top of page

How Big Is the Sun?

Using Slooh’s Online Telescope and integrated Quest learning activities, you can capture your own images of the Sun and other celestial objects in each domain of space while learning more about their magnificent sizes. How Big? is one of 60+ curriculum-aligned STEM Quest learning activities on Slooh for students 4th grade to college.

Slooh’s Online Telescope:


How Big is the Sun?

Instead of reporting the physical sizes of objects in standard units of measurement such as kilometers, we prefer to think about their sizes in more relatable terms that are directly relevant to the domain. As such, let's think about the Sun in relation to the Earth's size, which we know very well. The Earth has an equatorial diameter of just under 13,000 kilometers. An equatorial diameter is the distance between two points on the equator that passes through the Earth's center.

So, while the Sun has a diameter of 1,392,700 kilometers, we can also think of it as being approximately 109 Earths wide!

Image by IXL

The Sun is classified as a G2 yellow dwarf star. Yellow dwarfs are medium-sized stars with masses between 0.84 and 1.15 times that of our Sun. So, although the Sun is the largest object in our Solar System, its size is just average when compared to other stars. There are billions of stars in the Milky Way alone, ranging from as small as Saturn to over 1000 times the size of the Sun. The table below will give you an idea of the vast span of sizes of some of the stars in the Milky Way in comparison to the Sun.


Solar Radii

Distance from Earth (light-years)

Proxima Centauri



Barnard's Star





8 light-minutes







Image by NASA


More About Slooh's How Big? Quest

You've seen many amazing photos of celestial objects, perhaps without knowing exactly what you are looking at, and over time you may have become a bit desensitized as to their majesty. On this quest, you will attempt to regain your perspective of these glorious celestial wonders.

Learning Objectives

By the end of this Quest, students will be able to answer the following questions:

  • What are the three domains of space?

  • What are the three standard units of measurement for each domain?

  • How do you convert the size of an object from unit to another?

Vocabulary Words

Standards Addressed


​RST.9-10.1, RST.9-10.2, RST.9-10.3, RST.9-10.4, RST.9-10.5, RST.9-10.10, WHST.9-10.2.E


HSN.Q.A.1, HSN.Q.A.2​

Related Slooh Quests

  1. How Far?

  2. Out With a Bang

  3. Stars Like Ours

About Slooh's Astronomy NGSS Aligned Learning Quests

Slooh’s Online Telescope is a learning platform designed to support any educator in teaching astronomy to meet NGSS requirements by collecting and analyzing real-world phenomena. No previous experience with telescopes is necessary to quickly learn how to use Slooh to explore space with your students.

You can join today to access Slooh's Online Telescope and all 60+ Quest learning activities if you are able to make astronomy a core subject of study for the semester or year. If you only have a few weeks to study astronomy, we also have a curriculum designed to fit your busy academic schedule and budgetary limitations. To learn more about our offers, click here.


bottom of page