Spacecraft Cassini gets an extra two years

It's almost four years since Cassini arrived at Saturn and sent back those beautiful images of the giant planet and its moons. Since then it has been sending back vast amounts of valuable data, a truly successful space mission. And now NASA have just announced their plans to extend its mission by two years to include many more orbits of Saturn and fly-bys of Titan and Enceladus.

If it completes the next two years of its mission Cassini will have been sending back data for six years, still not quite as long as the seven years it took to reach Saturn. Contrast this with the few days it takes to get to our moon and back.

Bees need your help

You may have seen recent reports of the viral threats that are affecting honey bees, and the possibility that the UK honey bee population will be devastated. This will have an effect on many crops which rely on bees for pollination, without which the plants will fail to set seed and produce fruit.

Red Mason Bees which occur in the wild are also important pollinators and are sometimes used in commercial greenhouses. These fascinating insects are worth encouraging into the garden. They are not aggressive, in fact the male does not have a sting and the female, who has a very weak sting, will only use it if handled roughly, so they are quite safe around children and pets.

They are called mason bees because they build a tiny wall to close off the holes in which they lay their eggs. One of the best ways to encourage them is to provide nesting sites which can also be used by other useful garden insects. You can find these in our online catalogue in the bee section 

Aurora Borealis

Dave Ward, one of our regular customers, brought in some beautiful photos he took on a recent trip to Tromso to see the northern lights. Despite the sunspot minimum we're currently passing through there was a lot of auroral activity which Dave watched from a very dark site. He went by air and recommends the trip to anyone who wants to see the aurora but only has time to fit in a short visit.

BAA Instruments and Imaging Section Meeting

The BAA I&I Section are holding a one-day meeting at Wootton near Northampton on Saturday 10th May 2008. Speakers include Allan Chapman and David Whitehouse and it looks like being a very interesting day in a good venue. The cost is only 3 pounds so if you fancy hearing a bit of history and learning how a contemporary astronomer refurbished his own observatory then why not go along. Details are on the BAA Web Site and it is open to everyone, not just BAA members. I shall be in Lourdes on that day otherwise I would definitely attend. (If you go to the website please ignore the 'meetings' button and scroll down for details.)

Scope Covers

Our new scope cover has proved very popular and demand has been higher than we expected. I suppose we shouldn't be too surprised because it's a very good product and much cheaper than most other scope covers. It can be used for other things as well. I used one to cover a stack of six garden chairs to protect them from the weather and make the garden look tidier. It's been in place all winter as part of the testing we carried out and it performed extremely well. If you would like one you can order it from our online catalogue or pick one up at the showroom.

Green Witch Talks

We often get asked to give talks to local societies and other organisations and are always happy to oblige, so I thought I would mention it in the newsletter in case you are looking for a speaker. Lee can speak on a wide range of astronomy topics, from a basic introduction for beginners through to advanced use of imaging devices. Ralph does a very useful and practical session on using a webcam for imaging the moon and planets. I like to speak on the Isaac Newton Group of Telescopes on La Palma as I spent many years helping to build and run it. The talk can be tailored to astronomers, engineers or a lay audience.

If you are interested in having one of us give a talk then please call us on 01954 211288.

Green Witch Videos

We are experimenting with short video clips to help illustrate some of our products and have placed a couple on our web site at http://videos.green-witch.com/ (note there is no www) The plan is to choose a method of making and presenting video clips that is practical for our small number of staff but which is useful for our customers. I would appreciate any feedback on the first videos. These are not streamed, ie, the whole file downloads and is then played by your default media player. Hope you enjoy them.

Lunar Eclipse on Saturday August 16th 2008

There is only one more lunar eclipse this year but because it occurs at a convenient time during the evening we've decided to hold a lunar party at Green Witch. The eclipse starts before the moon rises in the early evening but will reach maximum just after ten o'clock when over 80% of the moon will be in the umbra, the darkest part of the Earth's shadow.

Amongst other things we will have presentations on the moon which will explain Saros Cycles and other related phenomena; please put the date in your diary now and look out for further details nearer the time.

Looking South at 10 pm (from Cambridge in the UK)

Saturn and Regulus make a fine couple just to the right of our meridian and they are only two and a quarter degrees apart. They are still closing as Saturn continues its retrograde motion but it has almost reached its closest point and will soon start to move away from Regulus again.

Using Saturn and Regulus as an unmistakable starting point to identify the backwards question mark of Leo's head, you should be able to find the three stars that mark his hind quarters, including Delta Leonis which I want to take a closer look at. This is the star that marks Leo's back or hips and it is very close to the meridian at ten o'clock.

Delta Leonis is a main sequence star, ie one that is powered by fusing hydrogen to form heavier elements, mainly helium. It is very similar to our Sun in this respect but because it is more than twice the mass of the Sun it is burning up its nuclear fuel at a much faster rate. It is believed to be about 750 million years old and to have less than that to go before it leaves the main sequence and enters the next phase of its life. Compare this with the Sun which is about half way through its nine or ten billion years on the main sequence.

Delta Leonis and our Sun will share a similar fate when their hydrogen runs out. They will begin to burn helium and will expand into red or orange giant stars. After that they will become planetary nebulae and shed mass by blowing off shells of material before shrinking to become white dwarves. As mentioned above Delta Leonis will just get there quicker than the Sun, it will also shine more brightly and is currently about 24 times the luminocity of the Sun.

It is also known as Zosma or Duhr (sometimes spelt Dhur) and is around 58 lightyears from Earth. It is getting closer to us by 20 km every second and is rotating very fast, about 90 times faster than the Sun and taking less than half an earth day to complete one revolution. It forms part of a group of stars called the Ursa Major Stream, all of which appear to be moving in a common direction through space.

So when you look up at this point of light in the sky try to imagine it as it really is. About twice the diameter of our Sun, twice the mass and spinning 90 times as fast. 24 times as luminous and living life in the fast lane. We can't see its shape but it will have 'middle-age spread' due to the high speed of rotation. You can also wonder what its relationship is to the other stars, including Sirius, that make up the Ursa Major Stream. If you come up with an answer let me know because I don't think anyone else has a good explanation.

And finally...

There's a report on the New Scientiest web site that says the Earth might meet a catastrophic end well before the Sun expands to become a red giant in four or five billion years. Researchers have tried to predict whether the planets will continue in their current orbits or whether interactions between them will lead to more chaotic motion. They claim that there is a one or two percent chance that things will become chaotic and it's even possible that Earth and Mars will collide. It's thought that a mars-sized object once collided with the Earth to produce the Moon and a similar collision in the future would certainly destroy all life on Earth.

The calculations behind these predictions are extremely difficult to carry out and tiny changes in the starting conditions make a big difference, rather like the proverbial butterfly flapping its wings and creating a tropical hurricane. But don't worry yet. Although the researchers admit to problems with their long-term predictions they are confident that things will continue as they are for at least 40 million years.

Clear Skies and Best Wishes

Neil

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