Thursday, 16 February 2017

Auroras in Kiruna

On January 30th and 31st 2017, few ESAC Astro Club members observed and recorded an auroral burst over Kiruna, Sweden. It was possible thanks to the Mars Express  Science Working Team and Science Operation Working Group meetings celebrated at the Swedish Institute of Space Physics  in Kiruna on January 31st and February 1st, 2017.

Auroras observed near Kiruna on 2017-01-30. Credit: M.Castillo/M.Breitfellner, 2017

Auroras are produced when the Earth magnetosphere is perturbed by the capture of the charged particles (mainly protons and electrons) that constitute the solar wind. When the particles enter in the atmosphere they collide with the existing gases (mostly Nitrogen and Oxigen) and excite the atoms that later reemit the absorved collision energy. The dynamics of the light emission depends on the magnetic interaction between both the Earth magnetosphere and the particles. As the particles are captured mostly through the magnetic field poles, the auroral lights are seen at high latitudes of northern and southern hemispheres.

Auroras observed near Kiruna on 2017-01-31. Credit: M.Castillo/M.Breitfellner, 2017

The solar wind stream depends on the solar activity cycle of 11 years. So, when the solar activity is high it is more probable to see auroras because there are more intense particle ejections. Currently the Sun is moving to the minimum of the present solar cycle, so the solar mass ejections are not very intense. However, other solar features release significant streams of charged particles. The Sun´s corona acts as a shield that decelerates and reduces the solar wind normally ejected from the photosphere. As the corona is constantly changing and reshaping due to its interaction with the solar magnetic field, sometimes an area opens in the corona, then a coronal hole is formed. As a consequence the solar wind increases significantly and it is followed by intense auroras around the Earth poles.

The observed auroral burst was produced by a G1 (Kp5) geomagnetic storm due to the arrival of a high speed solar wind from a large coronal hole in the Sun. This coronal hole can be observed in this video link of the Solar Dynamic Observatory of NASA. It formed behind the Sun and when it rotated and pointed to the Earth it released the charged particles that three days later produced the observed Auroras. A video showing the observed auroras in real time is here.

Friday, 10 February 2017

Sun Dogs - Parhelia

A really bright Sun Dog (parhelia) was visible on 09 Feb 2017 from Majadahonda. Gently falling hexagonal ice plates create this sky spectacle. The ice particles are located in the distant cirrus cloud formation. The vertical extent of the red hue seems to indicate large crystals, as they are subject to larger wobbling while falling.

Left Sundog with increased brightness towards the parhelic circle

Parhelia on cirrus cloud

If you want to learn more ..

Sundog formation (courtesy ATOPTICS)

ISS and the Moon over ESAC

On Saturday 14th 2017 the International Space Station ISS crossed the disk of the Moon as seen from the European Space Astronomy Center, ESAC. 

ISS crosses the Moon video

The image is a superposition of thirteen consecutive frames captured on 14th January at 02:01:14. The phenomena is extremely fast: the ISS took only 0.56 seconds to cross the moon disk! Therefore careful location/timing planning was required to successfully capture it. The ISS was in Earth's shadow, so its black silhouette is clearly seen against the bright background of the Moon surface.

ISS crosses the Moon

ISS-Moon crossings are common, but a crossing from a specific location on Earth is not. The observer, the ISS and the Moon must be precisely aligned. The ISS is the largest man-made object in orbit, spanning the size of a football pitch. Despite its large size, it orbits the Earth at a distance of approximately 400 km, therefore looking tiny to telescope fanatics. Depending on the ISS orbit altitude and the Moon elevation over the horizon, our natural satellite is at least 30-40 times bigger than the man-made station. The geometry is so particular that the ground path where observers can see the event is only a few hundred meters wide. Therefore careful planning of the observation must be performed. The station flies at ~27000km/h therefore the transit takes is a blink of an eye to be complete.
An ESAC group composed of Michel Breitfelner, Manuel Castillo, Abel de Burgos and Miguel Perez Ayucar set up two telescopes with two Canon reflex cameras in the back of the A-building, in the freezing night. The ISS, being in Earth's shadow, cannot be spotted before the crossing, so the observation is done with a clock in hand, and basically in the blind. Everything was right at the precisely expected time. The outcome was awesome: seen a fast dark spot carrying astronauts, flying cross the Moon.