This is where you’ll find our thoughts about recent (and not) astronomy, earth science and other science news, our answers to questions we get from people a lot, plus whatever else strikes our fancy. Sometimes we get into a few of the mathematical or scientific details, but never too deeply.

Earth's orbital motion around the Sun means that we view different parts of the sky in different months of the year. (Image generated by SkySafari.)

#### What Stars Are Visible at Different Times of the Year?

As Earth orbits the Sun, the apparent position of the Sun against the background stars changes. As a result, we see different parts of the sky at different times of the year. This annual motion of Earth around the Sun is what gives us our “winter sky” and our “summer sky,” respectively.

In response to a question from the public…

#### Why Are Galaxies Disks?

Not all galaxies are disks, but many are. The reasons have to do with their formation history and a few basic physical laws.

Stars are basically giant balls of hydrogen and helium gas, and little else. However, the "little else" matters.

#### What Are Star Types?

You might have heard that there are different kinds of stars, called stellar types or stellar classes. You might have also heard that these types have cryptic names designated by letters of the alphabet. This post explains what these stellar types are and how they came to be.

Ever falling, ever missing…

That is an orbit.

#### What Is An Orbit?

In simplest terms, an orbit is the path of a planet around the Sun, or of a satellite around its parent body. The Moon orbiting Earth is an example. But what causes the orbit to have one size and not another? It turns out that all of the properties of an orbit are the result of two physical laws: the law of energy conservation and the law of conservation of angular momentum.

Many quantities in the world have both a size and direction associated with them. These are called vectors.

#### What Are Vectors and How Do They Work?

Vectors are mathematical objects. They are too complicated to be described by mere numbers, but like numbers, vectors have a size. However, they also have a direction. As such, they can be used to mathematically describe certain physical items that also have a size and a direction.

Velocity is an example of such a vector quantity; it has both a size or amount (speed) and a direction. What do we mean when we say that a velocity has a direction? A velocity is always forward, back, left, right, up, down or some combination of these. This makes it a perfect candidate for a vector description.

In this article we outline the basic properties of vectors, provide several examples of physical quantities that are described by them and also demonstrate how they are used to describe the world.