What is a lunar eclipse good for?

- The moon darkens considerably during eclipses, which offers a unique opportunity for observing impacts against its surface.

- Researchers from The Instituto de Astrofísica de Andalucía (IAA-CSIC) have programmed moon observations from different places in order to detect and study impacts on the moon during next September 28th eclipse.

- The most sophisticated observations will be carried out from the Calar Alto Observatory 3.5m Telescope.

Next Monday, September 28th, from 03:07 the earth will intercept the sun light going to the moon, and it will produce a total lunar eclipse, a phenomenon that darkens considerably our satellite and, besides it constitutes a beautiful astronomical spectacle, it will also allow scientific studies. IAA and Huelva University researchers will observe this event from five different observatories for detecting fragments from comets or asteroids impacting against the moon surface.

“This eclipse will bring us a very special opportunity for this kind of studies, as with the darken of the moon we can detect much weaker sparks as when we observe the moon night side, and we also can see a much bigger moon area than with ongoing projects, like MIDAS”, José Luis Ortiz, IAA-CSIC researcher points. He has coordinated next Monday observations.

“Besides, this year, and during present dates, we’ll be able to observe collisions due to what is called Taurid Complex, which this year could be specially intense, so we could study collisions of fragment from Enke Comet or from a bigger progenitor comet”, Ortiz said. His research group will observe this event from different places, most notably the Calar Alto Observatory 3.5m telescope, and using distinct techniques, observing in both the visible and the near infrared.

Impacts on the moon

These impacts are mainly produced by fragments that come from comets and asteroids that orbit the sun, and technically known as meteoroids. The Earth has a protective atmosphere that avoids that most of the meteoroids impacting against it could reach the ground, but the moon hasn’t this shield and even the smallest fragments can hit his surface and can produce a crater.

As this kind of impacts occurs at speeds of tens of thousands kilometers per hour, the rocks melt and vaporize instantly at the point of the impact. “Due to this, we do not call meteorites this collisions, as this term implies fragments”, José Luis Ortiz (IAA-CSIC) explains. The impact produces a sudden temperature rise resulting in a fraction of second flicker observed with Earth telescopes.

The results obtained from the analysis of these impact flashes on the Moon allow knowing the frequency with which meteoroids collide with the Earth. On September 11th, 2013, MIDAS project group detected the most brilliant impact against the moon ever observed, produced by a rock with the mass of a little car. The conclusions of this investigation indicated that the frequency with which impacts of similar sized rocks occur against our planet, could be nearly ten times greater than scientific community thought.

Lunar eclipse characteristics

During a lunar eclipse, the moon is not hidden at all, but it is darkened considerably and turned into red. This coloration is because, although the moon is hidden by Earth, it receives some of Earth atmosphere refracted sun light. The light that reaches the moon surface has come a long way through the atmosphere and is very red, as it happens on sunsets. And, like during the twilight, the coloration will depend on the atmospheric conditions, so it will never be two identical lunar eclipses. The amount and color of the light reaching the Moon during the totality phase is especially sensible to the amount of particles within Earth stratosphere.

“We can determine the amount of particles observing the eclipse, and this has interest due to its big influence over the atmosphere energy balance, which at the same time, has an important relation with global warming”, Ortiz (IAA-CSIC) points.

Lunar eclipses are much more frequent than solar ones and, unlike these, it is not needed using any kind of eye protection for observing them. Next September 28th eclipse (early Sunday to Monday), will occur in different phases and on next times:

The German-Spanish Calar Alto Observatory is located at Sierra de los Filabres, north of Almería (Andalucía, Spain). It is jointly operated by the Instituto Max Planck de Astronomía in Heidelberg, Germany, and the Instituto de Astrofísica de Andalucía (CSIC) in Granada, Spain. Calar Alto has three telescopes with apertures of 1.23m, 2.2m and 3.5m. A 1.5m aperture telescope, also located at the mountain, is operated under control of the Observatorio de Madrid. 

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