Green Witch

 Newsletter 38

  • International Space Station and Jules Verne
  • Iridium Flares and Other Satellites
  • Imaging Venus
  • Starlight
  • Kelling Spring Sky Camp
  • Cassini - preliminary results from the close encounter with Enceladus
  • Arcturus
  • Looking South at 10 pm from Cambridge, UK
  • And finally...


Newsletter 38 - 31st March 2008

 International Space Station and Jules Verne

The International Space Station (ISS) orbits are now conveniently positioned for viewing in our UK evening skies. The European Space Agency's resupply vessel, Jules Verne is manouvering close to the ISS for a planned docking on April 3rd which will add interest to any observations.

There are two visible passes most evenings for the next week and you can get times and directions for your location from the excellent web site at  You need to select your location if you aren't already registered with the site. If your search for passes doesn't give you any then check that your location is set correctly. You can do this easily by choosing the 'select from database' option. Choose your country, search on your town of village name then select the correct option from the search results.

There will be two passes tomorrow evening when we plan to have our April 1st Star Party (to which you are invited - just turn up, there is no need to book). The first starts at 19:57:04 so we will bring forward the start of the party to 7:45 pm. The second pass starts at 21:31:53 and each lasts between two and three minutes. Both are bright; the first is magnitude -1.9 and the second is even brighter at -2.5.

The best way to see the ISS is to use your naked eye and look towards the south-western horizon for the first pass and the western horizon for the second. Once you spot the ISS you can use binoculars to follow it. Experienced observers with computer-controlled telescopes might like to try tracking it.

My thanks to Dave Eagle and Peter Ashwell from Bedford Astronomical Society for drawing my attention to this.

Iridium Flares and Other Satellites

While visiting the Heavens Above site why not make note of Iridium flare predictions and other bright satellites. Iridium flares are caused by sunlight reflected from the Main Mission Antennae on a fleet of communications satellites in low-earth orbit (around 780 km). It is sometimes possible to spot the satellite before the flare and to watch it brighten and fade again as the sunlight glints off an antenna.

For more information on observing Iridium satellites see the help page on Heavens Above

Predictions are given for other bright satellites as well. For example, tonight there are nine satellites brighter than magnitude 3.5 (easily seen in a clear sky) that are visible from Green Witch between 9 pm and 11:10 pm local time.

Imaging Venus

In the last newsletter I suggested getting ready to take images of Venus in the late summer. The European Space Agency is encouraging amateur astronomers to do this to supplement observations taken with the Venus Express space craft.

If you like the idea of contributing to a space mission then visit ESA's VAOP Page  for advice on equipment, observing techniques and how to submit your images. Take a look at the ground-based archive to see some of the images submitted so far. Click on an image for details of the observer and equipment used. At the time of writing the 8th and 9th most active imagers had only one image accepted so there is lots of potential for you to make an impact. If your image is used in a scientific paper you will receive credit for it.


If you've seen April's edition of Astronomy Now you may have noticed the first issue of Starlight, an 8-page pullout designed for children between the ages of ten and fourteen. If you have children in this age range and don't already subscribe to Astronomy Now you might like to consider doing so. If you're already a subscriber and don't have children who would appreciate it, why not pass Starlight on to a neighbour. You might ignite a lifelong interest and just think how good that would make you feel.

Kelling Spring Sky Camp

The Spring Sky Camp will be held at Kelling Heath from Thursday 3rd to Sunday 6th April. Wendy and Ralph plan to be there on Saturday so please give them a call if you would like them to bring anything in particular. The Spring Sky Camp is a less formal affair than the Autumn Camp and you can find details here.

Cassini - preliminary results from the close encounter with Enceladus

It appears that Enceladus is warmer than expected and the composition of its geysers resembles that of comets. These are two of the first discoveries from the recent fly-bys prompting scientists to get excited about the possibility of liquid water existing below the surface together with organic chemicals and warmth. If there is liquid water then the chances of finding some form of life increase dramatically.


Last night the sky was quite clear where I live and as I browsed the sky Arcturus seemed to be much redder than I remember. I don't think it has changed in any way so assume the conditions and my eyes were good for seeing colour. Arcturus is a red giant star with a mass thought to be between one and one and a half times the Sun's mass. It is thus a good example of what the Sun is likely to become as it nears the end of its life.

Arcturus is the third brightest star in the night sky although it appears to be the fourth as the close binary pair of Alpha Centauri look like a single star that is brighter. Arcturus is the brightest star in the northern hemisphere and the second brightest star we can see from the UK after Sirius (which is south of the celestial equator).

It is in the constellation of Bootes and it is easy to find by following the arc of the plough's handle. The name derives from ancient greek and means 'Bear Guard' being close to the Great and Little Bears.

During the commissioning phase of the William Herschel Telescope on La Palma George Isaacs from Birmingham University observed Artcturus for three weeks with a very sensitive red-shift monitor to try to detect a wobble that would indicate the presence of an extra-solar planet. No such planets had been discovered at that time and George's observations only set an upper limit for the size of a planet, should one exist in orbit around Arcturus.

In 1933 the Chicago World's Fair was opened by light from Arcturus. At that time it was thought that the light would have left Arcturus at the time of the previous Chicago World's Fair in 1893. Current estimates gives its distance as 36.7 lightyears so it would have started its journey in 1896 but it was a neat idea. Perhaps we should link Earthly events more closely with the stars to remind city dwellers that they are there.

Looking South at 10 pm from Cambridge, UK

Because of the change to BST the sky appears not to have moved on since the last newsletter so I'll just mention one thing for you to look at. Saturn is very close to Regulus in Leo and the two make a fine pair that is easy to identify. At present Saturn is undergoing retrograde motion, ie it appears to be moving westwards relative to the stars and is getting closer to Regulus. This apparent motion is due to our point of view moving with the Earth.

At its closest, Saturn will be just over two degrees from Regulus then will move away from it as it continues its normally eastwards motion. Why not watch it closely throughout April and see if you can detect when it changes direction. You can always check your answer with a program such as SkyMap Pro afterwards.

And Finally...

I was in the Alps in Southern France last week expecting clear dark skies at night as we had beautiful blue skies during the day. I was disappointed that the faintest stars I could see were between third and fourth magnitude. It made me realise just how dark and clear the skies are in Arizona. There I can see the Milky Way from horizon to horizon without waiting for my eyes to dark adapt. If you haven't experienced this why not book a holiday at the Green Witch house. The exchange rate makes it very cost-effective and there is a lot more to do besides astronomy. Take a look at our web site at to see if it's for you.

Clear Skies and Best Wishes



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