How to View Sun through Telescope : Astronomy for Kids
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How to View Sun through Telescope : Astronomy for Kids

Why not to see sun directly via telescope :

It’s quite hazardous to stare at the sun with your naked eye and to look at it with a telescope is far worse. Both can result in a big blind spot in the middle of human eye. Human eye has a lens in it which focuses the light on the back of your eye. Our telescope has a similar sequence of lenses that do the same.

How to View Sun through Telescope : Astronomy for Kids

The Sun is very bright celestial object and by focusing the light onto the back of your eye (the retina) with or without a telescope, you are putting a lot of energy (both optical light and infra-red) onto a tiny area. At some point in your life you may have tried to set paper on fire using a magnifying glass, so just think about that being done to the back of your eye. There is no sensation of pain at all as you have no pain receptors at the back of your eye.
So you will not even feel the damage being done, but later on you may find that you can’t see as you used to, and then – in some cases it eventually recovers but in other cases it is permanent.

There are also stories about Galileo Galilei turning blind eventually in his life due to constant exposure to harmful radiations.

Safety First!

Extreme care is necessary when viewing the Sun. The intensity of its light, when focused by even the smallest lens, is strong enough to ignite paper. The retina of an unprotected eye will be instantly destroyed, causing permanent blindness! Never look directly at the Sun without a proper solar-protection filter.

So, it is always advised never to look at the sun directly with the telescope.

Why can’t one use finder-scope to find the Sun:

We should never ever look through the finder scope when aiming our telescope at the Sun. In fact, you should always cover the front portion of finder-scope with an opaque material just to be safe. Crosshairs exposed to sunlight can melt in just a few seconds, and can result in burns or blindness due to unintentional exposure of our eyes to light passing through the finder-scope.

Instead, follow the shortest shadow technique, wherein we can keep an eye on the telescope’s shadow on the ground as you move the tube back and forth, up and down. When the tube’s shadow is shortest, the telescope should be pointed at the Sun.

Techniques to view Sun from Telescope :

The Sun in a telescope is an awesome sight, a dynamic, living body, changing unpredictably from day to day.  Depending on the method and the instrument used – it can reveal beautiful features such as sunspots, corona (during full solar eclipses), prominences etc.

However being extremely bright – 400,000 times brighter than the full Moon – the Sun poses a significant risk to our eyes if observed improperly. Normally we can’t look at the Sun for more than a few seconds since our eyes are forced to close to protect themselves.

It is easy to learn how to look at the sun as there are several right ways, there are also many wrong ways to view the Sun as well. The danger is obvious; the sun is so bright that prolonged, direct exposure can cause permanent damage to the retina, resulting in complete loss of vision or blindness. Hence, to observe the Sun safely, you need to filter out more than 99% of the sun’s light before it reaches our eyes.

The Sun is also the only celestial object hazardous to the observer. Without proper protection, even a glimpse of it through a telescope or binoculars can burn the eye’s retina and leave a permanent blind spot.

 Two Safe Methods of Solar Viewing

There are two ways to observe the Sun safely:

  1. bydirect viewing, with a proper filter over the front of the telescope
  2. byprojecting the Sun’s image onto a piece of paper.

Direct Viewing

In this technique we look at the Sun via telescope which is fitted with a solar filter. Proper solar filters are designed to fit over the front of a telescope or binoculars. By dimming the Sun’s rays before they enter the instrument, the dangerously high levels of solar radiation and heat are reduced, preventing permanent damage to both observer and optics.

These methods protect the eye against both visible and invisible radiations and the telescope itself against heat.

While using the direct viewing technique, be sure to attach the filter securely to the front of the telescope so wind or a careless finger can’t dislodge it while you’re gazing at the Sun!

 Solar Projection

When viewing the Sun via the projection method, follow these precautions for safe viewing:

  1. Cover the finder scope.
  2. Don’t aim the telescope at the Sun by sighting along the tube. Rather, move the tube until its shadow on the ground is smallest, while watching at a distance for light to come blazing out of the eyepiece.
  3. Use a low-power eyepiece.

One advantage of the projection method is that sunspot positions can be marked right on the paper.

Projection is wonderful for showing the Sun to a group of people all at once, but usually fails to reveal the fine level of surface detail visible with a filter. Filters provide a more detailed view, though they cost more and allow only one person at a time to view

Projection Method for Sun Spot Viewing

Projection Method for Sun Spot Viewing Source : http://astronomynow.com/2015/03/15/how-to-see-the-solar-eclipse-safely/

Solar Filters :

Solar filters work by blocking most of the sunlight to avoid any damage to the eyes. They are usually made from a durable glass which transmits 1/100,000th of the light. They are used for viewing the sun as a yellow-orange disk. With a telescope, these filters can view the details of the sun directly and safely, especially the sunspots.

There are two types of solar filters: white light and hydrogen-alpha.  White light solar filters are simply very dark neutral density filters.  These allow you to see sunspots on the surface of the sun and are ideal for viewing solar eclipses and transits of Mercury or Venus.  Hydrogen-alpha filters are narrowband filters.  These allow you to view solar flares, prominences, and other associated activity.

Solar filters fit over the front of the telescope, completely covering the aperture.  This is to protect not only the observer’s eyes but also the optics themselves.  The telescope’s optics would become very rapidly heated and potentially damaged without the filter in place.

 White Light Solar Filters

White light filters transmit the entire visible spectrum of light but attenuate it to a level that makes observing safe.  A filter designed for visual observation transmits only 0.001% of the sun’s light.  Solar filters look like mirrors because so little light is passing through them.

White light filters allow the photosphere of the sun to be observed.  It is the layer of the sun that generates most of the light and is therefore easiest to see.  This is also where sunspots occur, so these features are easily observed with white light filters.  Events such as partial and total solar eclipses and planetary transits are most often observed with white light filters.  However, solar prominences may not be observed with a white light filter and require the use of a hydrogen-alpha filter.

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Setting on sun via shortest shadow technique:

Sun being the brightest available object to an astronomer is not difficult to find with naked eyes. However, it is never advisable to search for sun via finder-scope or lens and we have already discussed about the hazards of viewing sun directly via scope. Instead, what we can do is follow another technique called shortest shadow technique, where a telescope is roughly pointed towards Sun and its shadow is observed. As the telescope is moved left-right, up and down, the length of the shadow of telescope tube will also change, and it will be smallest when the telescope is pointing exactly towards the Sun. This is known as shortest shadow technique of setting telescope on Sun.

Setting on sun via shortest shadow technique

Setting on sun via shortest shadow technique Soruce : http://chasingtotality.com/2015/08/

Sunspots

Sunspots are the spots visible on the photosphere layer of the Sun that appear visibly as dark black spots as compared to the surrounding regions. The sun generates very strong magnetic fields, and these sunspots are localized concentration of these magnetic fields into closed loops that results in their reduced surface temperature (approximately 4000 K) as compared to the surrounding photosphere (around 5780 K). Sunspots usually occur in pairs or groups of opposite magnetic polarity that move in unison across the face of the sun as it rotates.

Sun Spots

Sun Spots Source : http://science.nasa.gov/science-news/science-at-nasa

They can last anything from a few hours to a few weeks, or even months for the very biggest. Interestingly sunspot activity exhibits an 11 year cycle in terms of the position and number of spots.

Sunspots have two parts: the central umbra, which is the darkest part, where the magnetic field is approximately vertical (normal to the Sun’s surface) and the surrounding penumbra, which is lighter, where the magnetic field is more inclined. Only the smallest of sunspots, called pores, lack penumbras.

Sun Spots

Sun Spots Source : http://www.enchantedlearning.com/subjects/astronomy/sun/sunspots.shtml

The largest sunspots observed are reported to have diameters of about 50,000 km, which makes them large enough to be seen with the naked eye. Sunspots often come in groups with as many as 100 in a group, though sunspot groups with more than about 10 are relatively rare.

Watch Youtube Video on Sun Spot Viewing ith Telescope :

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