Thursday 30 August 2018

NGC6804 and its curious dust disk

NGC6804 is a fairly advanced planetary nebula in the constellation of Aquila, the eagle. In spite of its distance of 4,200 light-years, a high surface brightness makes this nebula an easy target for small to medium telescopes. Its outer shell has reached a diameter of 1.3 light-years and therefore its expansion is slowing down due to the interaction with interstellar space. 

Yet there's more to this fine planetary than its three shells reveal at first sight. Invisible to human eyes, this planetary emits a significant amount of radiation in infrared wavelengths, much like NGC7008. The cause for this is a large dust disk surrounding the white dwarf, probably rubble and debris of a planetary system that once existed but that has died along with its progenitor star. Within the next 5 billion years, also the Earth will follow the same tragic fate.

Friday 10 August 2018

IC4954/5: Shedding the birth veil

Some six degrees north of the famous Dumbbell Nebula, at the border between the constellations of Vulpecula and Cygnus, dwells a small star cluster. Roslund 4 is not all that difficult to observe, in spite of its considerable distance of 6,000 light-years, and should already be visible through a three-inch telescope given good sky conditions. 

A bigger challenge is the surrounding nebulosity (IC4954 - IC4955) which reflects the light of the stars in this cluster, born out of it hardly 4 million years ago. The young, hot stars have fired up nuclear fusion at full power and the ensuing radiation, up to 3,000 times solar, is currently blasting the nebula away. The sharp edge where the stellar wind's hitting the nebula actually serves as a very convenient yard stick with which we can measure the expansion speed of the nebula. It is estimated that within the next 6 million years the nebula, still containing about 60 solar masses of matter, will have dissolved completely. 

Thursday 9 August 2018


The red planet has fascinated mankind since the dawn of civilisation due to its remarkable colour, even when viewed with the naked eye. Therefore it was linked to the ancient gods of war and even today astrologists still attribute strong animal instincts to it such as anger, lust and energy. 

Of course, this is all nonsense.

Mars's reddish colour derives from the significant iron content of the dust on its surface, which in a very distant past reacted with oxygen. So it would be correct to say that Mars is... rusted. 

For astronomy enthusiasts on Earth, Mars is not an easy planet to observe because the faint details on its surface drown in its significant brightness. It's like looking at a seriously overexposed photograph. Fortunately, looking with both eyes in stead of one reduces this effect and I didn't have a lot of difficulties distinguishing the surprising details you can see on my sketch.

Monday 6 August 2018

Lunar eclipse

A lunar eclipse is always a wonderful event and there's little that I can add to what other, more talented bloggers and writers have said about last month's "blood Moon". Suffice to show you my impression of how my wife and I observed it through my Nexus 100 binoculars at 24x, just when the Moon was about to leave the Earth's shadow...

Here's the original sketch: