What is the evidence that early astronomers used to show that the Earth is turning on its axis?

What is the evidence that early astronomers used to show that the Earth is turning on its axis (or was it a growing understanding)? That’s a great question! Some of the early Greeks proposed that the Earth rotated on its axis to explain the apparent daily motions of the Sun and other stars in the … Read more What is the evidence that early astronomers used to show that the Earth is turning on its axis?

About 100 tons of cosmic dust fall on the Earth every day. Will this cause Earth’s orbit to change over time?

About 100 tons of cosmic dust falls on the Earth everyday, and this has been happening for billions of years, making the Earth heavier. Why doesn’t this cause our orbit around the Sun to change? The orbit of the planets is determined by the total mass in the system, and the dominant mass is that … Read more About 100 tons of cosmic dust fall on the Earth every day. Will this cause Earth’s orbit to change over time?

If the Moon was formed out of a giant collision, why is there no ring of debris surrounding Earth?

If the collision hypothesis about the formation of the Moon is correct, why is there no ring of debris around Earth? Surely the residual debris were not all swept up by the gravity of the Earth and the Moon. The collision hypothesis for the formation of the Moon (also known as the Giant Impact hypothesis) … Read more If the Moon was formed out of a giant collision, why is there no ring of debris surrounding Earth?

Is there public domain software to calculate the orbit of a spacecraft?

Is there public domain software that can calculate the trajectory of a spacecraft using a model of the solar system (that includes planets and moons)? Is it feasible for a group of high-school students to develop such a model for a fun (non-school, non-graded) project? The idea is to develop a model that would determine … Read more Is there public domain software to calculate the orbit of a spacecraft?

Why do comets not get captured by Earth’s gravity during a close flyby?

Seeing the Earth circles the sun and our Moon circles the Earth, why would a comet or asteroid, passing closer to Earth than the Moon, maintain its orbit and not get captured into Earth’s orbit? The reason, quite simply, is one of speed. The comet or asteroid is moving too fast to be captured into … Read more Why do comets not get captured by Earth’s gravity during a close flyby?

What proof do you have that planets are made from gas and dust?

What proof do you have that planets are made from gas and dust? The main way we study what planets are made of is by looking at their birthplaces around other stars. Planet formation happens in what are called “protoplanetary disks”. These protoplanetary disks are made of material leftover from the formation of the central star. … Read more What proof do you have that planets are made from gas and dust?