Meetings |
This page lists our monthly meetings. For other events open to the general public, see our Events page
Dates are set well in advance but the 'content' of the meeting is only updated (from our 'meetings database') when details are entered, so 'blank' or 'TBA' may be shown when data has not yet been entered (please be assured that the meeting will take place and a talk on (some) Subject will be delivered by (some) Speaker ! )
Meetings are held at the Church Hall (aka 'The Soltau Center') of St James-the-Less, Stubbings, Maidenhead SL6 6QW, from 7.30 (for a map and directions, see the About MAS (Where we meet) page
The Main Topic is usually delivered by an invited guest speaker. We aim to provide a diverse range of subjects linked (in some way) to Astronomy - whilst the 'Second Session' is typically delivered by one of our members. If time allows, the evening concludes with a short 'What to see this month'.
Details of a typical evening (times are approximate) :- 7.30pm. The evening starts with the Chairman delivering any important Announcements and then introducing the main speaker. 7.45pm (latest). Main Topic Speaker gets up and the lights are turned off. If you arrive after 7.45, please enter the Hall by the first door (on the right, after the entrance) and please be extra careful when finding a seat at the back of the Hall as members often setup telescopes there ! 8.45-9pm +. Coffee break during which visitors often chat with members who have set-up their telescopes at the back of the hall. If the weather is good, sometimes members will nip out for a quick look at the sky. Smoking is permitted outside the Hall, however smokers are asked to avoid any 'observers' (smoke particles always seem to get into optical equipment, no matter how well 'sealed' it may be) 9.15pm (at the latest). The 'Second Session' then runs for about 45 mins, typically ending with "What's Up !" (what to look out for in the sky this month) 10pm. We aim to clear the hall by 10pm. Post meeting Observing. If the weather is good, the Observing Organiser then leads the way to our chosen observing site, or (if the weather looks even a slight bit 'iffy) members sneak off to the local Pub instead :-)
Next meeting :
(-) 1 Mar 2019 The Extremely Large Telescope (ELT) - (Dr)
Friday, 1st March 2019 - “The Extremely Large Telescope (ELT) and large telescope design” Dr. Aprajita Verma
- Senior Researcher in Astrophysics & Cosmology at University of Oxford.
All our indoor Meetings are open to the public, however non-members are asked to make a contribution of £2 toward the hall hire costs (this may be collected by Fred, our Membership Secretary, at the door on arrival, or left at the 'Tea hatch' at half time).
This note last modified: 24th Sep 2018 13:31.
(+) 5 Apr 2019 Space Weather - (Dr Colin Forsyth)
(+) 3 May 2019 To be announced
(+) 7 Jun 2019 MAS 61st AGM
(+) Jul 2019 Summer break - (no meeting)
(+) Aug 2019 Summer break - (no meeting)
Meetings Archive |
The meetings archive gives an 'overview' of the Society activities over the past 10 years (see also the Events page).
Members have access to the full 'History of MAS' (including AGM minutes going back to 1957) along with full names and photos
The MAS 'year' runs from September of one year to June of the following. The end of year AGM in June elects the Committee for the following year (there are no meetings in July and August - although often members will meet informally at the local pub - which gives the new Committee time to 'get a grip' on running the Society)
The "short cuts" (in the 'title bar', at the very top of this page) will take you to the June AGM entry for the end of that MAS year
The Maidenhead Astronomical Society meetings archive (last 10 years only)
Missed a meeting, or can't remember when a topic was last covered ? Here is the archive of past MAS meetings.
Note that this list covers only our monthly meetings and AGM's. Reports on Observing and Other Events are separate pages
If notes were taken at the meeting, the date below is underlined and shown with a '(+)' = click to see the notes (if no '(+)' is shown, no notes were taken - or, more likely, the webmaster hasn't found them and posted them up yet :-) )
(-) 1 Feb 2019 Ask the Expert - (members panel)
Friday, 1st February 2019 - Members’ evening – “Ask an Expert”
It was noticeable that the number of members attending was less than half the normal count. This was, no doubt, due to the weather, a sort of slushy snow
Announcements
1) Matt is our new volunteer Chairman. He will be assisted by Andy.
Under the Constitution, the (only) volunteer can be co-opted to the position by the Committee. A formal vote by the Members is not required until the AGM
2) Members are asked to take part in the BAA Start Count 2019 (Deep Sky darkness survey). Running this month (February ) from Saturday 2nd to Saturday 23rd, all you need to do is count the number of stars you can see within Orion.
Ask the Experts
Tim 'chaired' the evening as Andy was unable to attend. The panel consisted of Dave H, Jim H. and Dave M. Fortunately, a number of Questions had been submitted in advance giving the team a chance to do some research !
Q1. How do you make an Occulting Bar ?
(asked by Peter H., answered by Tim H.)
As it's name suggests, and Occulting Bar is for blocking things out - specifically, for blocking out bright objects - such a star or planet, for example Sirius or Mars - so you can see much dimmer objects close by - such as The Pup or the Martian moons.
The goal is to block unwanted light before it enters the eyepiece. Whatever is being used - a piece of black tape or foil - it must have a sharp edge and has to be placed at the focal plane of the eyepiece. For a Plossl (and most other) eyepiece this is at the 'field stop', just in front of the first element of the lens assembly.
To observe the Martian moons, you will need to be using a sub-10mm eyepiece with a x2.5 or x5 Barlow. To access the field stop, unscrew the silver barrel end of the eyepiece.
A good explanation, along with photos, can be found here
NOTE that, if the tape etc. is at the correct position, it should appear as a sharp edge - if you see a fuzzy or out-of-focus edge means you are out of position.
What if you want to image the view ?
The problem is that the typical camera connects directly to the focusing draw-tube and the focal plane is thus at the camera sensor.
One solution is to use 'eye piece projection', which means you can place the Occulting Bar inside the lens as mentioned above. For more on eye piece projection, see here
Tim mentioned using the Lens Formula, 1/F = 1/V + 1/U to calculate the Focus position. Another approach would be to enable Live View on your camera and then adjusting the Bar position until the best focus position is found.
One final point from the audience was that an eyepiece with built-in cross hairs might be disassembled and the cross hairs replaced - or added to - with an Occulting Bar.
Ed. Tip for the home-builder = the focal plane is where the 'hairs' in a cross-hair eyepiece go
Q2. Does Jupiter have solid core ?
(asked by William W, answered by Jim H.)
Yes, although it rather depends on your definition of solid. Prior to the Juno mission a solid core Jupiter was predicted by one theory of how it formed. Juno suggests that below the top layers Jupiter's gravity has compressed hydrogen until it has reached a liquid form in which the electrons have been freed from the nucleus. This highly conductive mass extends from about 20% to 95% of the planet.
In the center, under a pressure of 45 million Bar or more, a rocky core is believed to exist at a temperature between 16,000 and over 30,000 °C. This contrasts with the Earth's core, which is iron at a pressure of about 3.5 million bars and a temperature of 6,300 °C.
Q3. When was the Keiper Belt discovered ? (answered by David M.)
After the discovery of Pluto in 1930, it was postulated by more than one that other such trans-Neptunian Objects (TNO's) must exist. In 1951, Gerard Kuiper published a paper speculating that a disc of objects similar to the asteroid belt formed early in the Solar System's evolution, but he did not think that such a belt still existed today.
If Pluto had indeed been the size of the Earth, as was commonalty believed at the time, it would indeed have scattered any such bodies out toward the Oort cloud or out of the Solar System altogether. Lucky for Kuiper, this was not the case.
Conformation of the existence of other TNO's came in 1992, when Albion was discovered, the first Kuiper belt object (KBO) since Pluto. As of January 2018, over 2,400 further objects have been found beyond Neptune's orbit.
Most of the objects in the Kuiper Belt are best described as 'dirty snowballs', a mix of rock and water / methane ice. This is not surprising, since the Kuiper Belt is the source of the short period (less than 200 years) comets.
The Kuiper Belt is a torus shaped area 30 to 50 AU from the Sun. Long period comets originate from the Oort cloud, thought to be spherical area from 1,000 to 10,000 AU.
On January 1, 2019, the New Horizons flew past 2014 MU69 "Ultima Thule", the subject of an Earth based occultation study mentioned in a previous MAS meeting.
Q4. In Deep Sky Stacker, with 3 dark frames 2 flat frames and 5 (jpeg) images, why is the result 'whited out' ?(posed by Matt, answered by David M)
Dave considered two possibility - one was the the software was treating the Flats as images, the other that the entire 16bit TIFF was being compressed into the 8bit jpeg output.
He suggested stacking without the Darks and Flats first, then adding these in.
During output, the histogram of the TIFF should be examined and only the section containing the image data used to generate the jpeg.
Input from meeting also questioned the use of Jpeg images, ideally RAW should be used. The Color temperature setting should be set to Manual, Daylight or Tungsten and not Auto.
Ed. In Deep Sky Stacker, a "light frame" is your actual picture image. A Flat Frame is your 50% white flat response compensation and a Dark Frame is the thermal noise compensation.
As a rule, you need one Dark for each normal image. If you don't have enough Darks, hopefully DSS will 'match up' the nearest one (in time) to each image. If you only have 3 darks, and 5 images, then it's possible DSS is not 're-using' two of the darks = this would result in an over bright result.
Flats and Bias Frames are icing on the cake.
A tutorial of DSS can be found here, however it's explanation of Darks, Flats and Bias frames is lacking (as is it's suggested approach to generating each).
Note that :-
Flats compensate for unequal light gathering through your telescopes' optical system (which is why you put the T shirt over the end of the telescope), including the cameras' sensor. So long as you don't rotate the camera in it's mounting, you can get away with a single Flat for the entire session = it's not as if your telescope is suddenly going to re-balance it's light gathering capability. NOTE that a Flat is specific to the telescope+camera setup. If you take the camera off, redo the Flat just before you start imaging again.
Darks compensate for thermal noise generated during imaging. It's very time and temperature dependent, so you really should take a Dark after each image, and this MUST be using the same time exposure. DSS will subtract the (nearest) matching Dark from each of your images. DON'T dismount your camera to 'put the lens cap on'. Take the Dark with the telescope cap on (if nothing else it will help you discover any light leakage in your system). The longer the exposure the more vital it is to have a matching Dark. It's quite possible to re-use Darks of the same exposure time - so if you are doing 10 * 30s, you can get away with one 30s Dark at the start and one 30s Dark at the end (or even just a single one some-when in the middle).
{Some cameras (eg Canon) have an automatic Dark exposure and subtraction option (you can tell since a 30 second exposure will turn into a 60 second one) - however the Canon won't allow access to the Dark, not even in RAW mode, so you can't re-use it.}
The Offset/bias compensates for un-equal response in the camera imaging pixels, more specifically for 'hot' pixels (those 'stuck on') or 'offset' pixels (those that don't start at 'zero'). The Bias can change with temperature but not by much so you can usually get away with one for the session. Of course they are so fast to do that you might as well run one off at the same time as the Dark (DON'T dismount your camera to 'put the lens cap on' - just take the Bias frame with the telescope cap on). For DSLR's, Offset Frames are really just the frosting on the icing on the cake - I doubt you will see any difference unless you are using RAW images from older DSLR's that don't have built in Bias compensation and 'hot' pixel substitution.
Q5. What are the Lagrangian points and where can I find them ? (answered by Dave H)
These positions are named after Joseph-Louis Lagrange, an 18th-century mathematician who, in 1772, discovered 5 solutions to the three-body problem at which the gravitational forces balanced out in such a way that no additional force is needed by a 3rd body to maintain it's position at that point, relative to the other 2 bodies. At other positions, a 3rd body would drift away due to the unbalanced gravitational attraction of the other two bodies.
Here is a diagram of 2 bodies, one rotating about the other eg Sun (Yellow) + Earth (Blue), or it could be Earth (Yellow) + Moon (Blue). The 5 Lagrangian points, where the 3rd, pale blue body can rest without needing to be under power to stay in position, are conventionally numbered as shown, L1 - L5L4 and L5 are stable, in that a body that drifts slightly away from that point would tend to drift back again. The other points are unstable in that a body drifting away would tend to drift further away.
The L2 point in the Earth Moon system is where the Chinese positioned Queqiao, a relay satellite launched on 21 May 2018, for their Chang'e-4 'dark side' lunar explorer. Launched on 7 December 2018, Chang'e-4 landed on Jan 3, 2019 and communicates with the Earth via Queqiao, which is in orbit around the L2 point in a vertical plane so that it can beam back Chang'e-4's images past the Moon to the Earth.
Q6. What is Escape Velocity ? (answered by Dave H)
For any body (eg Earth) Escape Velocity is the speed at which you will escape that bodies gravitational influence, assuming, of course, that you are not slowed down by other things (like, air resistance). If you start with the exact Escape Velocity you will eventually come to a (relative) stop but not be pulled back, any less than this and you will be pulled back.
This speed varies depending on how close to that body you are. If you are in orbit around the body, then your Escape Velocity is always root2 times your orbital speed.
This Velocity applies in any direction (it's not a vector). This means that if a body, such as the asteroid 'Oumuamua, is passing the Earths orbit at a speed of greater than 42.42 m/s (the Escape Velocity from the Sun at the orbit position of the Earth), then that body is an interstellar object.
When first detected, 'Oumuamua was already past the Earths orbit on it's way out of the Solar System and was going at 44 km/sec. The Sun will slow it down to it's final (and start) interstellar space speed of over 25 km/sec.
Ed. In contrast, Voyager 1s' speed is about 17 km/s and Voyager 2s', 15 km/s. In about 300 years, both Voyagers should reach the inner edge of the Oort Cloud. They will exit the Cloud some 30,000 years later.
Q7. Why does Saturn have rings ? (answered by Dave H)
Essentially, because the dust and ice particles making up the rings are within the Roche Limit. This means that the tidal forces due to Saturn's' gravity are stronger than the self-gravitational forces that could bring the particles together.
In fact, all the gas giants have (much fainter) rings = see here for more.
Ed. a good example is Shoemaker-Levy 9, which disintegrated into a 20+ fragments after passing within the Roche Limit of Jupiter.
Many Comets also pass well within the Roche Limit of the Sun and some totally break up. The more visible Comets tail is out-gassing caused by the Suns heating
The Shepherd Moons survive because the Roche Limit not only depends on the density of the moon but it's also composition (how it is held together).
Ed. The Roche limit for the Earth is about 20,000 km above the surface. Many satellites are within this limit but don’t break up because they are held together by something stronger than their own gravity :-)
Q8. Why do meteors burn up ? (answered by Dave H)
Atmospheric friction plays a part, however even more significant is the compression of the air in front of the meteor. As it's compressed, air heats up - so much so, that it will ignite the fuel in a diesel engine !
For a YouTube clip demonstration, see the "Fire Syringe".
Q9. Can you have fun with sugar ? (answered by Dave H)
Yes, see here. Get some sugar cubes and a pair of pliers in a dark room. Wait for your eyes to adjust, then crush the cubes with the pliers. You will see the some blue light flashes that are known as Triboluminescence. Many crystals exhibit Triboluminescence and generate other colours.
Explanations of Triboluminescence in sugar suggest it is an ionisation effect, however an interesting observation is that the light appears very similar to the characteristic blue/violet Cherenkov radiation given off by particles exceeding the speed of light in a medium. Whilst you can't exceed the speed of light in a vacuum, the speed in a non-vacuum is often significantly less than c. For example, the speed of light in water is only 0.75c. Cherenkov radiation is analogous to the shock wave caused by exceeding the speed of sound in air, although this seems an unlikely explanation for Triboluminescence in sugar !
All our indoor Meetings are open to the public, however non-members are asked to make a contribution of £2 toward the hall hire costs (this may be collected by Fred, our Membership Secretary, at the door on arrival, or left at the 'Tea hatch' at half time).
This note last modified: 7th Feb 2019 10:31.