 mm thick. You can use an A string of your guitar if you have one.

You will also need thin cardboard, duct tape, pliers, and scissors. By the end of the next section, you will have all the steps that you need to make your imaging more blingy.

Steps for creating diffraction spikes

1. Begin by cutting the cardboard into thin strips. The strip should be at least 3 cm longer than the objective of your telescope.

2. Curl the cardboard strop around the telescope’s objective. Secure the ends with the help of duct tape.

3. Now cut the string or the wire into a two-piece. Each piece should be 6cm more in length than your telescope’s objective.

4. Attach one end of the wire to the cardboard strip that you just attached to the end of the objective. Curve the wire along the length of the telescope’s objective.

Make sure that the wire is straight and properly aligned. Secure the wire on either side of the carboard with duct tape.

5. You have successfully made the setup. Now, you are ready to click some blingy Astro images.

Recommended Reading:


  1. Photographing Space
  2. lpl.arizona.edu
  3. Sky at Night Magazine
  4. WTAMU