Spotting the zodiacal light in spring

The zodiacal light is a nocturnal phenomena that is revealed only to those who dare to escape the city lights. In spring, after sunset and once twilight fades away into a dark and moonless night, a gentle luminous band opens up when looking towards west. Its majestic cone then seems to stand high above the horizon, as if it was trying to guide the observer. In fact, the zodiacal light directs us to the very beginning of the solar system, roughly 4.5 billion years ago, when our Earth and the other planets were formed from and within a circumsolar dust disk. Although the solar wind steadily sweeps away dust, new dust grains are formed through outgassing comets and minor planet collisions. Most of these objects orbit the sun in a relatively well defined and narrow plane, which is called the ecliptic, i.e. the plane of the Earth’s orbit. As a result, the ecliptic is continuously fed with fresh dust and gas, which causes the redirection of sun rays through reflection and scattering, which are then captured as zodiacal light by some enthusiasts on Earth. Although zodiacal light can be seen all year round, spring and autumn are best suited for observations from mid latitudes, because then the path of the sun crosses the horizon at a steep angle, making the twilight zone short.

zodiacal light

Zodiacal light observed from Roque de los Muchachos Observatory, La Palma, Canary islands, Spain in April 2016.

Nikon D90 astromod VS. Nikon DF unmodified

It is fact that Nikon’s DF is among the most sensitive camera’s available on the market today. Its FX format CMOS chip offers 16.2 million pixels. The corresponding pixel size of 7.3μm is thus large compared to most other state-of-the-art cameras (with typical sizes of less than 5μm). As a result the Nikon DF has much better low-light, high-ISO performance.

However, as all unmodified cameras also DF’s CMOS detector is covered by an infrared (IR) blocking filter. This is unsatisfactory for astrophotography, in particular when imaging nearby star-forming regions. The reason is that young, massive stars emit hard UV radiation that leads to the ionization of the surrounding hydrogen. Subsequent recombination of free electrons with ions then produce strong emission lines such as the Hα line at approx. 656nm (in the red part of the spectrum). This wavelength unfortunately is already blocked by the IR filter found in almost all digital single-lens reflex (DSLR) cameras.

For that reason, some companies such as DSLR Astro Tec in Germany recently have specialized on modifying DSLRs. Different modifications exist, the one for astrophotography is basically a replacement of the IR-blocking filter with a clear-glass filter. This modification drastically increases the sensitivity of the camera at the wavelength of the Hα emission line. This modification comes at the cost of the camera’s white-balance, which then needs to be set manually. However, for astrophotography this doesn’t play a role anyway.

Since I own an unmodified Nikon DF and a modified Nikon D90, I was wondering how these two cameras would compare to each other when imaging star forming regions such as e.g. M8, the Lagoon nebula. In order to perform the test, I have used my Nikkor AF-S VR 200-400mm 1:4 lens, operated at 400mm f/4 and took images of the nebula using both cameras. In both setups the exposure time was set to 30 seconds at ISO 800. The result is shown below. Both images were taken in raw format and only brightness and contrast were adjusted in the same way. The result makes clear that an astro-modified D90 clearly outperforms even Nikon’s low-light market leader, the Nikon DF.

Nikon D90 astromod vs Nikon DF unmodified

Observing Comet C/2013 US10 (Catalina)

Comet C/2013 US10 (Catalina) was first discovered by the Catalina Sky Survey on October 31, 2013. It originates from the Oort cloud, a vast spherical reservoir of comets far beyond Neptun. By chance, gravitational perturbations can push Oort objects into the inner solar system, where they are eventually discovered. In some cases, comets get bright enough to be observed by naked eye or with small amateur telescopes or binoculars. The latter one is true for Comet C/2013 US10 (Catalina).

On Jan. 17, 2016 the comet passed its closest point to Earth at a distance of 110 million km. Using my 10-inch Newtonian telescope, I have imaged the comet that day from a suburban location. The result shown below is a stack of 17 frames of 120 sec. exposure time each. The inverted version on the bottom clearly shows the two tails of the comet.

Comet C/2013 US10 (Catalina)

Comet C/2013 US 10 (Catalina) imaged in L with a GSO 254mm f/5 Newtonian telescope and an ATIK 383L+ mono CCD camera

Comet C/2013 US10 (Catalina)

Comet C/2013 US 10 (Catalina) imaged in L with a GSO 254mm f/5 Newtonian telescope and an ATIK 383L+ mono CCD camera

 

Aurora Borealis – observed from Vallentuna

It is an amazing spectacle when a solar storm of charged particles hits the Earth’s magnetosphere. The particles following the magnetic field finally collide with particles of the Earth’s atmosphere – mostly oxygen and nitrogen. These collisions lead to either an ionization or excitation of atoms/molecules at an altitude of around 100 km. Subsequently, the recombination is responsible for the emission of a photon. The typically green colour arises from oxygen. On March 17, 2015 a strong solar storm hit the Earth and even at the relatively low latitude of Stockholm one could follow this energetic event.

Aurora Borealis observed from Vallentuna (Stockholm, Sweden)

Aurora Borealis observed from Vallentuna (Stockholm, Sweden)

Aurora Borealis observed from Vallentuna (Stockholm, Sweden)

Aurora Borealis observed from Vallentuna (Stockholm, Sweden)

 

Comet C/2014 Q2 (Lovejoy)

Comet C/2014 Q2 (Lovejoy) is bright (around 5mag) enough to be easily seen with binoculars or small telescopes in constellation Eridanus. On really good sites one should be able to spot it even with naked eye. However, currently the observing conditions are hard, because of today’s full moon. Additionally in the northern hemisphere the comet’s elevation is very low. I have spotted it two days ago from Vallentuna (near Stockholm, Sweden) when it was only 18 degrees above the horizon at maximum. I have taken some pictures with my CCD camera and was really impressed how fast the comet moves on the sky (see video).

The really good news is that the observing conditions are going to be better during the next days and weeks. C/2014 Q2 (Lovejoy) will climb further up, reaching constellation Taurus around 9th of January, just two days after it reaches the closest position to Earth at a distance of around 70 million kilometers.

Milkyway and Venus rise (Video)

The following timelapse movie shows the rising Venus and the Milkyway. The individual photographs from which the animated sequence was created, were taken at the Roque de Los Muchachos, La Palma, Canary Islands during an observing run at the Nordic Optical Telescope (NOT).

  • Roque de Los Muchachos, La Palma, Canary Islands, Spain
  • 3rd of March, 2014
  • Nikon D300 f/3.5 ISO 2500
  • exposure time per photograph: 20s
  • Time lapse interval: 120s
  • duration: approx. 1.5h

 

Planeten mit der Webcam

Jupiter

Jupiter

  • Datum: 21.04.2006
  • Zeit: 00h 00m
  • Ort: Sophienalpe
  • Aufnahmetechnik: Webcam: Philips ToUCam Pro (640×480 Pixel); fokal mit 2xBarlow am VC200L
  • verwendeter Filter: IR Sperrfilter
  • Brennweite: 3600mm
  • Blende: f/18
  • Belichtungszeit: je 1/250
  • verwendeter Film: CCD Chip
  • digitale Bildverarbeitung: Addition von ca. 500 Einzelbildern mit Registax, dann 2fache Vergrösserung

Saturn

Saturn

  • Datum: 20.04.2006
  • Zeit: ca. 23h 45m
  • Ort: Sophienalpe
  • Aufnahmetechnik: Webcam: Philips ToUCam Pro (640×480 Pixel); fokal mit 2xBarlow am VC200L
  • verwendeter Filter: IR Sperrfilter
  • Brennweite: 3600mm
  • Blende: f/18
  • Belichtungszeit: je 1/250
  • verwendeter Film: CCD Chip
  • digitale Bildverarbeitung: Addition von ca. 500 Einzelbildern mit Registax, dann 2fache Vergrösserung