The Solar Interior


The solar interior is separated into four regions by the different processes that occur there. Energy is generated in the core, the innermost 25%. This energy diffuses outward by radiation (mostly gamma-rays and x-rays) through the radiative zone and by convective fluid flows (boiling motion) through the convection zone, the outermost 30%. The thin interface layer (the “tachocline”) between the radiative zone and the convection zone is where the Sun’s magnetic field is thought to be generated.

The Core

The Sun’s core is the central region where nuclear reactions consume hydrogen to form helium. These reactions release the energy that ultimately leaves the surface as visible light. These reactions are highly sensitive to temperature and density. The individual hydrogen nuclei must collide with enough energy to give a reasonable probability of overcoming the repulsive electrical force between these two positively charged particles. The temperature at the very center of the Sun is about 15,000,000°C (27,000,000°F) and the density is about 150 g/cm³ (about 10 times the density of gold or lead). Both the temperature and the density decrease as one moves outward from the center of the Sun. The nuclear burning is almost completely shut off beyond the outer edge of the core (about 25% of the distance to the surface or 175,000 km from the center). At that point the temperature is only half its central value and the density drops to about 20 g/cm³.

In stars like the Sun the nuclear burning takes place through a three step process called the proton-proton or pp chain. In the first step two protons collide to produce deuterium, a positron, and a neutrino. In the second step a proton collides with the deuterium to produce a helium-3 nucleus and a gamma ray. In the third step two helium-3s collide to produce a normal helium-4 nucleus with the release of two protons.

In this process of fusing hydrogen to form helium, the nuclear reactions produce elementary particles called neutrinos. These elusive particles pass right through the overlying layers of the Sun and, with some effort, can be detected here on Earth. The number of neutrinos we detect is but a fraction of the number we expected. This problem of the missing neutrinoswas one of the great mysteries of solar astronomy but now appears to be solved by the discovery of neutrino masses.

The Radiative Zone

The radiative zone extends outward from the outer edge of the core to the interface layer or tachocline at the base of the convection zone (from 25% of the distance to the surface to 70% of that distance). The radiative zone is characterized by the method of energy transport – radiation. The energy generated in the core is carried by light (photons) that bounces from particle to particle through the radiative zone.

Although the photons travel at the speed of light, they bounce so many times through this dense material that an individual photon takes about a million years to finally reach the interface layer. The density drops from 20 g/cm³ (about the density of gold) down to only 0.2 g/cm³ (less than the density of water) from the bottom to the top of the radiative zone. The temperature falls from 7,000,000° C to about 2,000,000°C over the same distance.

The Interface Layer (Tachocline)

The interface layer lies between the radiative zone and the convective zone. The fluid motions found in the convection zone slowly disappear from the top of this layer to its bottom where the conditions match those of the calm radiative zone. This thin layer has become more interesting in recent years as more details have been discovered about it.

It is now believed that the Sun’s magnetic field is generated by a magnetic dynamo in this layer. The changes in fluid flow velocities across the layer (shear flows) can stretch  magnetic field lines of force and make them stronger. This change in flow velocity gives this layer its alternative name – the tachocline. There also appears to be sudden changes in chemical composition across this layer.

The Convection Zone

The convection zone is the outer-most layer of the solar interior. It extends from a depth of about 200,000 km right up to the visible surface. At the base of the convection zone the temperature is about 2,000,000°C. This is “cool” enough for the heavier ions (such as carbon, nitrogen, oxygen, calcium, and iron) to hold onto some of their electrons. This makes the material more opaque so that it is harder for radiation to get through. This traps heat that ultimately makes the fluid unstable and it starts to “boil” or convect.

Convection occurs when the temperature gradient (the rate at which the temperature falls with height or radius) gets larger than the adiabatic gradient (the rate at which the temperature would fall if a volume of material were moved higher without adding heat). Where this occurs a volume of material moved upward will be warmer than its surroundings and will continue to rise further. These convective motions carry heat quite rapidly to the surface. The fluid expands and cools as it rises. At the visible surface the temperature has dropped to 5,700 K and the density is only 0.0000002 gm/cm³ (about 1/10,000th the density of air at sea level). The convective motions themselves are visible at the surface as granules and supergranules.

Courtesy of

PLEDGE: Refuse Disposable Plastic

I pledge to refuse single-use and disposable plastic.

Take the Pledge

Plastic Pollution Coalition invites you to pledge to refuse disposable plastic as often as possible. Pledging is an important first step to changing. For those of you that already do refuse, stand up and be counted.

REFUSE pledge:

1. Say NO to all disposable plastics!

2. Reduce your plastic footprint. Consider the lifecycle of every plastic product you purchase. Choose products with the least packaging, look for products and packaging made from renewable resources, avoid plastic packaging and containers. Choose products that have the least amount of disposable parts. Choose glass and stainless steel over plastic.

3. Reuse glass and stainless steel containers and goods.

4. Recycle what you can’t refuse, reduce or reuse. Recycling plastic items is a last option, as in many cases your plastic recycling is shipped overseas, or ends up in the landfill.

5. Speak Out! Now that you are making a change in your life, send a message to government, business, and organizations asking them to join the Global Call to End Plastic Pollution, a pledge for institutions to help stop plastic pollution at its source.

Visit Plastic Pollution Coalition:

25 Useful Resources for Creating Tooltips With JavaScript or CSS



Tooltips are awesome, there’s simply no denying it. They provide a simple, predictable and straightforward way to provide your users with useful, context-sensitive information, and they look cool to boot.

We all agree on how great tooltips are, but how we go about implementing them can differ dramatically. If you’re at square one, looking for some tooltip ideas for your current project, you’ve come to the right place. We’ve got a whopping twenty-five different options that fall into two categories: JavaScript and CSS. No matter which method you’re looking to use, we’ve got the best techniques available.

JavaScript & jQuery

Tipped – The jQuery Tooltip

Let’s skip the idea of saving the best for last. If you don’t want to sift through twenty-five different options and figure out which is best, just download Tipped. The tooltips are attractive, easy to implement and there are a ton of options to choose from. You’ll have a hard time topping this one.


Opentip – The free tooltip

Opentip is another top-notch tooltip plugin. Like Tipped, there are tons of options so you can do pretty much whatever you want with them. The design of the tips themselves shows a little more character than those for Tipped, which might or might not be a good thing for you project.


Javascript Tooltip

Simple but effective. This one gives you positioning options, allows image embeds and can be triggered by a number of different events.


SkinnyTip JavaScript Tooltip Library

This one isn’t the most attractive option, but it is pretty lightweight. The entire library is less than 10kb so you don’t have to worry about it slowing down your page. It admittedly seems a little ancient, but it still works.


qTip – The jQuery tooltip plugin

qTip works in all major browsers, degrades nicely when JavaScript is disabled, is easily positioned, and features animations and rounded corners. It’s a really solid plugin and I highly recommend that you check it out. Also take a look at version 2.


Simpletip – A simple jQuery tooltip plugin

Simpletip is exactly as advertised. It not only looks simple, it’s super easy to use as well. There are also some visual loading effects that you can take advantage of if you want to take things further.


Tooltipster – The jQuery Tooltip Plugin

Ditch the plugins that have been around since Netscape. Tooltipster is a modern, HTML5 valid, awesome tooltip plugin. It’s lightweight, fast, browser-friendly and easily styled with CSS.


Tooltip – jQuery UI

jQuery users don’t have to go far to find great, robust tooltips, they’re built right into jQuery UI. They’re really simple and odds are you’ll find a ton of other stuff in the library that will make your site better as well.


TipTip jQuery Plugin

I love everything Drew Wilson does. He’s the guy behind Screeny, Space Box, Pictos and a bunch of other cool stuff. The fact that he made this plugin is enough to make me download it. At less than 3.5kb, this thing is super light and super amazing.



Tooltipsy puts the functionality in the hands of JavaScript, then uses clear, easily-customizable CSS for everything else. Change the appearance, size, animation; go nuts and make it your own.



Tipsy gives you very minimal and stylish tooltips without a bunch of fluff. It has all of the features that you need, like positioning and fade, and nothing superfluous that you’re never going to use.


Responsive and Mobile-Friendly Tooltip

This is a tooltip for the next generation of web design. It easily adapts to any size viewport and intelligently displays the tooltip in a size and position that is optimized for the current screen. If you’re doing responsive design, and you should be, you should look into responsive tooltips.


aToolTip – A Simple jQuery Tooltip by Ara Abcarians

aToolTip allows you to have a tooltip that constantly moves with your cursor or stays put over its partner item. It has hover or click options, is under 4kb and has callback functions.


Colortip – a jQuery Tooltip Plugin

Downloading a prebuilt tooltip plugin is cool, but why not take the plunge and learn to build one? Colortip is a free download, but it’s a part of an in-depth, step-by-step tutorial for building the plugin from scratch.


ChillTip jQuery Plug-In

ChillTip is a remarkable flexible tooltip plugin that allows you to implement the tips in a number of different ways. It can be used with span, img, anchor attributes and “pretty much anything else that uses the title attribute.”


Pop! Simple pop menus with jQuery

This is not quite a tooltip, but it’s closely related so I thought I’d include it anyway. Instead of having a little pop up on hover, this gives you a little clickable dropdown where you can hide extra information.


CSS Tooltips

CSS Tooltips

To start off the CSS tooltip section, we turn to master developer David Walsh. This tutorial focuses more on how to create the classic tooltip shape with CSS and less on how to successfully implement and pure CSS tooltip.


CSS Tooltip

This is a really awesome tool that allows you to easily build pure CSS tooltips simply by filling in a few fields. You can completely customize the appearance and contents using the simple form, then grab the code and paste it into your project.


Sexy Tooltips with Just CSS

A nice tutorial over on Six Revisions for creating really robust and attractive tooltips using CSS. The style is a sort of warning dialog look with an icon and colored box.


CSS Tooltip

A simple, lightweight, cross-browser, pure CSS tooltip. It’s a free download and only takes up a single measly kb.


CSS Bubble Tooltips

A simple, bubbly CSS tooltip. Not much here, but it works just fine!


Easy CSS Tooltip

This one is called “Easy CSS Tooltip” for a reason. It takes four lines of code: one line of HTML and three lines of CSS. That’s it! It doesn’t get much easier folks.


CSS Tooltips and Speech Bubbles

In this article, Konigi experiments with two different methods for delivering pure CSS tooltips. The first uses title and the second uses a span.


CSS Tooltips by Adam Whitcroft

Here Adam Whitcroft teaches you to build tooltips with data attributes. That might sound a little scary, but they’re actually really easy to use. Be sure to give this one a read.


Pure CSS Tooltips –

Here the author lays out a set of solid goals such as IE8 compatibility and minimal HTML, then shows you how he built some pure CSS tooltips that meet these goals. If you want a CSS tooltip that can be used in a professional, cross-browser environment, this is a good read.


What Do You Use for ToolTips?

Now that you’ve seen these twenty-five tooltip resources, it’s time to get out there and start making tooltips! Leave a comment below and tell us which resource you like the best or if you found any that weren’t listed above.

Joshua Johnson

Equal parts editor, writer, designer, & photographer. Hit me up on Twitter, read my Mac tutorials or check out my photos.

Zemanta plugin for has partnered with the folks at Zemanta to make blogging easier and faster by letting you quickly add recommended links, photos, tags, and related posts. With just a few clicks your post goes from simple to snazzy.

For a full set of questions and helpful answers on how to use Zemanta, please see this full detailed FAQ.

How to Activate Zemanta

To activate Zemanta, go to Users -> Personal Settings in your WordPress Dashboard.

You’ll see a new option near the end of the page called Additional Post Content that lets you add Zemanta to your posts. Selecting this option turns on Zemanta, and you can turn it off at any time by unchecking the box.

Be sure to save your changes by scrolling to the bottom of the page and clicking Save Changes.

There’s also a different way around on how to turn on your Zemanta plugin.

Click on Add new, just as if you would want to create a new post.

On the upper right corner you shall find the drop down menu called Screen Options. Tick the box next to Use Zemanta to find related content. For the Zemanta plugin to appear, you’ll have to refresh the site.

If you have already been doing some editing on your blog post, do not forget to save it, because WordPress doesn’t support auto-save function anymore! Here are some screenshots on where to find that option (click on it to expand).

After refreshing the site, Zemanta’s Recommendations widget should appear on the right side of your screen.

How It Works

When you create a new post you will see a Recommendations module in your edit post window. (You may have to scroll down fairly far in your edit window to find the module. You can drag the module up higher if you prefer — see screenshot above). Once you have started writing the post, you can click Refresh to have Zemanta generate recommendations for you.

The more information you have in the post, the more recommendations it can give you. Clicking Update will refresh the results, which is useful if the topic of your post has changed a little from the first time you hit the refresh button. The filter option is not your classic search as it still takes into account your text, but it also allows you to specify a term that the Zemanta recommendation engine should keep an eye out for while suggesting content

As you write your blog post, Zemanta is analyzing your text behind the scenes and picking up the most important keywords. These keywords are then translated into your suggested tags/labelsimagesrelated posts and in-text links.

In this example, the user has clicked on a recommended photo, as well as an article and a recommended link (located below the post). Zemanta automatically adds them into your post as you click on them.

Here’s how the post looks after it’s been spiffed up by Zemanta:

Pretty nice, eh? 🙂

A Few More Details

You can use as many of the Zemanta recommendations as you like, or you can ignore of all of them — totally up to you! Once you’ve added recommendations, you’ll need to manually delete any that you don’t want.

Currently, Zemanta works on English-language blogs. It only works in the visual editor mode. It’s not available on private blogs. Photos recommended by Zemanta are copyright-cleared, but we encourage you to check out the photo’s license if you have any doubts (you can do that by hovering over the photo).


Link Love – Why is linking out good for you (by Zemanta – social blogging) from zemanta on Vimeo.