 The Sun is the final object we'll cover. It defines the entire solar system. But figuring out how far away it is is difficult. This is because we cannot see any nearby stars for parallax measurements. The Sun is just too bright. But total eclipses and passages of Venus across the face of the Sun as viewed from Earth have enabled excellent measurements. Here is a method that uses parallax to find the distance to Venus that in turn enables us to triangulate the distance to the Sun. Let's look at the motion of Venus in the sky relative to the Earth. As Venus orbits the Sun, it gets further away from the Sun in the sky, reaches a maximum separation from the Sun, corresponding to the greatest elongation, and then starts going towards the Sun again. By making observations of Venus in the sky, one can determine the point of greatest elongation. At this point, the distance between the Earth and Venus can be determined by a parallax at 104 million kilometers, or 64.6 million miles. The line joining Earth and Venus will be tangential to the orbit of Venus. Therefore, a line from Venus to the Sun at this point of greatest elongation is 90 degrees from the line between Earth and Venus. Drawing the line between the Earth and the Sun fills out the triangle. We call the length of this line that represents the distance between the Earth and the Sun an astronomical unit, or AU for short. The angle at the Earth is easily measured, 46.1 degrees. Now, using trigonometry, one can determine the distance, 150 million kilometers, or 93 million miles. Once the distance between the Earth and the Sun is known, one can calculate a number of other parameters. We know that the Sun subtends an angle of just about one half degree. As we did with the Moon, we can calculate the diameter of the Sun. At 1.4 million kilometers, or 860,000 miles. The surface area at 6.16 trillion square kilometers, and the volume at 1,440,000 trillion cubic kilometers, or 330,000 trillion cubic miles. The Earth's orbit is very close to circular, so with the Earth's orbital radius around the Sun being 150 million kilometers, the distance traveled in a year is the circumference of the circle. That's 942 million kilometers, or 584 million miles. Dividing by the number of hours in a year, we get the velocity of the Earth around the Sun, 107,500 kilometers per hour, that's 66,700 miles per hour. Now with the distance to the Sun, and our velocity around the Sun known, we can use Newton's equations to calculate the mass of the Sun at 2,000 trillion trillion tons. In fact, the Sun is 99.98% of the mass of the entire solar system. So as vast as our planet is, over a million Earths can fit into the Sun.