In space, there is no air. Because there is nothing for the light to bounce off, it just goes straight. None of the light gets scattered, and the "sky" looks dark and black.

In the night sky (and to some extent during the day) the moon, planets and stars are visible in the sky.

During a sunrise, the sun is lower in the sky, which lengthens the angle at which light reaches the Earth. As a result, the shorter violet, blue and green light never reaches the eye, so only the yellow, orange and red light is visible. Because red has the longest wavelength, the first light of dawn often appears pink or red--depending on the particles in the atmosphere. As the sun moves further up the sky, the reds and yellows fade as the scattered blue light becomes more visible.

Sunlight reaches Earth's atmosphere and is scattered in all directions by all the gases and particles in the air. Blue light is scattered in all directions by the tiny molecules of air in Earth's atmosphere. Blue is scattered more than other colors because it travels as shorter, smaller waves. This is why we see a blue sky most of the time

As the Earth rotates it turns away from the sun’s light, and the sky becomes dark. However, if you think about the millions and millions of bright stars all around the sky at night, you might start to wonder why it isn’t just as bright as it was when we were facing the sun!

As the light from our Sun shines into the atmosphere, most of the colors are able to reach the Earth’s surface uninterrupted. However, because blue light has a wavelength that is the same size as the particulates in the air, this light is scattered in every direction. This blue light bounces from particulate to particulate until it eventually reaches your eyes. For this reason, no matter what direction you look in the sky, it appears to be blue. This blue light originated with the Sun, was bounced around in the sky many times, and then eventually reached your eyes.

The wavelength of the blue light scatters better than the rest, predominates over the other colors in the light spectrum, and makes the sky appear blue to us.

Use the “Save” option to bookmark a page. Bookmarking saves a link to the page in your online Diigo library, allowing you to easily access it later.

Highlighting can also be accomplished from the context pop-up. After the Chrome extension is installed, whenever you select text on a webpage, the context pop-up will appear, allowing you to accomplish text-related annotation. Highlight Pop-up Menu – After you highlight some text, position your mouse cursor over it and the highlight pop-up menu will appear. The highlight pop-up menu allows you to add notes to, share, or delete the highlight.

Sticky Note Click the middle icon on the annotation toolbar to add a sticky note to the page. With a sticky note, you can write your thoughts anywhere on a web page.