Astronomy Lab 3

Introduction: This lab involves the orbital motion between planets and other celestial bodies in the Solar System. Many things such as the force of gravity, mass differences and interaction between celestial bodies orbiting one another are key factors when it comes to motion. Kepler’s Three Laws of Planetary Motion will guide us through this lab and will hopefully answer many questions.

(Observations)

-Venus is the closest planet to Earth

-Mars is the furthest planet away from the Earth

-Mercury is between Venus and Mars

-Venus appears to be moving faster than Earth, while Mars appears to moving the slowest. Mercury also appears to be moving faster than Earth, however it has the least distance to travel.

1a) Retrograde motion is the motion of a planet or body that moves opposite to another body or planet. Due to planets orbiting at different speeds than one another, many seem to move backwards and in loops when being lapped by another planet. Earth and Mars for an example, both move eastward around the Sun. Earth is in the inner and smaller orbit, and moves faster than the orbit of Mars. When Earth passes the slower Mars, each planet sees the other as moving in loops or backwards relative to its usual motion in the sky.

Retrograde loops usually occur once every 6 months for Mercury, once every 7 months for Venus and once every 25.6 months for Mars.

A diagram of why and when retrograde loops occur is shown below.

Source: (http://cseligman.com/text/sky/retrograde.htm)

1b) Looking at the planets Mars and Earth right now, my partner and I were able to estimate that:

The last retrogression of Earth and Mars happened from January 20, 2010-March 3, 2012.

The next retrogression of Earth and Mars will be from April 7, 2014-May 19, 2016.

2) The asteroid AST is moving fastest when it is closer to the Sun and other planets, and seems to be moving when it is furthest away from the Sun and planets. Kepler’s Second Law of Planetary Motion states...