Category : Cambridge Astronomy Association

CAA Talk – Gamma-ray Bursts

The monthly Cambridge Astronomy Association talk was entitled “Gamma-ray bursts at probes of the distant Universe” by Professor Nial Tanvir.

Nial gained his PhD on the extragalactic distance scale at the University of Durham in 1992, and then came to the Institute of Astronomy where he was a postdoc. He became a lecturer at the University of Hertfordshire in 1999, and he became a professor at the University of Leicester in 2006.

Gamma-ray bursts are the most luminous events known in the Universe and can be detected at great distances. Nial described how GRBs are being used to study the first generations of stars and galaxies, and to consider prospects for pushing these studies further in the future. He also give an update on the recent record-breaking GRB 080319B, which is by far the most distant “naked-eye” source ever found.

The talk was very in-depth, but very interesting as I had seen information on how the Gamma Ray bursts are recorded and people are notified via email or SMS text message that a Gamma Ray burst has occured.  I think there was a Sky at Night program about it.

We were told how Hubble in the 1920’s proved that spiral nebulae were external galaxies to the milky way at great distances. Hubble also discovered how the entire universe seems to be expanding.

I discovered that light travels at 300,000 km per second. We were also shown the different types of wavelengths in the electromagnetic wavelength.  These are radio waves, microwaves, infrared, visible light, ultraviolet light, x-rays and gamma rays.

We also learnt the basics of how the current universe was formed in this order:

  • Big Bang (0)
  • Inflation (10-32 seconds)
  • Quark Soup (1 second)
  • Big Freeze Out (300,000 years)
  • Parting Company (1 billion years)
  • First Galaxies (12-15 billion years)
  • Modern Universe

Gamma Ray Bursts (GRBs) are detected by satellites, the main one being the SWIFT satellite. 

080319B was an extremely intense GRB with the brightest visible afterglow ever (at 5th magnitude, bright enough to see with the naked eye). It is the most energetic event detected by the Swift satellite so far and the most luminous optical source ever seen.

Overall I learnt that the Gamma Ray bursts probably originate from distant galaxies, which are difficult to see via optical systems.  The main worry is that a nearby gamma ray burst could possibly cause mass extinctions on Earth.

Introduction to Astronomy – Week 4

Week 4 of the Introduction to Astronomy course at the IOA in Cambridge saw us having a talk from Carolin Crawford entitled “The Stars, Gas and Dust of the Milky Way”.

Carolin’s talk was one of the most interesting and complicated that we have had so far on the course.  Carolin’s talk really centered around the gas, dust and dark matter that exists in our universe.

The talk began by describing the size of our universe and our place in it. It was described to us that our bulge in our universe is 6kpc wide (kiloparsec) which is about 19.5 lightyears. With the stellar disc being about 30kpc, the outer stellar halo being 50kpc and the dark matter halo being outside of this. The dark matter halo makes up 90% of our galaxy by mass. 

It was also pointed out that hydrogen is the most common element in our solar system.

We were shown that we are located in the Orion arm of the galaxy between the Sagittarius and Perseus arm.

It was good to be shown some amazing images of nebulae from the Hubble telescope, as it allowed me to record some names of nebulae worth looking out for, which included Cats Eye Nebula, Eagle Nebula, Rosette Nebula and the Iris Nebula.

At the end of the talk we went to view the moon through another of the Institutes Telescopes.  This time it was the 36 inch telescope.

The 36 Inch Telescope

36 Inch Telescope at the Institute of Astronomy in Cambridge UKThe 36 inch telescope was built in 1951-55 by the now-defunct firm of Sir Howard Grubb, Parsons & Co. at Newcastle-upon Tyne. It replaced a much older telescope of the same aperture, which was brought to Cambridge from South Kensington when the Solar Physics Observatory moved there in 1913. That telescope was returned to its owners (The Science Museum) before the new one was installed; the Director of the Observatories at the time (Professor R.O. Redman), who in his youth had made substantial use of the old telescope, always averred that it should never have left the Museum!

The 36-inch, which is thought to be the largest telescope in the country, has three possible focal stations. There is a prime focus with a focal ratio of f/4.5; the primary mirror is a paraboloid, so no corrector is needed to obtain good images on the optical axis. In practice the prime focus has been little used: the telescope is large enough to make access to the focus difficult from the side of the tube. The other possible foci are coude, with a choice of two focal ratios, f/18 and f/30. The coude arrangement is unusual inasmuch as the light beam is directed UP the polar axis rather than downwards: that permits the shorter focal ratio to be exceptionally short for a coude, and results in a focus at a level near to that of the telescope, which is somewhat convenient for a lone observer who needs to operate both the telescope and whatever auxiliary equipment is placed at the focus.

On the other hand, the arrangement lacks part of the advantage of a conventional coude focus, which is often in a basement that enjoys good passive thermal stability (and, from the point of view of the observer personally, protection from wind and extremes of cold!).

Until recently the f/18 focus has been the favoured option, but new equipment that for the first time utilizes the f/30 arrangement has now been brought into use.

The f/30 focus is just within the dome, high up to the north of the telescope, and its use involves a further reflection. In the present application, that reflection takes place close to the focus, and the beam is turned vertically downwards by successive internal reflections within two right-angle quartz prisms cemented together.

The initial image is re-imaged at a focal ratio of f/14.5 at the position required for the auxiliary equipment. A simple plano-convex quartz field lens is cemented to the exit face of the quartz-prism assembly to image the telescope aperture upon the re-imaging lens.

In the early years of its operation, the telescope was used to send starlight into a spectrometer where the light intensities in several wavelength regions. which were accurately defined by masks in the focal plane of the spectrum, could be inter-compared.

The view through this scope was one of the moons craters, although it was not exactly clear,  I think a view of the full moon would have looked more impressive.

The telescope itself is very impressive and very large, it sits on a classic Alt type mount just like my LX200 but this also have a fixed concrete wedge underneath it as well.  The telescope itself does track, but unfortunately most of the domes require manual rotation.

Introduction to Astronomy – Week 3

This week at the Institute of Astronomy in Cambridge we had a talk by Ken Day entitled “A Cook’s Tour of the Solar System” as part of the Introduction of Astronomy course I am partaking in via the Cambridge Astronomy Association.

Ken took us through all of the planets in the solar system, plus comets and asteroids. He gave explanations about each object in the solar system and backed up each item with some great full colour images in his presentation.

I picked up a new useful facts such as:

  • The word “Planet” means wanderer in Greek.
  • The Sun is 109 times the diameter of the Earth.
  • Venera 9 the Russian probe to Venus in 1975 only lasted 23 minutes once it landed due to the harsh surface environment.
  • Olympus Mons is the largest volcano in the Solar System which is on Mars.
  • There are dark “spokes” in Saturn’s rings – something that I did not know.

There was no trip out to any of the IOA telescopes tonight, a bit of a shame as it was a clear night, but instead we were joined by Green Witch the astronomy retailers from near Cambridge.  They bought a few items with them including Philip’s astronomy book, some binoculars and a Skywatcher telescope and some eyepieces.  They also handed out flyer’s offering us 5% off anything we purchased.

Green Witch set up a Celestron NexStar 5 telescope outside and they gave us the chance to view Mercury and the Moon. Everybody rushed outside after the talk so there was a queue to view Mercury, which everybody wanted to see.

Whilst the NexStar was being re-aligned on Mercury (the scope seemed to drift a lot, and not track that well) it was strange to see how similar the menu options were on the Celestron to the Meade, as I have never used or really seen a Celestron NexStar before. After two cups of coffee it was time to go home.

Introduction to Astronomy – Week 2

Week 2 of the Introduction to Astronomy course was presented by Peter Howell entitled “Sunshine and Green Cheese”. Peters talk covered details on the Moon and the Sun.

Peter started by talking about the Sun, and gave a great talk on every aspect of the Sun, including information that sunspots appear in magnetic pairs. Also that charged particles from the Sun give rise to the Northern and Southern lights. It was also interesting to hear that a supernova 10 billion years ago produced gold.

Peter then discussed in depth about the various stages of the moon, and why First Quarter is called what it is, and he pointed out all the Apollo landing sites on the Moon.  Peter also showed images of interesting areas of the Moon to look at, including Schroter’s Valley, Rupes Recta fault line and the Hadley Rille.

Peter handed out paper moon maps as well as sheets in order to allow you to construct your own sun dial (diptisch dial). It was very interesting to find out that the equation of time varies heavily between summer and winter, indicating that the Earth rotates at different speeds through out the year.

Cambridge Observatory BuildingAfter the talk was over and we had tea, we ventured out to the Institute of Astronomy’s outside Observatory building which houses the library. The library room holds a number of very old and interesting astronomy and cosmology books together with the latest astronomy journals and magazines.

Whilst in the library room we managed to see slides taken between 1945 and 1985 by the Schmidt telescope. 

The Schmidt instrument was built in 1952 by Grubb-Parsons of Newcastle-upon-Tyne and replaced an older telescope in the existing dome, which had been made by T. Cooke & Sons Ltd. of London & York at the time of the move of the Solar Physics Observatory from South Kensington to Cambridge.

It is a `Classical Schmidt’ – the simplest and most efficient form of the ingenious wide-field camera invented in 1930 by Bernhard Schmidt of Hamburg Observatory. Light from the sky falls upon a 61 cm (24-inch) mirror with a spherical reflecting surface, at the bottom of the tube. It is reflected to a focus in the centre of the tube and half-way up it, 163 cm (64 inches) from the primary mirror. At the focus a photographic plate P 15 cm (6 inches) in diameter, which must be bent to fit a curved surface, records the star images in an area of sky 5 degrees in diameter. (The full Moon is half a degree in diameter.)

Below are some images I took with my mobile phone that were produced by the Schmidt Camera of Halley’s Comet in 1986 and another part of the cosmos.

Halleys Comet Image from Schmidt Telescope 1986 Image from Schmidt Telescope at Institute of Astronomy Cambridge

Introduction to Astronomy – Week 1

Tonight I attended the first night of the Cambridge Astronomy Associations Introduction To Astronomy course which was held at the Institute of Astronomy in Cambridge.

Tonights talk was entitled “Things that go bump in the night” by Brian Lister. Brian took us through the basics of the solar system with some very interesting images of various craters. This included the Mead crate on Venus which is 280km wide, as well we the 65km wide crater in Quebec and the 200km Hellas Basin crater on Mars. There were also images of the Abulfeda crater chains on the moon.

Brian also conducted a couple of experiments, one was to demonstrate how stars explode, by inflating and exploding a balloon in a cardboard box full of packing material. See the video of this below, the experiment did not quite work as expected, or as I expected anyway.

After the talk was over and we had our tea and biscuits we headed out to one of the telescopes on the Cambridge site to view Saturn.

Cambridge Institute of Astronomy Northumberland Telescope DomeWe used the Northumberland Equatorial University Observatory which was built in 1838. “The Northumberland” is the only remaining large instrument from the early days of the University Observatory. For many years it was one of the world’s largest refracting telescopes.

The main structure was built by the engineers Ransomes of Ipswich, and the fine mechanical work by the London Instrument makers Troughton and Simms.

The polar axis frame and the telescope tube are made of Norwegian fir. The original Cauchoix lens is not used anymore and the optics are now up to date, with a 12 inch aperture visual achromatic doublet designed by Dr R.V. Willstrop of the Institute and it was constructed by the local firm A.E. Optics Ltd, installed to mark the 150th anniversary of the telescope.

The steel dome covering the telescope was made in 1932, which was a replacement for the original 96 year old wood structure. The telescope was last used in a regular Observatory research programme for the micrometrical measurement of double stars in the 1930s. Although the telescope is still used for visual observations by members of the University Astronomical Society and for public observing at the Institute of Astronomy during the winter months.  So it’s great to see it still being used after 150 years.

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