How to capture scientific images of the Moon

Your images of the Moon can contribute to the analysis of unknown features, transient lunar phenomena and more, says The Sky at Night's Pete Lawrence.

Shadows are key to lunar study; as they move, grow and fade, new aspects of familiar surface features come to the fore. Credit: Pete Lawrence

Lunar images can play a part in scientific investigations of the Moon with the addition of a few key details. All lunar observations should be date and time-stamped and carry a record of the equipment used to perform the observation.

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Your name and location are also relevant, and seeing conditions should be noted.

For imagers, a five-point seeing scale such as that proposed by astrophotographer Damian Peach can be applied, where five equals excellent seeing and one extremely poor seeing. Also make a note of sky transparency.

Augment lunar observations with details such as phase, the Moon’s altitude and solar co-longitude.

The latter indicates the longitude of the morning terminator measured west from the central meridian; 0º at first quarter, 90º at full Moon, 180º at last quarter and 270º at new Moon.

This is especially relevant for features that only appear when the Sun is at a particular height in the lunar sky.

Get this information from freeware programs such as WinJupos or The Virtual Lunar Atlas.

Hardware & software you will need:

Hardware: Binoculars, small and large telescopes; DSLR and high frame rate cameras; infrared or red filter (for use with monochrome high frame rate cameras only).

Software: AutoStakkert!; WinJupos; Virtual Lunar Atlas; LunarScan (zip download); MetaGuide; Nudger.

Lunar photography projects:

1

Recording the extent of earthshine

High-contrast features may be visible under earthshine; these are some of the best to look for. Credit: Pete Lawrence
High-contrast features may be visible under earthshine; these are some of the best to look for. Credit: Pete Lawrence

When the Moon appears close to the Sun, it looks like a crescent. If you were standing on the Moon’s surface in the lit portion of the crescent, the Sun would be up and it would be day.

The dark portion would be experiencing lunar night.

Although the Sun would be below the horizon, the sky would be dominated by a bright gibbous Earth.

Sunlight reflected from Earth can illuminate the Moon’s dark portion, and we see this light reflected back to us as earthshine.

One of the simplest observations to make of the Moon is to record how bright the earthshine is.

This can be done with your eyes, through binoculars or a telescope.

A rough measurement with the naked eye would simply state whether earthshine was visible on a certain date and time or not.

Through binoculars or a telescope, it is possible to extend the estimate by stating which features, if any, are visible in the earthshine region.

Features such as the bright crater Aristarchus and the dark plain of Grimaldi make good markers for evening crescents, while
the bright crater Proclus and the dark Mare Crisium are useful for morning crescents.

Recording how late and early in the lunar cycle that earthshine can be seen is another useful measure.

A long-exposure image of the earthshine-lit Moon will reveal the dark portion almost as it would appear when fully lit.

For scientific purposes, comparison images at similar exposure settings should be taken.

Here, bracketing the exposures from a correct illumination of the sunlit surface to full overexposure of the same area is useful.

Earthshine records provide a valuable resource for monitoring Earth’s reflectivity, or albedo.

If Earth has a high proportion of clouds, its reflectivity is higher and the earthshine will appear more prominent, whilst a clear atmosphere on Earth will produce weaker earthshine.

For more information, visit the earthshine page in the Projects menu at the Big Bear Solar Observatory.

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Imaging lunar features

Different Sun angles create different shadow effects, as seen here at Crater Posidonius. Credit: Pete Lawrence
Different Sun angles create different shadow effects, as seen here at Crater Posidonius. Credit: Pete Lawrence

The Moon is covered in fascinating geological features – some easy to spot through small telescopes.

The surface has been extensively mapped and we now have online resources that allow you to zoom virtually into individual boulders (like this one available at QuickMap).

So with all of this data is there any point in observing and imaging the Moon at an amateur level? The answer is a wholehearted yes!

A number of factors change the appearance of lunar features over time, most importantly the monthly phase cycle and libration.

Taken together, these adjust the relative position of the Sun in the lunar sky, providing a multitude of illumination angles.

Amateur observers continue to build an extensive archive showing how lunar features change under this constantly varying illumination.

To add to the coverage, any images taken should be info-stamped with the values mentioned in the introduction.

Orientation should also be indicated and is especially important on high-resolution shots where navigational aids may otherwise be out of frame.

The Moon is unique in that, with north at the top, its eastern limb appears to the right.

While it’s customary to present lunar drawings with south up so as to replicate the view through the eyepiece, the ease by which digital photographs can be rotated has relaxed this requirement somewhat.

High-resolution imaging requires a telescope of at least 8 inches in aperture and a high frame rate camera to reduce the effects of atmospheric seeing.

Mono cameras are recommended and a long-wavelength pass filter – ie, red or infrared – can help steady the view.

Under excellent seeing, switching to a green filter may produce even sharper results.

Active programmes to record the appearance of specific types of lunar feature exist across organisations such as the Association of Lunar and Planetary Observers, the British Astronomical Association and the Society for Popular Astronomy.

These include banded craters, rilles, rays, high albedo swirls, domes, and dark haloes.

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Transient lunar phenomena

Video analysis can be carried out using the free LunarScan software as long as any positive results are relayed back to NASA.
Video analysis can be carried out using the free LunarScan software as long as any positive results are relayed back to NASA.

A transient lunar phenomenon (TLP) is a short-lived event observed or imaged on the lunar surface.

Much useful work in this area can be done by monitoring for surface impacts.

A lunar impact appears as a flash when the impactor vaporises. These may be seen on either the bright sunlit or dim night-time portion of the Moon.

Detection on the night side is easier because flashes have greater contrast against the darker surface.

The equipment required to capture TLP events doesn’t need to be particularly sophisticated, but there are a number of issues that need to be considered.

A full-disc image will give the best coverage, but any flashes detected are likely to appear tiny; increasing image scale will improve visibility at the expense of area covered.

An equatorially mounted telescope driven at lunar rate is necessary to keep the Moon in view; for long observing runs, autoguiding on the lunar surface is recommended.

Free programs such as MetaGuide or Nudger will do this for you. Monitoring is best achieved using low-light video cameras such as those made by Watec or Mintron.

Post-capture analysis can be performed using a free program called LunarScan.

This works with video frames up to 720×480 pixels, captured at 30 frames per second, equating to 12GB of storage per hour.

There’s a good quick start guide to using LunarScan online ; a condition of using this software is that positive results should be sent to NASA’s Meteoroid Environment Office.

Observing hubs such as the Association of Lunar and Planetary Observers provide good support for this exciting area of observation.

This includes predictions of favourable lunar meteor showers which, when active, increase the probability of recording an impact flash.

Submit your lunar pics for science

Prof Bill Leatherbarrow, director of the British Astronomical Association’s Lunar Section.

“In these days of robotic lunar exploration there are those who will argue that there are no longer opportunities for people with small and medium telescopes to contribute to the understanding of our nearest celestial neighbour,” says Prof Bill Leatherbarrow (pictured), director of the British Astronomical Association’s Lunar Section.

“While it is certainly true that backyard observers cannot compete with spacecraft imagery, there is still much useful science that they can do – more so now than when the Space Age began.

“High-resolution cameras allow detailed investigation of lunar geological structures, many of which have never been properly measured or had their distribution charted.

“Relatively time-rich amateurs don’t have to apply for allocated time on a large telescope, so they are in a better position than their professional colleagues to monitor transient events such as the flashes created by meteoroid impacts.

“The key to success is to work methodically as part of a team. The BAA Lunar Section will provide guidance on what kind of observational work is valuable, advice on how to present lunar observations, and opportunities for publication.”

Find out more at the BAA’s Lunar Section.

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This article originally appeared in the November 2017 issue of BBC Sky at Night Magazine. Pete Lawrence is an experience astrophotographer and a presenter on The Sky at Night.