BBC Sky at Night Magazine

Although Mars has a very thin atmosphere, there’s enough to support weather and the formation of hazy clouds

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40 minutes longer than Earth’s, at 24 hours, 39 minutes and 35 seconds. This means that features are centrally located on Mars’s disc 40 minutes later on each consecutiv­e night. Imagine looking at Mars one night and seeing a dark feature at the centre of its disc (what’s known as Mars’s central meridian).

The following night at exactly the same time, that feature would appear slightly further east and take an extra 40 minutes to reach the central meridian once again. The night after that, viewing at the same time, the feature would take 80 minutes to reach the central meridian. It looks as if Mars resets position each consecutiv­e night, giving you just a glimpse of extra new surface along the western limb before it then does a re-run of what you saw on previous nights. Eventually of course, you do get to see the whole globe, but this ‘reset and re-run’ can catch observers out.

True colours

The light from Mars is predominan­tly shifted towards the redder end of the spectrum, which works in our favour because longer wavelength­s are less susceptibl­e to being blurred by our turbulent atmosphere. You can improve what you see visually with a telescope by using filters. Visual filters are normally identified by their Wratten numbers. These may be written as W followed by a number and possibly a letter. Although the numbers represent specific colours, there is no sequence to them; W16 is yellow-orange, W18B is very deep violet and W21 is orange for example. The letters sometimes found after the number represent increasing strength of filter.

Yellow filters (W12, W15) will tend to make the lighter, desert regions appear brighter and brown/blue regions darker. Orange (W21, W23A) also helps increase the contrast between the light deserts and dark exposed rocks, further cutting through the weak Martian atmospheri­c haze. Red (W25, W29) enhances the contrast yet again and is excellent for defining the boundaries between regions. Orange and red are also good filters to use for observing Martian dust storms, if they appear.

A green (W57) or blue-green (W64) filter is good for showing seasonal features such as frost patches, fog and irregulari­ties along the edge of the polar caps. Blue (W80A, W38, W38A), deep blue (W46, W47) and magenta (W30, W32) are all good colour filters for detecting Martian weather in the form of white clouds or limb hazes; magenta in particular is good for seeing detail in the Martian polar regions.

The last time Mars was at opposition in 2018, we got a view of it with a large apparent size, the best for some time and larger in fact than this year. But the planet was low to the horizon as seen from the UK and this spoilt the view for many. This year the Red Planet will get to a much higher altitude in the night sky, reaching at least 40˚ in altitude, in the constellat­ion of Pisces. With a maximum apparent size only fractional­ly smaller than that seen in 2018, this makes 2020 the year to get acquainted with this fascinatin­g world. ▼

What do you get when you combine a telescope with modern technology in order to create something new? A marvel for endless journeys through the Universe. Experience for yourself how even faint deep sky objects appear bright, clear and in full colour in the eyepiece. A cross between visual observing and fully automated photograph­y. Sounds too good to be true? It has been made possible through a combinatio­n of a telescope with an OLED screen and a state-of-the-art sensor. Welcome to the telescope world of the future. With the new Unistellar eVscope, the future has already arrived.

Fast aperture

The parabolic primary mirror produces an image with no spherical and chromatic aberration­s.

Integrated astro-camera

The highly sensitive Sony IMX224 CMOS sensor enables the observatio­n of even faint celestial objects.

Modern OLED screen

The night sky is projected through the eyepiece from an extremely high-contrast screen. You will see nebulae and galaxies in detail and in colour!

Autonomous Field Detection

This outshines convention­al GoTo! Thanks to the eVscope’s VRSKLVWLFD­WHG SODWH VROYLQJ SURFHVV LW FDQ DQDO\VH VWDUV LQ WKH HOG of view in seconds. So it automatica­lly points to every observing target.

Easy to use

With the Unistellar app (Android/iOS) you have complete control – uncomplica­ted and without irritating cables.

Enhanced Vision Technology

The eVscope shows not only the image from a single moment, but collects light over longer periods of time. So you can make even faint celestial objects visible! Activate the live stacking and watch WKH GHYHORSPHQ­W DQG RSWLPLVDWL­RQ RI WKH HOG RI YLHZ LQ UHDO WLPH

Convention­al telescope eVscope

 ??  ?? Pete Lawrence is an experience­d astronomer and a co-host of
The Sky at Night
Pete Lawrence is an experience­d astronomer and a co-host of The Sky at Night
 ??  ?? A good selection of coloured filters are useful additions when observing Mars
A good selection of coloured filters are useful additions when observing Mars
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