April this year is a special time for astronomers as Mars the intriguing "Red planet" reaches opposition on the eighth of the month. On this day, Mars rises in the east as the Sun sets in the west, remains visible all night long before setting in the west as the Sun rises once again in the east. During April, the planet is also at its brightest and has its largest apparent size for the year. With a magnitude of -1.5, Mars is unmistakable amongst the stars of Virgo. The planet dazzles with a deep red-orange hue; shining at about the same brightness as Sirius, the brightest star in the night sky.
What makes a Mars opposition special is that they don't occur as often as the other outer planets. Generally speaking, Jupiter, Saturn, Uranus and Neptune reach opposition once per year. However, Mars takes roughly 2 years and 2 months or 780 days from one opposition to the next! The reason for this is due to orbital dynamics; Mars moves fast compared to the other outer planets and hence the Earth takes twice as long to catch up with it.
What to expect this year
The orbit of Mars is eccentric which means the difference in distance between its closest point to the Sun (perihelion) and its furthest (aphelion) is considerable. At perihelion Mars is 1.3815 AU (206.7 million kilometres or 128.4 million miles) from the Sun whereas at aphelion the distance increases to 1.666 AU (249.2 million kilometres or 154.9 million miles). This corresponds to an orbital eccentricity of 9.3%, compared to just 1.7% for the Earth. As a result, the brightness and apparent size of Mars at opposition greatly depend on the location of Mars in its orbit at that time.
Although better than the opposition of 2012, Mars in 2014 is closer to its aphelion orbital point than to its perihelion point. It presents an apparent disc of 15.2 arc seconds in diameter this year, which is slightly larger than the 13.9 arc seconds of 2012 but much less than the 25.1 arc seconds achieved at the historically close 2003 opposition. The next really great opposition of Mars will occur in 2018.
Mars always appears in the southern section of the sky during the best oppositions, favouring observers at southern latitudes. However, on this occasion the planet has a declination of -5 degrees and therefore is reasonably well placed for observers located at northern temperate latitudes as well. On April 14, closest approach to Earth occurs when 0.6176 AU (92.4 million kilometres or 57.4 million miles) separates the two planets.
It's now summer in the northern hemisphere of Mars, which means the North Pole cap of the planet is tilted towards the Earth. When viewed through a small 100mm (4-inch) telescope Mars appears small but under good seeing conditions it's possible to spot the polar cap as well as other major surface features such as Syrtis Major and various dusty shadings. On initial observation the planet may appear bland but with time and patience it's possible to tease out details. In addition, don't be afraid to push up the magnification as high as possible as Mars is a planet that will take high magnifications. Larger telescopes allow more subtle details on the planets surface to be seen. The co-ordinates of Mars at opposition are: R.A. = 13hr 12m 56s and Declination = -5d 03m 24s (J2000).
For the next two or three months Mars is at its best so take the opportunity to observe this wonderful planet.