It’s pretty hard to get to grips with the scale of the solar system. It's really, really, really big.

To help process the vast distances within our system, astronomers use Astronomical Units where 1 AU is the distance of Earth from the Sun. If you see Venus in the night sky, our closest neighbour just 0.7 AU from the sun, it looks impossibly far away. But the further out you go, the more the distances multiply.

Earth and Venus are practically on top of each other compared to Uranus and Neptune. Neptune is a full 30 times the distance between Earth and the Sun.

Now think about the fact that our little solar system is over 250,000 AUs from our nearest star, which is, in turn, just one of many tucked away in a small corner of the Milky Way, which is only one of many galaxies that make up the known universe.

James O'Donoghue has made some brilliant videos about the solar system that explain this and more.

This sketch, and plenty more in the Starry-eyed Surprises section, features in my book Big Ideas Little Pictures

The original sketch of solar system sizes is on a paper background.

Paper background solar system sizes sketch

Dark sky background solar system sizes sketch

Solar system planets: how big is the solar system?

Everyone knows Everest is the highest mountain at a colossal 8,848m above sea level. But, depending on how you’re measuring, there are two other candidates for tallest mountain.

Mauna Kea is a volcano on the big island of Hawaii. In fact the whole island is made from volcano, so as a peak it rises from the base of the Pacific ocean to over 4,200m above sea level. Including the part of the mountain that rises from the sea bed it is over 10,000m tall.

Mt Chimborazo can also lay a claim to the tallest mountain. The Earth is not a perfect sphere — it bulges around the Equator meaning that points on the Equator are several kilometres further from the centre of the Earth than points further North or South. A bulging around the centre is a common shape for a spinning sphere due to the force exerted by the spinning. Sitting almost exactly on the Equator means that Chimborazo’s already enormous 6,263m from sea level makes its summit the furthest point on the Earth’s surface from the centre of the Earth.

I’m not totally sure if that means that at some point Chimborazo’s summit makes it the closest point to the sun, but it definitely sounds plausible! 

The 3 tallest mountains

The Earth’s tilt causes the changing seasons. As the Earth revolves around the sun, the tilt of its axis—23.5 degrees—causes the two hemispheres, North and South, to be either tilted towards the sun or away from it at different times of the year.

In Winter, because light from the sun hits at a greater angle and closer to the poles, the solar energy gets spread over a larger area. This makes it weaker and cooler and gives rise to colder weather (aka winter).

In summer, the sun's light hits more directly and is closer to the equator, so it’s concentrated on a smaller area, leading to hotter days.

Because of the tile of the earth, seasons are reversed in the two hemispheres, so if it’s winter in the Northern Hemisphere, it’s summer in the Southern and vice-versa. The further from the equator you go, the bigger the effect of the seasons. As an example, temperatures in Ecuador stay relatively constant throughout the year, while the poles experience extremes of 24-hour daylight or 24-hour night and great freezes and thaws.

A version of this sketch, along with a number of other planetary and seasonal ideas, features in my book Big Ideas Little Pictures

Planet sketches