The period in which Mars performs its journey round the Sun (called the sidereal period) is about 687 days; but owing to the Earth’s motion we are more concerned with what is called the planet’s synodical period of 780 days than with its sidereal period of 687 days. The synodical period is the interval between two successive conjunctions or oppositions of the planet as regards the Earth, and 780 days being twice 365 and 50 days over, it follows that we have an opportunity of seeing the planet at its best about every 2 years; and this is one of the reasons why Mars has been so much and so thoroughly studied as regards its physical appearance. Of course Mars is not equally well seen every 2 years, because it may so happen at a given opposition that it may be at its nearest to the Sun (perihelion), and the Earth at its farthest from the Sun (aphelion), in which case the actual distance between the two bodies will be the greatest possible. What is therefore wanted is for the planet to be nearest to the Sun and nearest to the Earth at the same time, under which circumstances it shines with a brilliancy rivalling Jupiter. This favourable combination occurs once in 7 synodical revolutions, or about every 15 years. The most favourable oppositions occur at the end of August, and the least favourable at the end of February. The next very favourable opposition will not occur until 1909. Mars may approach to within about 35 millions of miles from the Earth at a favourable opposition, whilst under extreme circumstances the other way it may be no nearer than 61 millions of miles at opposition. Mars in opposition is a very conspicuous object in the Heavens, shining with a fiery red light which has always been regarded as a peculiar attribute of the planet, so much so that its name, or epithet, in many languages conveys the idea of “fiery” or “blazing.” It is recorded that in August 1719 its brilliancy was such as to cause a panic amongst the public.