Opposition of Saturn

Saturn comes to opposition on the 27th June 2018. Unfortunately for UK observers it doesn’t get very high in the sky being just above the teapot asterism in Sagittarius:

But if you can get to see it, the rings are nice and wide. Note, that Mars is also rising and will reach opposition next month.

Clear skies.

May’s AGM talk

For those of you who missed the AGM, Themos Tsikas tried to squeeze a full length talk into an after tea space. Sadly, time dilation did not work, even though he blue shifted near the end. Perhaps we should try to list the variety of hobbies our members have, besides astronomy. We have now found out that Themos is a very keen sailor.

So he approached his talk from a sailing point of view, and really only hit on the astronomical side at the end.

So, basically you are on a boat on a globe, much of it sea. How do you keep your bearings? Easy if you know what time it is and you can see how high the Sun, Moon, or certain stars are. But that only gives the latitude, not the longitude.

The simplest way is to think of yourself looking up at the sky, hopefully clear(ish) of clouds. At night you should see lots of stars, and these will all be overhead somewhere as seen from Earth. You use a sextant to work out the angle of altitude of certain known stars and imagine a line starting from your position, going round their zenith point and coming back to you. You then wait ten minutes and remeasure. The circle will have changed, unless you happened to pick on Polaris…. If you use the Sun or the Moon, it is not so easy, because of their larger proper motion. You can then work out the circles’ intersection points and that’s where you are. You must also make sure not to crouch or climb onto a higher point to take readings, as that alters the object’s height above the horizon.

Themos did not get as far as the list of navigational stars, of which some have intriguing names (Needless to say, Polaris is not among them.). He did have two sextants, and showed us how to line up the moving mirror (which is linked to the scale via a sliding arm) so that the horizon is lined up with a star, Moon or Sun, thereby giving the altitude.

Please Themos, do bring those lovely gadgets again so we can have another play with them during the tea break. Time ran out on you too soon. At least you had time to show us a quick video of how to use a sextant.

Clear skies

April’s talk

“ALMA”

Neil Philipson is one of those useful people to know, as he clearly has a passion for his topic.  He called himself a designer and telescope seller.

His pet subject is the ALMA setup in Chile, namely the Atacama Large Millimetre Array.

It was completed in 2013 and consists of 66 12metre radio dishes, and these are through a collaboration of Europe, USA and Japan/East Asia.  Europe and the USA provided 25 each, then Japan tacked on another 16 later; these are a grouping of four 12m dishes and 12 seven metre dishes and are called the ‘Compact Array’.  So this is now all called ‘Enhanced ALMA’

He calls it ‘supercomputer astronomy’ and says it’s the largest collection in history.

So why choose microwave collectors?  After all the wavelengths are a thousand times longer than the visual stuff, so the collectors have to be huge, in theory, to get the same resolution as our optical telescopes.  These millimetre and sub millimetre wavelengths radiate from stuff that is close to absolute zero.  This is the oldest stuff in the universe.  You can also include early stage galaxy formation and nebulae which are in the early stages of forming stars.  They radiate in these wavelengths.

Mr Philipson then came onto location.  Our atmosphere blocks most of the radiation at this wavelength so why wasn’t ALMA chucked into space?  (His words). Basically because of the expense, and at 5000m altitude, you can get above most of Earth’s atmosphere and you still get the resolution.

Extravagant suggestions were made for the original location.  After all, you had to have stable, very dry air, and it had to be cool and far away from people.

So, Greenland, the Himalayas and even the South Pole were among the original choices.

The Llano de Chajnantor was finally chosen, 16,500 feet up.  For its trouble, Chile gets 10% observing time.  (Japan gets 15% and Europe and the USA share the rest equally.)

So these 66 dishes have a fairly free rein up there, although they are posted in clumps and have parking pods too.  They are linked by fibre optics to an accuracy of a millionth of a millionth of a second.  (In the same way that we have the very long baseline interferometry of the longer wavelength radio telescopes such as the MERLIN or VLA complexes)  At their biggest separation they have a 16km diameter but can be gathered into a 250m diameter.  At their biggest separation they have a resolution down to 0.004” (arc seconds), which is ten times that of Hubble.  In compact formation, the field of view is 50”, at expanded, it is 1.25″

The dishes are figured to one fortieth of a wavelength of what they’re looking at.  The collecting receivers are in a hole in the middle of each dish and they have to be cooled to 4 kelvin, because the stuff they’re observing is so cold and you don’t want the receivers radiating heat.

Mr Philipson lamented that the achievements of ALMA are not publicised much, but ALMA has been able to see beyond  a very distant galaxy cluster to a time only 200 million years after the Big Bang.  He mentioned the ’Sunyaev-Zel’dovich effect’  which is seen in early galaxies interacting gravitationally, producing hot gas and distorting the cosmic microwave background.  (The CMB is the radiation from the Big Bang.)

Most intriguing is its observations of Betelgeuse, whose diameter has shrunk since it was possible for us to resolve the disc.  (It is about a half arc second across.)  It also has a plume of gas bigger than our Solar System, and the fact that is shrinking so quickly indicates that it is going supernova in the next 100,000 years, if it hasn’t done so already.

If anyone comes across any interesting finds, let us all know, especially those where Mr Philipson says multiple rotations of the Earth were needed to get enough information because of the faintness.  Also, decent pictures of the Array seem lacking.

Clear Skies.

January’s Talk

“Magnetospheres of the planets”

Catriona Jackman is an Associate Professor at Southampton, and her main interest is in the outer planets and Mercury.

She has worked on Cassini since the beginning of her doctoral studies, and reminded us first of our early misconceptions about the outer reaches of the Solar System.

She started off with a kind of ‘did you know’ session, so I’ll continue in the same frame of mind, and hope someone reads this.

Did you know?

  • Jupiter’s magnetic field was first identified by Bernard Burke and Kenneth Franklin in 1955.
  • Have you heard of Gary Flandro? Well?  In the 1960s he realised that there would be a planetary alignment not to be repeated for 177 years.  He was the one who got JPL to start putting together plans for the two Voyager missions.  In 1966.
  • Of course you’d have to run the gauntlet of the Asteroid Belt first. Well that was fake news in the end.
  • Jupiter comes in very useful for gravity assists, because of its great mass. The lengthy Ulysses mission did a flyby of Jupiter in 1992 in order to get enough momentum to do an orbit over the Sun’s poles.  Ulysses was able to show how the Sun’s magnetic field interacts with the Solar System, and that was far more complex than expected.
  • The three Galilean satellites Io, Europa and Ganymede have an orbital resonance: four orbits of Io equal two of Europa equal one orbit of Ganymede. This is one reason Io gets gravitationally churned up so much.  Jupiter’s magnetic field also affects Ganymede; Ganymede also has a magnetic field.
  • The Cassini-Huyghens mission as revealed that Enceladus is a possible harbour for life. (-even more so than Europa, according to Prof Jackman, because it has molecular hydrogen, and this could support life.)
  • The Juno mission has provided us with some wonderful views, as has New Horizons, but it is still not known whether Saturn has a solid core.

Before you run off and google all this interesting stuff I just would like you to remember a familiar face of RAL, who I was surprised to find that she had only given two talks to us since 2103, but seemed far more public than that.  She was very approachable and loved her science.  She showed us round RAL when I went there for a tour some years ago.  There is a wonderful write up on her in the latest SPA magazine.  She was a stalwart of the SPA, having held posts as President and Treasurer.  Let’s remember her fondly, Dr Helen Walker (1953-2017).

Clear skies

Some daylight astronomy

If you fancy some daylight astronomy then the Moon will be occulting the bright star Aldebaran at 16:37GMT 23rd February 2018. The bright star should be visible in small telescopes just before it disappears behind the dark limb of the Moon. It reappears at 17:44GMT.

The picture shows Aldebaran just before ingress at 16:35GMT:

 

And then just after it’s reappearance at 17:45GMT:

Clear skies.

The Great Red Stop and a shadow transit

On the Morning of the 13th February 2018, 6am GMT, Jupiter’s Great Red Spot will begin its transit across the Earth facing disk of the planet. At the same time you will be able to see the jet black shadow the moon Europa on the disk as shown  in the picture below:

On the 24th February, also at 6am GMT, Ganymede’s shadow will cross the top of Jupiter’s disk.

Clear skies.