Saturday March 3rd the outer planets Mars and Jupiter will be at a position along their respective orbits where they have the same heliocentric longitude of approximately 223o. However this does not mean that if you were to observe the two in the morning skies that they would be lined up. The are not. Rather, as this graphic shows, the two planets are lined up with each other and with the Sun, while the Earth is at a lower heliocentric longitude and not in the same line as the two planets.
Click here to go to the Qué tal in the Current Skies web site for monthly observing information, or here to return to bobs-spaces.
Saturday December 13th the planets Mars and Neptune are at heliocentric conjunction with both planets having approximately the same heliocentric longitude of 336.8o. From a perspective above the solar system the two planets are in a 
Yes there will be a transit of the Sun by Mars, however you would have to be on the planet Saturn to see this transit as this graphic shows. This astronomical event is known as a heliocentric conjunction. It is determined by measuring, along the ecliptic, the angle between the Earth’s vernal equinox longitude, 0o, and a planet as would be seen if you were on the Sun.