This is a one minute exposure of the sky taken from the car park at Hauxley Nature Reserve, the meeting place of NASTRO. It was taken with my Nikon D80 at ISO1600 and a fisheye lens. The major sources of light pollution are towards the south and west and is the combined lights of Ashington, Blyth, Cramlington and Newcastle. Towards the west and southwest are the villages of Broomhill, Togston, Red Row and Hadston. Lights from a caravan park shine through the trees to the east. The town of Amble is towards the north.
It actually looks a lot darker in reality than the camera suggests! The Milky Way is very prominent at this time of the year and the light pollution only seems to be a problem near the horizon. But the camera doesn't lie. The atmosphere scatters the yellow/orange light from towns and cities very effectively and long exposure images rapidly develop an orange background.
NASTRO was given a little bit of funding earlier in the year to purchase a Sky Quality Meter to measure sky brightness. The average of three readings last night was 20.9 magnitudes per square arcsecond. For a feel of what this is like compared to other locations see the Bortle Scale descriptions; Hauxley Nature reserve corresponds roughly to Class 4 "Rural/Suburban transition".
I got some pictures of the comet earlier in the year with an 80 mm refractor while it was still far from the Sun.
I really had to stretch the contrast with that second picture because the sky was not completely dark and ISON was still very faint. In the months since I took that second pictures ISON has brightened - but only a little. You'll still need a telescope to see ISON until perhaps early November.
September to late November
ISON is observable in the eastern sky before sunrise for all of this period.
The chart below shows the altitude and azimuth of the comet at the start of nautical twilight (when the Sun is 12 degrees below the horizon - about one and half hours before sunrise in the UK).
The magnitude estimates are to be taken with a pinch of salt. It might be visible with binoculars by early November - but that's just an educated guess at this time.
October and early November, when the moon is out of the way, are clearly the best times for UK astronomers to view the comet before perihelion. The comet will be at a decent altitude above the horizon and getting brighter each morning.
I've generated a finderchart for ISON using my favourite software: SkyTools 3. It will give you an idea of the path taken through the constellations, but to actually find the comet you'll need to feed the exact coordinates of the comet to your GoTo telescope. Or learn to star-hop from more detailed charts (at least until the comet becomes bright enough to see more easily in November).
ISON and Mars (and Regulus)
ISON is close to the planet Mars in the pre-dawn sky for all of September and October. ISON's close approach to Mars is more than just a line of sight effect. On October 1st ISON will pass about 0.07 AU (6.5 million miles) from Mars. That's close enough for the numerous orbiters and landers to get images of it. They'll hopefully provide clues as to whether or not the nucleus of ISON is big enough to survive its encounter with the Sun.
Although physically, they are further apart, Mars and ISON will appear much closer together in the sky on the morning of October 18th ISON will be less than one degree from the planet in the sky. This might make an interesting picture if the weather is good!
The picture below shows the position of ISON, Mars and Regulus (the brightest star in the constellation Leo) on the morning of October 15th.
Two Autumn Comets: ISON and Encke
Comet ISON will be joined in the morning sky by another reasonably bright comet this autumn. The short period Comet 2P Encke, which rounds the Sun every 3.3 years, will pass close to ISON in the sky.
Comet Encke couldn't be more different from ISON! Encke's comet been observed more than any other comet in history. Encke has likely been around for thousands of years and has lost much of its volatile surface material. Although it can approach the Earth quite closely, it is never a particularly bright comet. There are suggestions that the Encke's comet was responsible for the Tunguska event in June 1908. Material from this comet intersects the Earth's orbit each November. In fact it has spread so much over the centuries that it takes the Earth most of November to pass through it; they are the origin of the complex Taurid meteor showers each year.
I'm going off on a tangent.,,,
Comets ISON and Encke will share the same part of the sky in November as they both pass through the constellation Virgo. They should be of similar brightness and visible with binoculars in the sky before dawn.
The final chart below shows the tracks of the two comets through the constellation Virgo. Magnitude estimates are very approximate, but Encke is likely to be the brighter of the two.
Interesting to see that ISON passes very close - just 18 arcminutes - from Spica, the brightest star in Virgo on November 18th at 0200UT. This is shortly before ISON rises but the separation will only have increased a few arcminutes by the time the star and comet are visible in the UK. Spica may well be shining through the coma of the comet!
Ok, that's it for now. Visit my blog again for updates on the progress of the comet and hopefully some pictures. Good luck and clear skies if you're trying to observe ISON this autumn :-)
Solar eclipses, when the moon passes in font of the sun, are quantified by a number called the magnitude.
The magnitude of a solar eclipse is defined to be the maximum fraction of the solar diameter covered by the moon. The app below shows an eclipse with a magnitude of 0.5. That means the moon covers half the diameter of the Sun.
So how much of the Sun's area is obscured? Clearly it's less than half...and it in this case turns out to be about 39%.
Move the slider to change the position of the moon's centre and you'll see the magnitude and the obscuration change.
The Earth has an elliptical orbit around the Sun and the moon has an elliptical orbit around the Earth. Those facts mean that the apparent sizes of the Sun and Moon look different from eclipse to eclipse. It also means that sometimes the Moon can look bigger than the Sun (so a total eclipse may be possible) or it can appear smaller (so it cannot completely hide the Sun and an annular eclipse may be possible). Realistic values for the Sun radius in this app are between 0.98 and 1.02. Typical values for lunar radius are 0.92 to 1.08.
I included a greater range of values for the Sun and Moon radii because they might be used to represent eclipses of other objects; moons around other planets, or exosolar planets passing in front of their parent stars.
The obscuration calculation uses simple area formulae for circular sectors and triangles. More details of how the magnitude and obscuration are calculated are shown below.
It's empty. For the last few months the image has shown noctilucent cloud coverage over the poles. NLCs form in the summer months when, as strange as it sounds, the mesosphere is cold enough to allow it.
I saw these noctilucent clouds on lots of evenings over the past few months (and in most summers that I can recall). Some of the pictures I took can be found here, here and here.
I made a movie of all the daily daisies during this NLC season and assembled a short movie.
The data was assembled from the website of the AIM-CIPS instrument. You can see that the coverage increases from nothing in May, to a maximum in early July and then decreasing to nothing again in August.
As we approach the end of the summer the mesosphere begins to warm again the clouds disappear. No more NLCs until the next season begins sometime near the end of May 2014.
Venus is almost as far as it can be from the Sun in the sky. But in the UK Venus is not well placed after sunset. The best time to observe Venus through a telescope from here is actually through the day when the planet is high above the horizon.
This image was made from a stack of 50 frames --- the best 10% of a whole series taken with the QHY5 Mono camera at prime focus of my 8 inch LX10. The atmospheric seeing was terrible - it was early afternoon and hot; the air was very turbulent and it was like looking at the planet through rippling water.
Nevertheless the gibbous phase of the planet - between half and full - is evident. SkyMap Pro gives the phase as 77%. Venus is the brightest planet and it was easily visible through the finderscope. The angular diameter of Venus was 14 arcseconds. That's how big a £1 coin would look from a distance of 330 metres (1,083 feet). Not surprisingly there are no details visible on the planet. Venus is wrapped up in a dense, cloudy atmosphere and even on a really good day it takes a lot of filtering and processing to bring out any kind of detail in those clouds.
This is a quick follow up to my previous post about the nova in Delphinus. I took some pictures on the evening of August 16th when the nova was close to peak brightness. Here is a widefield view showing the nova and surrounding constellations.
That picture was taken with my Nikon D80 at ISO1600 with the zoom lens at 18mm.
I put the same camera on a small telescope (80mm refractor) on a mount capable of tracking the sky. A series of 2 minute images taken at ISO800 were stacked to given this close-up shot. The horizontal red-line in the above image seems to connect two pairs of stars (including the nova). The orientation is slightly different but you can see the two pairs below:
The nova is the bright star at the centre of the picture.
As I said in a previous post the nova is a tiny white-dwarf star which has been fed gaseous material from a companion star. A point is reached where the pressure and temperature of the gas dropped onto the white dwarf becomes so high that a runaway nuclear reaction kicks off and the shell of material detonates and the nova is born.
I made this picture showing the nuclear detonation of the material around the white-dwarf star.
The nova remains visible in the sky, although the full moon has made seeing it without binoculars or telescopes difficult over the last few days (and for me, the weather has been terrible!)
A new star has appeared in the sky. Well, not really. It was there all along but it suddenly flared in brightness and caught the attention of an astronomer on August 14th. Astronomers call it Nova Delphini 2013.
A nova is a stellar outburst but on a less violent scale than a supernova. Unlike a supernova, a nova does not destroy the star.
Novae occur in binary systems where one of the pair of stars is a hot, compact object called a white-dwarf. The other star in the system (maybe a main sequence or red giant star) orbits close enough for material to drawn into an accretion disk around the white dwarf. The material (hydrogen and helium mostly) adds mass to the surface of the white dwarf and increases the temperature and pressure until a runaway nuclear reaction begins. Some of the energy released is in the form of light (the nova in this case brightened by 25,000 times than the progenitor binary system) and intense stellar winds - strong enough to blow away the deposited material so that the reaction eventually grinds to a halt. The flare in brightness is followed by a decay to normality.
The nature of the binary system means that the process may repeat after intervals of decades, centuries or many millennia.
Novae can recur if we wait long enough.
Finding the nova
The nova has the following coordinates:
Right Ascension 20h 23m 30.1s
Declination: +20° 46' 04"
That puts it in a very convenient part of the sky for UK astronomers at this time of the year. Here's a star chart showing the location of the nova in relation to bright stars of the Summer Triangle.
The nova is within the borders of Delphinus (hence the name Nova Delphini 2013) and the borders of Vulpecula and Sagitta. It's probably easiest to locate it visually using Sagitta as a starting point.
I put a couple of green arrows on to show how to star-hop to it from the relatively easy-to-see shape of Sagitta. Follow the shaft of the arrow - it almost points straight to the nova. in binoculars, there are only a couple of stars nearby to rival the nova in brightness.
The nova was about 6th magnitude when it was discovered. That means it was barely visible to the naked eye from darksky site. In a few days it had doubled in brightness and is currently shining at 5th magnitude. That makes it one of the brightest novae of recent years and an easy target for binoculars and small telescopes.
This is the best time of the year to appreciate the crowded starfields of the Milky Way. Until last week Nova Del 2013 was white dwarf lost among the countless millions of stars beyond the reach of all but the biggest amateur telescopes. For now it stands out from the crowd.
Sat in the garden with a cup of coffee watching the Perseids zip across the sky. I saw a couple of dozen - it averaged out at about one per minute. The camera was taking one minute exposures of the whole sky. The best picture I got showed a Perseid shooting down the Milky Way as it emerged from behind a cloud.
The shower is building towards a maximum this evening and forecast is good. I'd like to get another meteor picture without a pesky cloud in the way.
I was torn between leaving the camera taking whole sky pictures and getting a shot of some deepsky object through the telescope. The DSO won and I took about eight 3 minute exposures of the Veil Nebula.
A star detonated here between five and eight thousand years ago. The gaseous wreckage continues to expand into the interstellar medium, carrying heavy elements which might get incorporated into a future generation of star formation and perhaps planets capable of supporting life. The Veil Nebula covers a huge area of the sky; there's a clear 2.5 degrees between the east and west portions of the nebula. That's big enough to fit more than 5 full-moons edge to edge!
The only big DSO left that I want to photograph is the Heart Nebula in Cassiopeia; hopefully I'll get a chance tonight with a clear sky.
Dr Adrian Jannetta
Guitar strummin' explorer of the universe. Mild mannered maths teacher by day and astronomer by night.