The North Devon Astronomical Society reports on the night sky in North Devon.
In August the nights begin to noticeably draw in again. The beginning of the month the Sun sets at 9:02pm but does not get fully dark until about 11:50pm, but by the end of the month the Sun sets at 8:04pm with full darkness by about 10:10
The Planets
Mercury is at greatest eastern elongation on the 6th, but despite this it is poorly placed and will be difficult to spot.
Venus, Mars and Saturn are all close to each other early in the month being at their closest to each other on the 7th and 8th when they all are just within 5° of each other. They will be low down towards the western horizon as the Sun sets. At magnitude -4 Venus should be fairly easy to spot, but Saturn and Mars will not be so easy as they are all only seen in twilight and setting before full darkness descends upon us.
Jupiter and Uranus are also close to each other remaining within 4˚ of each other all month (next month will see them within 1° of each other). They are well placed in the sky, but reach their highest in the sky around 1:30am. They remain in Pisces this month close to the border of Aquarius.
Saturn is still easily visible in the evening sky. The rings are still not very ‘open’ having had a ring plane crossing just last September.
Neptune is well placed this month in the constellation Aquarius at the start of the month, but passing into Capricornus by the end.
The Moon
Last Quarter 3rd August
New Moon 10th August
First Quarter 16th August
Full Moon 24th August
Helium is the second most common element in the Universe making up about 24% of normal matter by mass. Hydrogen makes up about 74%, by far the most common, with all of the other elements (which astronomers refer to as ‘metals’) making up the rest (about 2%). Despite this it is relatively rare on Earth, most having escaped early in our planets formation.
Helium in its natural state is a gas, with a boiling point of -267°C (that’s just 4°C above absolute). It is a ‘noble gas’ which means it is chemically inert, that is it will not bond with other elements apart from in a few exceptional circumstances. Water, for instance, is a molecule consisting of two hydrogen atoms and one oxygen atom chemically bonded. Both of these elements at normal ‘room’ temperatures are gases also.
Helium was in fact first discovered not here on Earth, but in the Sun’s atmosphere during the total solar eclipse of August 18th, 1868. Both Pierre Janssen and Norman Lockyer observed a prominent yellow spectral line in the Sun’s chromosphere. This spectral line, unlike other spectral lines, could not be identified with any known substance at that time, and that it was caused by some unknown solar element. Norman Lockyer named this element helium derived from the Greek word ‘Helios’ meaning sun.
It wasn’t until 1882 that helium was detected on Earth, when Italian physicist Luigi Palmieri found the same spectral line when analyzing the lava of Mount Vesuvius. In 1895 Sir William Ramsay was able to isolate helium in the laboratory.
The vast majority of Helium was ‘manufactured’ by a process of nucleosynthesis during the first moments of the big bang, between the first minute and third minute. It is however being produced at the core of our Sun, as well as many other stars as Hydrogen is fused into Helium. It is this process that keeps them shining as it involves a small amount of mass (about 0.07%) being converted into energy. A lot of energy is produced in this manor as Albert Einstein showed. The energy yielded is E=mc2. There is enough hydrogen in the core of our Sun to keep it shining for another 5 billion years. As the hydrogen runs out in the core, gravity will cause the core to collapse and become even hotter from its present 15 million °C. This is also accompanied by the outer layers expanding and our Sun will become a red giant. Unfortunately Earth will have become far too hot to be habitable at this stage. In the Sun’s case the core will become hot enough, about 100 million °C, for the Helium to fuse into Carbon and some Oxygen and keep it shining for a further billion years. At the end of this in a process not clearly understood the outer layers of our Sun will be thrown of to leave the exposed, but extremely hot core. For a short time (typically 10,000 years) the Sun will be a planetary nebula, but as the layers thrown of expand and disperse into the interstellar medium, all that remains is the hot core of the Sun. It will have become a white dwarf, which is about the same size as our Earth, but with about half a solar mass. An extremely dense object. Over the next billion years or so it will gradually cool off becoming essentially a dead ‘ember’ of the former Sun.
Norman Lockyer went on to establish an observatory here in Devon near Sidmouth. Today it is run by the Norman Lockyer Observatory Society. As well as several telescopes it also has a 60 seater planetarium and hosts public visits to the site. For details visit their website at www.projects.exeter.ac.uk/nlo
Rick Dooley
NDAS Chairman |