Wouldn’t it be nice to be able to see the planet Mars from your backyard as it appears in this Hubble image? Sure, it would, but even though Mars is the only planet that reveals surface details in amateur telescopes, it is a small planet located a very long way away, which can sometimes make it a challenging affair to discern any surface detail at all. Nonetheless, despite the occasional difficulties in resolving surface details, it is possible to obtain stunning views of the red planet, and here is how to do it.
Mars is not particularly difficult to find because like the other planets, it lies close to the ecliptic, which among other things, represents the plane of the solar system. However, since the ecliptic is inclined with respect to the celestial equator (which corresponds to the earth’s equator), by 23.5 degrees, the location of an observer on Earth plays a major part on how high above the horizon Mars, or any other planet, will culminate, or be seen to rise. In practice, the further north of the equator an observer is, the lower above the horizon Mars will be at its highest elevation at the midpoint between rising and setting.
Moreover, since Mars orbits the Sun once every 687 days, there inevitably comes a time that it approaches the Sun as seen from our perspective. As Mars approaches the Sun, it sets progressively earlier after sunset, until it re-emerges from behind the Sun (from our perspective), to rise again as an early morning, pre-dawn object. This is of course a gross oversimplification of Mars’ orbital motion, but it serves to illustrate the point that the planet is sometimes not visible.
There are many online resources that list the position of Mars on any given date, and it is recommended that novice observers familiarize themselves with the planets’ periods of visibility. Nevertheless, even when Mars is visible, there are times when it is closer to Earth than at other times, and it is during the latter moments, called “opposition” when the best views of the planet can be had.
The image above illustrates this very clearly. Opposition occurs when Mars is at its point of closet approach to Earth, but because neither Earth’s, nor Mars’ obits are perfectly circular, or concentric with respect to each other, the actual distance between the two bodies at any given opposition can vary considerably: the image above shows the actual distance between Earth and Mars at opposition on the dates shown.
One more complicating factor that influences how well Mars can be seen is the fact that the planets’ disc is fully illuminated only at opposition. At other times (before and after opposition), a part of the disc is in shadow, meaning that the phase, or illuminated portion of the disc changes all the time, albeit at longer intervals than happens on the Moon.
Seeing Mars at it’s best
While any telescope can deliver views of Mars, the general rule is that the bigger the instrument, the better the view, since bigger instruments gather more light. However, atmospheric conditions can play havoc with even the biggest instruments, meaning that seeing conditions must be good, and the planet must be as high above the murk of the atmosphere close to the horizon as possible to get the best views.
Assuming then that seeing conditions are excellent, and that Mars is at its highest elevation above the horizon, (which happens late at night), a refracting telescope of minimum 4 inches, or a reflecting instrument of at least 6 inches aperture will resolve the planets’ phase, as well as features like the very bright polar ice caps, and colour variations on the surface.
However, telescopic views of Mars can be greatly enhanced by using suitable filters to block out light frequencies that either absorb, or scatter light from Mars gathered by the telescope. For instance, an orange filter such as a Wratten #25 filter will enhance the subtle difference in surface colours if you are using a relatively small instrument, while a red filter in the eyepiece will do the same on large instruments. Similarly, using a pale blue filter on both big and small instruments will accentuate the polar ice caps and some types of white clouds.
Moreover, regardless of the telescope aperture you need large magnifications for the best results- typically upwards of 175×. However, it must be remembered that no matter how good the seeing conditions are, or how expensive the equipment you use, no view of Mars through amateur equipment can ever come close to photographic views, since cameras capture light in ways that human vision cannot. The image below shows a view of Mars through a 6-inch refracting telescope, but bear in mind that this image had been somewhat enhanced by the photographic process.
Much of the surface colour contrast shown here is not visible to human vision through a telescope, but some experimentation with filters and magnification might produce views that come close to this excellent amateur picture, especially in large instruments.
What to see on Mars
While a 4-inch refractor or 6-inch reflecting instrument will show subtle albedo (colour) variations on the Martian surface, 6-, and 8-inch reflectors will reveal cloud structures in the planet’s atmosphere, of which there are several types. Below are some details-
This type of cloud tends to persist in one particular area as the planet rotates. Most cloud structures of this type occur in the Martian northern hemisphere during spring and summer there, and these clouds are best viewed through pale blue filters.
Clouds of this type consist of water ice, and they are formed at different levels in the Martian atmosphere as winds pass over high mountain peaks and the tops of high volcanoes. Orographic clouds at high altitudes are best seen through pale blue of violet filters, while low-level orographic clouds are best seen through various shades of green filters.
Morning and evening clouds
Morning clouds form much like, and for the same reasons, that fog forms on Earth. Note however that morning clouds usually only lasts for a few hours after Martian sunrise, while evening cloud structures are usually larger, and form as Martian night approaches.
One more thing
When viewing Mars, some light pollution might actually work in your favour. For instance, a white light off to the side will have the effect of activating your daytime vision, which is significantly superior to your night vision in both colour sensitivity and resolution.