Every netizen is aware of the hullabaloo around the solar eclipse that is about to occur on 17 August 2017. However, very few of us know why. This is going to be the first total solar eclipse since 26 February 1979. This one was visible from only five states of the US, and the weather was no help either. The upcoming one is causing the uproar because it will be a total eclipse that will be visible from at least 12 states of the US. This will be an event forever remembered in history and astronomy.
Why does solar eclipse happen?
We all know that the earth revolves around the sun while the moon revolves around the earth. When the moon comes in between the sun and the earth, it casts a shadow on the surface of the earth. The shadow is two distinct parts, the umbra (dark) and the penumbra (light). If you stand in the umbra, you will be able to see a total eclipse. This is actually quite rare, not because it happens rarely. It is rather rare because it mostly happens in the oddest places; deserts and oceans included.
Most of the times we see a partial eclipse because we are in the penumbra. Since the moon needs to be in between the earth and the sun, a solar eclipse happens only during the new moon.
What is so special about the 2017 solar eclipse?
The 2017 solar eclipse will be total, and it will cross the US from coast to coast. Anyone residing in the US on 21 August 2017 will be able to see the eclipse. In the far north, the eclipse will be partial. At least 14 states out of 50 will be able to see the total eclipse.
The path of totality is quite expansive. This is what makes the 2017 total eclipse so special in every way. The path length is about 70 miles. The path of totality will start from Oregon and end at South Carolina. Depending on where you are, the total eclipse can last for up to 2 minutes and 40 seconds.
During the time of total darkness, the other stars and planets will become visible during the daytime. This will be a spectacle to behold. This is quite a rare event, especially since NASA, the American Academy of Ophthalmology, American Astronomical Society (AAS), the American Academy of Optometry and the National Science Foundation have declared it safe to view the eclipse with naked eyes.
From which will the total solar eclipse 21st-Aug-2017 be visible?
This year, it is going to be truly unique. People across the states will see the sun disappear for a couple of seconds. The path of totality will stretch across Oregon, Idaho, Wyoming, Kansas, Illinois, Kentucky, Missouri, Nebraska, Georgia, Nebraska, North Carolina and South Carolina. NASA has an interactive map that shows the exact path the eclipse will take. There are several state-to-state guides as well, that will tell you the prime locations for better viewing of the diamond ring and total eclipse.
Not all solar eclipses are of the same length –
This happens because the distance between the earth and the sun and the distance between the moon and the earth are not statics. The distances vary from season to season. The distance between the sun and the Earth can vary by 3%. Although this seems minuscule in the dawn of a cosmic event, it is very critical for the duration of a total eclipse.
The distance between the moon and the earth are not constant either. This distance can vary by 12%. This results in a significant variation in the shadow cast by the moon. The diameter of the moon can relatively range from 7% larger to 10% smaller than the sun’s diameter during the event.
What causes the Baily’s beads effect during a total eclipse?
This is common during a total solar eclipse. Baily’s beads happen when the moon grazes the sun. The rugged topography of the lunar limb creates the appearance of “beads” during the eclipse. This occurs typically because the uneven surface of the moon allows sunlight to pass through some places and blocks the light completely in others. This phenomenongets it moniker after Francis Baily who explained the phenomenon in 1836. Depending on where you are viewing from, this phenomenon can last from a few seconds to a few minutes.
What is the diamond ring effect?
This is an exaggeration of the Baily’s bead effect. When only one ring is left, it is a diamond ring. This is a comparatively rare phenomenon. It looks like a shining diamond on the lunar ring caused by the silhouette of the moon. This usually occurs during the very beginning and the very end of a total solar eclipse.
Will the diamond ring form in the 2017 solar eclipse?
The diamond ring effect is usually fleeting. If you are standing in the penumbra, you will be lucky to see it for 2-3 seconds at the beginning or the end of the eclipse. Baily’s beads are more common than the ring effect. They are quite easy to identify. These are small specs of light that appear around the moon, dance around a bit and then face away to give way to one last bead creating the diamond ring effect.
This process is in reverse when a total eclipse ends. First, the diamond ring flashes into view. Then the other beads appear around the silhouette and finally the sun will come out of its cloak. Do remember to wear your protective eye-gear the whole time (except during the time of complete darkness).
What is the center line?
What would happen if the moon were square and so were its shadow? It definitely would not matter where you are standing as long as you are in the path of the eclipse. However, sadly, the mood is a sphere and its shadow is round. The longest duration of eclipse be along the center line.
You can easily calculate the duration of the eclipse on the center line with the following formula:
D = d/(1 – (1 – u)2)1/2 seconds
D: duration of totality on center line in seconds
d: duration of totality at location in seconds
u: umbral depth
What is the umbral depth?
The umbral depth is the relative position of a location from with regards to the center line and the path limits. You can calculate the umbral depth by the following formula:
u = 1 – abs(x/R)
u: umbral depth
x: perpendicular distance from shadow axis in kilometers
R: radius of the umbral shadow in kilometers
What causes less totality at the ends of the center line?
Two factors cause this variation in the duration of totality.
- As the shadow passes over the center line on the earth’s surface, the curvature causes viewers who are further away from the midpoint of the eclipse path to view a “smaller” moon. This is simply because they are further away, and the shadow of the moon appears smaller as compared to the sun. In other words, the cross section of the shadow is smaller, and as a result, it takes lesser time to graze across the surface of the sun.
- As you get closer to the end of the path, the shadow simply moves faster.
How to NOT view the eclipse?
Eclipses have been happening since prehistoric times. As long as the earth has been revolving around the sun and as long as the moon has existed, people have seen solar eclipses. Even then, very few of us know how to view the total solar eclipses safely. Here are a few things you must not do to protect your eyes from the harmful rays of the sun during the eclipse –
- Do not use eyepiece solar filters:
Plain eyepiece solar filters do not have the ability to filter UV rays. After unfiltered rays from the sun focus on a solar filter of this sort, it creates immense heat. This will cause the filter to crack, and the unfiltered sunlight will seep in.
- Do not use solar glasses to look through the telescope:
It is not just telescope. You should not wear solar glasses and look at the sun through binoculars or the camera either. The unfiltered sunlight can literally melt through the glasses and burn your eyes.
- Clouds are NOT a natural solar filter:
Though many of us want to believe that clouds are natural solar filters, for the lack of a proper filter to watch total eclipses, the truth is that clouds are no good in protecting your eyes from the high-intensity light of the sun.
- Exposed and old X-ray films are NOT enough to prevent UV rays:
When you are looking at the sun directly through developed x-ray films and camera films, they do little to stop UV and infrared radiations. They do not protect your eyes from visible radiation as well.
- Don’t use stacks of sunglasses to view an eclipse:
You should not use stacks of sunglasses either to see a solar eclipse. It may state that the procedure is 100% UV protective, but it rarely protects your eyes from all harmful radiations.
How to view an eclipse safely?
There are quite a few contraptions available that can help you watch an eclipse fully–
- You can get a shade 14 or darker welding glass. These glasses protect your eyes from intense, unfiltered light as well as UV and infrared radiation. A typical welding glass should make the sun appear green.
- Solar glasses are a very common method used to view the sun. They block 100% of the light. Solar glasses will protect you from both UV and infrared radiation. You can find a good pair of eclipse glasses online. This is ideal if you are not a part of the DIY trend. Even local natural history museums, astronomy clubs and space museums have an idea where to get proper solar eclipse glasses.
- Solar projection is a simple telescope back-end protection method. It focuses the image of the eclipsing sun on a flat, white surface. That can be a cloth or a thick paper. Always make sure that no one looks through the eyepiece. A huge disadvantage of this method is a threat to the telescope. Your telescope may damage if you are a novice. This is a process for experts only.
- A good alternative to a solar projection is a pinhole projection. This one is a natural way. It might sound quite bizarre, but dense foliage can act as small pinhole projectors. The small gaps between the thick leaves are okay for viewing the eclipse. Make sure you are not looking at the sun directly through the pinholes.
- Alternatively, you can use two cardboard pieces to make a more conventional pinhole camera. Take two pieces of white cardboard and use a sharp thumbtack to make a hole in the center of one. The hole needs to be round and smooth. Hold one paper above your shoulder and the other in front of you. The second paper acts as the screen. The sunrays filter through the first paper and focus on the second creating an inverted image. The added advantage of this project is – kids love it! The use of two simple cardboards to create a pinhole projector is ingenious and can become a part of any kid’s science project as well.
NASA and several other medical institutes are saying that it is safe to look through at the great American solar eclipse without any protection. However, it is only safe to look at the eclipsed sun with naked eyes when it is completely behind the moon. This state of totality may last for a few seconds only. If you are planning not to buy any protection for your eyes, you may miss out on some special events including the diamond ring and Baily’s beads. Therefore, if you want to make the most of this experience, be prepared with the proper gear!