Saturday, March 1, 2014

Sunspots

Sunspots are fascinating if you know how to watch and study them. Fortunately, you can observe and photograph sunspots safely with simple equipment and affordable accessories.
Here is a nice video

What are sunspots?
Sunspots are cooler areas on the sun surface. They are not really cool, just 500-600 degrees cooler than their environment. Sunspots emit less radiation and this is the reason why they look black on the surface of the sun. The sunspots by themselves are still many times brighter than the full moon. The reason why and when sunspots are formed on the sun is not clear yet but it is related to high electromagnetic energy activity. Sunspot regions are very active and can send strong CME (Coronal Mass Ejection) to space. If such CME is in the direction of earth, there might be noticeable events such as the polar auroras and interferences to the electricity network.

Every observation of the sun requires special  protecting equipment. Direct watching of the sun is very dangerous and can lead to blindness. Do not use old films, black glasses and their like. Only dedicated protecting filters are allowed. The writer takes no responsibility for any viewing of the sun.



History of sunspot observations
The first person to observe sunspots was Galileo Galilee. Although it is possible to see large sunspots with the naked eye during sunsets, we have no documentation of anyone in the ancient times noticing them. Galileo looked through his telescope (and without giving proper notice to the safety guidelines, thus becoming blind at the end of his life) and saw the spots. The previously perfect sun became imperfect which was another low to the old Greek opinion that all celestial orbs are perfect. Galileo noticed that each day the spots look a bit different and also that they are moving on the sun. In a long series of drawings from 1613 he proved and demonstrated that the sun revolves around its axis. Here is an example of Galileo's drawings, you can see many more drawing in the Galileo project site.  

Galileo's drawing of sunspots 1613
Galileo's drawing of sunspots 1613


Observing sunspots  with solar eclipse glasses
The most basic equipment are solar eclipse glasses. These glasses have a little solar filter film and it is safe to watch the sun with them. However most sunspots are too small and only big spots will be seen. Seeing the spots requires an optical device such as telescope, binoculars or long zoom camera.
Please notice that any solar filter must be in front of the first optical element. It is extremely dangerous to use solar eclipse glasses and then look through binoculars. The filters are not adequate for such use. The binoculars intensify the amount of the radiation and the filter will burn.

Creating a homemade solar filter
To view the sunspots through an optical device, a solar filter is required. A glass filter can be quite expensive, but there is a way to create a filter very easily. You need to buy a proper solar filter sheet (A4 size or whatever suits your need). You can make many filters from a single sheet for your camera, binoculars and so on. Looking through the filter you will see nothing except for very hot objects such as a tungsten light bulb.
Today there a DSLR-alike camera with 24x 30x or even 50x zoom lens which are very good for simple astro-photography. You can cut a square piece of kappa foam, make a circular hole in the diameter of your lens and stick a filter all over it. This will give you a proper solar filter. Make sure that the filter is firmly attached to the camera or binoculars and can't fall from it before use.
You will also need a tripod. Small cameras are not heavy and even a simple tripod will be good enough for most purposes.

Tungsten wire through solar filter
Tungsten wire through solar filter
I am using a Canon PowerShot SX50 HS for sunspots photography. It is a small and affordable DSLR like camera with 50x zoom (1200mm equivalent). The camera is not very expensive and this is how it looks with the solar filter attached.

The camera with the dedicated sun filter
The camera with the dedicated sun filter

Some more safety rules
When observing the sun with such filter observe the following rules.
  • Always make sure that the filter is attached firmly. 
  • Make sure that no one tries to touch or check the filter.
  • If you have to leave the area, do not keep the telescope aimed at the sun. Aim it the ground and cover the lens with the plastic cap. 
  • Check that the filter is not scratched or torn before each use.

How to photograph sunspots
Photographing the spots is simple:
  • Put the filter on the camera and aim to the sun. 
  • Use the maximum zoom that the camera has (20x and up) but do not use digital zoom.
  • Set the camera focus to manual at infinity
  • Set camera ISO to value between 100 and 400. 
  • Use the largest aperture possible to enable a shorter shutter speed. 
  • Use a tripod even at faster shutter speed. 
  • Set the light-meter to spot mode. Most of the frame is completely dark and average light metering will yield wrong results.
  • Experiment with the shutter release setting. Usually a little overexposure (+2/3) will improve the photo
  • Use a delay to eliminate "camera shakes" from pressing the camera button
The best hour for sunspots photography is around local noon. The sun is at its highest point in the sky and that can improve the quality of the photo. Due to the Earth rotating around its axis, the spots will change their place in the sun disc during the day. To see this just take photographs at the morning, noon and evening of the same day.
However the spots has a real movement on the sun disc, since the sun revolves around its axis once in 25-35 days. The sun is made of gas so its rotation speed is not the same in different latitudes. The slowest rotation is around the poles and the fastest around the equator. For this reason if you take a photo on the same hour for several consecutive days you will see the movement of the spots as the sun rotate. Try to compare your photos to professional photos such as in the Space-weather site.
Viewing and photographing sunspots is great fun for me. When there are large spots I usually take solar eclipse glasses and show other people what's happening on the sun. Many people, old and young are interested to see the sunspots.

Here are several photos from consecutive dates (almost). I tried to rotate the photos so they will be in the same alignment. The movement of the spots is clear. The sun is very dynamic. New spots are forming, old spots are decaying, and no day is the same. Even without dedicated solar scope, one can see the changing face of the sun.

Sunspots  14/02/2014
Sunspots 14/02/2014
The spots start to disappear behind the sun limb
Sunspots  16/02/2014
Sunspots  16/02/2014

Sunspots  17/02/2014
Sunspots  17/02/2014
 Most sunspots disappeared but other are coming out from the left
Sunspots  18/02/2014
Sunspots  18/02/2014

Sunspots  20/02/2014
Sunspots  20/02/2014


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