What the Sun's crown is

Beyond the chromosphere is the Sun's ultra-thin halo of boiled-off gases which is known as the corona. This is the crown of the Sun. Its glowing white hot atmosphere is seen only as a halo when the rest of the Sun's disc is blotted out by the Moon in a solar eclipse.

Why blood is red

Each tiny drop of blood contains up to five million red blood cells that give blood its colour. Red blood cells contain a substance called haemoglobin which takes in oxygen in the lungs. Blood that is rich in oxygen is bright red.

As this bright red blood is pumped around the body, the oxygen is gradually taken up by the body's cells. By the time the blood returns to the heart, it is slightly darker, more rusty red than the bright red blood which left the heart.

What inner planets are

The four planets in the solar system that are nearest to the Sun are known as the inner planets. They are Mercury, Venus, Earth and Mars.

All the planets are small planets made of rock, unlike the bigger planets further out which are made mostly of gas.

Because the inner planets are made of rock they have a hard surface on which even a spaceship could land on. And so they are sometimes called terrestrial (Earth) planets. They all have a thin atmosphere, but each one is very different to the other.

How wind-blown sand shapes scenery

Sand plays a key role in shaping scenery, especially in deserts. Winds lift grains of sand which are then blown and bounced forward. Sand grains are heavy and seldom rise over two metres above ground level.

However, at low levels, wind blown sand acts like sand-blasters. The wind blown sand polishes rocks, hollows out caves in cliffs and undercuts boulders. Generally, boulders whose bases have been worn by wind-blown sand are top-heavy and mushroom-shaped, perched on narrow stems.