Notes and Links from the June 2019 Meeting

Welcome

Moira Greenhalgh welcomed members and announced notices. The Institue of Physics has changed their programme at Lancaster University next Wednesday 12th May to ‘Pluto’s “desert”: methane ice dunes on a glacier on an airless world’. See our Welcome page.

Sky Notes for June 2019

Moira gave this month’s Sky Notes recommending for the summer nights of continuous twilight in Kendal her personal favourites high declination constellations and Globular Clusters.

Three bright summer stars are Vega, Arcturus and Deneb. The red star Arcturus in Boötes can be identified by following the handle of the Plough (Ursa Major) backwards. Globular clusters such as the compact and bright Hercules Globular Cluster can be found in the constellations of Boötes and in the neighbouring Hercules.

See also our Website Sky Notes

News Roundup for June 2019

Richard Rae presented a round-up of recent Astronomical news.

Comet Wirtanen

Results from observing the tail of Comet Wirtanen, &designated 46P, have detected a Deuterium to Hydrogen ration similar to that in Earth’s oceans. The previous cometary observations have been dissimilar throwing doubt on the proposal that cometary collisions in the early solar system could be the origin of the oceans. The 46P observations have been of the tail as the comet approaches radically close to perihelion, (close solar encounter) when the core of the comet is being blown out into the tail. Hence, the new measurements may well be more representative of the Deuterium to Hydrogen ration out of cometary cores and add weight to the theory that cometary hydrogen is the source of Earth’s oceans.

The Spacex Starlink train

Recent online videos are available showing a trail of 60 satellites through the night sky. The satellites enable greater coverage of the internet over the surface of the earth and Spacex. 20 have been granted permission for a total of 12,000.

What is a Telescope?

Simon White gave a very practical demonstration of not so much ‘What is a Telescope’ more ‘Where is that image inside a telescope’? Pairs of magnifying glasses were handed around. Members could use one glass to create an image and the other to find where it was focused and magnify it with a second glass. The conclusion became obvious, after some experimentation that the image exists behind the object all the time and the optical system of a telescope provides access to and magnifies the focussed image.

Telescope Night

Three of the members’ telescopes and the society’s 11″ Cassegrain telescope were assembled outside in the Museum yard. Members and guests could wander, mingle and question the practicalities of various astronomical telescope designs and the members’ different procedures for observing.

Notes and Links from the May 2019 Meeting

Welcome and member’s photographs

Ian Bradley opened the meeting welcoming members both new and old. He later presented some astrophotographs taken from his recent trip to New Zealand. These included the Moon and Orion completely upside down from the perspective we are used to seeing these objects in the northern hemisphere. Particularly impressive were his views of the Galaxy taken from a dark sky location in New Zealand and images of the large and small Magellanic clouds. These are the two satellite galaxies that orbit our own Milky Way and are not visible from Cumbrian skies.

April’s Moonwatch

April`s Moon watch was particularly successful with many members of the public attending. As sunset is much later during the summer months the next Moonwatch will now be in October 2019.

Sky Notes for May 2019

23rd May – Early Morning – Saturn will lie to the right of the waning gibbous Moon an excellent photo opportunity.

The Ursa Major constellation (The Plough) remains almost directly overhead above where you may be able to observe the galaxies M81 and M82.

On the 28th May, Ceres is at its closest approach to Earth. It will have a magnitude of 7( too faint for the naked eye) so with the help of binoculars you should be able to spot it. A planetarium program such as Stellarium will show you its position in the days before and after its closest approach.

News Roundup for May 2019

The News section contained updates on the two current asteroid sample-return missions: Hyabusa 2 investigating Ryugu and OSIRIS-Rex looking at Bennu. Both are near-Earth carboniferous asteroids. Hyabusa recently fired a copper bullet into the surface of Ryugu, and the mission will seek to capture some of that pristine debris and, like OSIRIS-Rex, then return to Earth.

The other big news was the picture of the black hole – M87* – at the centre of a supergiant elliptical galaxy in Virgo, about 55 million light years away. The image was obtained by Very Long Baseline Interferometry, using eight radio telescopes collecting radiation with a wavelength of 1.3mm. UCLAN are part-sponsors of the James Clark Maxwell telescope in Hawaii which provided one point in one on the baselines and were also involved in analysing the data.

A high-res image of the black hole in M87

Dr Sarah Badman, Lancaster University on “Auroral Activity in the Solar System”


In this Cassini image below a band of southern aurora in visible in green.

An excellent talk, which was most informative was delivered by the very competent researcher, Dr Sarah Badman. She explained early in her career she was able to work on data received from the Cassini spacecraft just after it had arrived in orbit around Saturn.

The mechanism for the aurora borealis was explained whereby charged particles emitted from the sun interact with the Earth’s magnetic field, are given energy and collide with atoms and molecules in our atmosphere. These collisions result in ionization of the atmosphere which makes up the aurora. Collisions with oxygen produce red and green auroras, while nitrogen produces blue and purple colours.

Aurora in other solar system planets occur only if a magnetic field is present to interact with the solar wind. The images presented in the talk were quite stunning.


Hubble composite image of aurora on Jupiter

Here the image shows a curtain of glowing gas which is wrapped around Jupiter’s north pole.

Notes and Links from the April 2019 Meeting

Members’ Observing Sessions

Now that the clocks have moved forward one hour the next Members’ Observing Session will be in late September. We still need volunteers to organise a few future Members’ Observing Sessions.

Sky Notes for April 2019

  • at dusk on the 5th April Mars lies on a straight line between the Hyades and Pleiades
  • the Orion constellation is now setting shortly after the sun but Leo (the backwards question mark) is well placed high in the south from dusk containing a number of galaxies
  • Virgo, rising at 9 PM, contains Markarian’s Chain and the galaxies of the Leo Triplet including M65 and M66.
  • the Ursa Major constellation  (The Plough) is almost directly overhead above Leo again including many galaxies. M81 and M82 are very close together above the ‘saucepan’, and M51 the Whirlpool Galaxy [and actually in Canes Venatici] is just below the end of the ‘tail’. 

Markarian’s Chain taken by to our member Simon White

News Roundup for April 2019

Hayabusa2 takes fires at Ryugu

At the end of February Hayabusa 2 took a sample from the sub-surface of the asteroid Ryugu after an orbiting module fired a bullet at the surface. The meeting was shown a comparison between Ryugu and Bennu, the target of the OSIRIS-REx mission . While similar in shape, Ryugu appears smoother and more rounded than a typical asteroid and proves to be hollow and totally lacking water. By contrast, Bennu contains water and volatile molecules possibly from the early solar system.
 




Ryugu




Bennu

 

While cosmological distance determines age the opposite does not have to be true. Some of our faint satellite galaxies prove to have been among the first formed in the Universe.

Furthermore, a star does not need to be far along the in its life before the first planets a formed. From the lack of any elements heavier the Helium, the young HR8799 already has four giant, exoplanets.

The Drake Equation

A member gave a talk on the history of the Drake Equation proposed in 1961 to estimate the probability of another civilization in our Milky Way. Since its proposal, we now have much more quantifiable numbers for factors such as the fraction of those stars that have planets some factors. Nonetheless, many factors, such as the fraction of planets that could support life that actually develop life at some point are still highly conjectural.

Stuart Atkinson  Unseen Apollo – Images from the Archives

EAS member Stuart Atkinson gave an illustrated talk with images from the Apollo programme rarely publicised. Only five images exist of Neil Armstong on the first moonwalk. Other than the reflection of Armstrong in Aldrin’s visor the other four only show parts of his body.

Among a number of lesser-known facts, the size of the Saturn V rocket to launch the modules and their engines to the Moon as compared to the more recent Shuttle.

See also: NASA Apollo missions

Notes and Links from the March 2019 Meeting

Member’s Observing Sessions

An appeal was made for volunteers to organise future Member’s Observing Sessions after this month.

Amateur Radio Astronomy

One of our members gave the first of a series of short talks on opportunities for amateurs using radio equipment.

After a brief history of Radio Astronomy, the possible motives were listed. The natural phenomena of meteors, Jupiter, the Sun and associated Aurora can be monitored together with satellite communications. Although radio astronomy can be carried out during the day at frequencies above 30MHz, frequencies below this are either absorbed or reflected back to earth or back into space by the Earth’s ionosphere. When sunspot activity is low after sunset there is an opportunity to listen to frequencies below 30MHz from space when the F layer of the ionosphere can fade a few hours after sunset. It is then possible to hear radio emissions from Jupiter between 15 and 38MHz.

An example of how to listen to meteors was given, and later some theory to explain why radio waves at different wavelengths are able to penetrate different media . An explanation on different antennas was given with an example of a simple YAGI antenna showing how this and Dishes are able to increase the Gain of a signal and improve the signal to noise ratio. The presentation finished with brief examples of equipment which will be discussed at later presentations.

Sky Notes for March 2019

  • Orion only a few more weeks. Betelgeuse at Right Ascension of 6 hrs sets six hours at the Equinox on the (1830 on the 21st).

  • from March 26th to 31st – early evening: Mars approaches the Pleiades and Hyades open clusters

  • on Friday, March 29th – before dawn around 05:45: Saturn just above the Moon above Uranus

  • See also Ian Morison’s Night Sky this Month on the Jodrell Bank site in Sky Notes and our EAS links page

News Roundup for March 2019

Our EAS member, Richard Rae, visited Complex 39A at Cape Canaveral ( the Appollo 11 launch pad) for the launch of the SpaceX Falcon 9 rocket which is now the workhorse for vehicles to and from the International Space Station.

Simon White of EAS “Anatomy of an Astrophotograph”

   

Simon White gave an explanatory talk with illustrations of the process of doing astrophotography – from loading the kit into the boot of the car…..

       
 

….. to the final photographic image of The Orion Nebula.

 

Simon’s talk covered various important steps in capturing the data, including… 

 

Setting up the telescope in a dark lay-by

Polar alignment of the mount

Tracking the sky and guiding on a single star

Focusing with a Bahtinov mask

Taking the photos

Calibrating the frames

 

Stacking the frames before the post-processing

Getting help online to adjust the colours

Final adjustments to bring out all the detail captured in the data

See also: Simon White’s Orion’s easy target and our Links page:  Software used by our members    

Notes and Links from the February 2019 Meeting

Member’s Observing Sessions

The Chairman for the meeting appealed for volunteers to organise future Member’s Observing Sessions after this month. For this month we will include a waxing, crescent moon hopefully before our Public Moon Watch on Saturday 16th February.

News Roundup for February

Sky Notes for February

Member’s Photographs

An EAS Member displayed his impressive time-lapse video and Astro photographs recently of:
  • 40 second time-lapse of last month’s Total Lunar Eclipse
  • Image of the Crab Nebula
  • Image of the Orion Nebula

Dr Steve Williams of Lancaster University speaking on Nova Explosions

A Nova explosion owes its name to what was once considered a ‘New Star’. Nothing could be further from the truth.

Observed novae involve closely located binary stars one of which is a White Dwarf. A white dwarf is the remnant dense core of a star at the end of its life. No nuclear processes are occurring and the star is steadily cooling. The white dwarf draws hydrogen from the nearby companion main sequence giant star which covers its surface. If the hydrogen gets hot and dense enough, nuclear fusion occurs on this surface and the white dwarf star brightens, a ‘Nova’ explosion, until most of the hydrogen is used up and the star dims and the process starts again… If the White Dwarf gains mass to exceed 1.4 solar masses, a supernova is possible – although the exact mechanism for this is still unclear and is thought to only occur with carbon-oxygen white dwarfs and not carbon-neon white dwarfs. Research is still ongoing into this fascinating subject.

 

Visible light is suddenly emitted in a characteristic, exponentially decreasing light curve. The known curve allows time of initiation and then the absolute magnitude of the Nova to be determined and thus the distance from any apparent magnitude that was caught on an observation.

Not only visible light is suddenly emitted but also x-rays that do not penetrate the ejected shell of unburnt hydrogen until the shell density drops to a known level that allows the size of the shell to be determined.

Unlike Supernovae, Novae both leave behind a remnant that may last for centuries and the ejected shells fall back onto the remnant. The whole process may subsequently repeat many times in known Recurrent Novae. A number of Recurrent Novae have been discovered by inspection of archived observations. With the current telescopic ranges, all observed novae occur either in our own Milky Way or our companion and satellite galaxies – such as The Andromeda Galaxy and the Magellanic Clouds. Detection is difficult in the Milky Way because of obscuring dust along the plane of the galactic disc. Around 40 new Novae/year are discovered in the Milky Way – a number still being discovered by Amateur Astronomers.

See also links from Nova on Wikipedia

Notes and Links from the January 2019 Meeting

AGM

Chairman’s report on the work of the committee over 2018.

Chairman stood down and a new committee was elected making seven members in all. Chairman for 2019 to be selected at the next Committee meeting.

Sky Notes for January

Total Lunar Eclipse enters the full eclipse stage 04:45 Monday morning 21st January See: https://www.timeanddate.com/eclipse/lunar/2019-january-21

and: Upcoming Eclipses

News Roundup

Ultima Thule

After the flyby of Pluto last year, a few days ago the New Horizon mission encountered the most distant object ever visited and returned images of Ultima Thule from the Kuiper belt. Thule is about 31 x 19 km and looks to be two objects that coalesced into a snowman shape.

See also: NASA’s Mission to Pluto and the Kuiper Belt.

Chang’e 4 landing on the far side of the Moon

On the 3rd, China’s 1.2 ton Chang’e 4 probe made the first landing on the far side of the moon. After touch down a 140kg rover was deployed. A satellite is being kept in a high orbit, around a theoretical Lagrangian point, relaying all the comms between Earth and the remotely controlled lunar vehicles Chang’4 Relay Satellite.

Part of the exploration programme will be to return samples to Earth by Chang’e 5 and Chang’e 6 Chinese Lunar Exploration Program.

See also: https://en.wikipedia.org/wiki/Chang%27e_4

Society Telescopes

The society has a number of telescopes available to members for as long as the member wishes to retain and keep them in good condition. One exception is the recent donation of an 11″ (28cm) Schmidt-Cassegrain. EAS is sharing the telescope with Cockermouth Astronomical Society where it will be available to EAS from late December to late June each year.

Dr James Osborn talk on Adaptive Optics

Dr Osborn gave a talk on his work on providing instrumentation for the world’s large, optical telescopes.

The marked rapid introduction of atmospheric distortion from a small to a large telescope was illustrated where the star images in the latter visibly oscillate. Astronomers and engineers are developing adaptive optics technology to remove such atmospheric bouncing and blurring so that scientists can see distant objects more clearly.

The disturbance to wavefronts from the target area is measured by using a laser to excite sodium atoms in the atmosphere to create an artificial star-like object. Fibre optic communication systems relay measurements of the distorted return signal to computer systems that control the telescope correction equipment. The AO system corrects the atmosphere distortion of the wavefronts from this artificial star in real time by flexing mirrors at a kilohertz rate to compensate for the atmospheric turbulence in the direction of viewing. Conformation and calibration of the laser systems are achieved at sites by a number of proved systems around the large telescope.

Q&A was informative. Included in that was the fact that in many parts of the world where large telescopes are located there is no need to warn aviation when launching 20 watts of laser light into the sky.

See alsohttps://en.wikipedia.org/wiki/Adaptive_optics

Notes and Links from the November Meeting

Chairman’s announcements

The chairman welcomed members and guests to the November meeting.

A Celestron telescope of some vintage has been donated to the society. Currently, the telescope is being renovated, mould removed from the tube and optics, to be used at EAS Observing Sessions.

Sky Notes for November

Astronomical Dark now begins before 7pm.

Mars is the only feasible planet for observing this month and there are two periodic comets, one the target of last year’s Rosetta mission, that will be visible towards the end of November. See  Sky Notes.

Observing Evening

Check for the  Observing Evening,  page for the next member’s evening.

Dark Sky accreditation for the Lake District

Johanna Korndorfer presented a talk on the work of Friends of the Lake District to gain internationally recognised ‘Dark Skies Reserve’ status for the Lake District National Park.

Concepts of Dark Sky Accreditation were introduced together with the implications for and actions to be potentially taken by authorities. In particular, ‘Core’ dark areas in the Lake District and surrounding ‘Buffer’ zones, where light pollution will impact the Core, need to be identified. Members were asked if they wished to help measure the sky darkness using light meters loaned to them by Friends of the Lake District.

An extensive Q&A followed querying the implications for towns and rural communities.

An illustrated talk on Hyabusa2

After a speaker cancellation, David Glass valiantly presented a talk on the progress of the probe Hayabusa 2, now in orbit around Type C (low metal mostly rock) asteroid Ryugu.

Of particular interest:

Of the multiple propulsion systems, the  Ion drive thrusters, with a force of micro-Newtons that consume a small amount of fuel over long periods, are deployed to adjust the inter-planetary transition orbit. The Ion Thrusters consume far less fuel than conventional thrusters.

Hayabusa 2 will launch a number of deployable modules designed to land on Ryugu and bounce up to 15 times between measurements and experiments.

A Small Carry-On Impactor weighing 2 kg will be ‘fired’ at a selected area of Ryugu to create a crater, while the main module hides behind the asteroid, where the sub-soil will be revealed as a target site for material sampling.

Hayabusa 2 will retrieve samples from the target crater and two other sites and then return a capsule of samples back to Earth.

Member’s Astrophotographs

Finally, a member presented some recent astrophotographs taken in the Kendal area.

Notes and Links from the October Meeting

 

Chairman’s announcements

The chairman welcomed members and guests to the October meeting and commented on the result of a recent feedback survey on how the club was meeting its expectations; news items and sky-notes were well received by respondents and lectures were reckoned to be set at a level “about right” for most of the audience.

Sky Notes for October

Mid October the skies are astronomically dark at 8:15. A general roundup was made of the many objects to be seen in the October sky. Lots going on!

Observing Evening

If the observing evening was not organised this weekend then it may be prudent to wait until around the 31st October when the skies were dark at 6:45 pm. Members were again reminded to check the web page,  Observing Evening, on this site and not to travel to an observing evening unless the red text had changed to blue!

Astronomical News

Tess

This exoplanet detecting satellite is now fully operational and monitors the change in luminosity of nearby stars that may indicate planets. Proving to be very capable data is now being received from Tess that is characteristic of planets passing in front of stars. Further updates to follow.

Hyabusa2

David Glass explained the intricacies of this fascinating Japanese project that involves instrumentation landing on the asteroid termed Ryuga. Of interest to early solar system research, this operation will aim to capture material from the asteroid and return it to Earth for further analysis. For a detailed but (mostly) understandable description, see: Hayabusa 2

Further News

A recent photograph of Opportunity on Mars that has now lost contact with its project team.

Analysed data from ESA`s Gaia surveyor has narrowed down where the interstellar traveller Oumuamua may have come from. The database combined with trajectory science has narrowed the source of Oumuamua to 4 stars within our galaxy.

Bright objects on Ceres have now been associated with mud deposits. New research has indicated water and rock have erupted and may be responsible for the bright surface detail on the surface of Ceres.

Guest speaker: Prof. Lionel Wilson of Lancaster University who spoke on recent ideas on the volcanic history of the Moon

An interesting talk on the ancient volcanic lava flows on the moon and how there may be lessons to learn with Earth`s volcanism both in the past and in the future!

IMP`s and RMDS were discussed at length. These are Irregular Mare Patches and Ring Moat Dome structures. 70 IMPs have been discovered 19 of which are around obvious vents. The recent research indicates there may be consequences for the Earth because we may be due a major basalt eruption on a scale of an extinction event.

The far side of the moon has a crust that is 60% thicker than the nearside that faces Earth. Most volcanism occurred on the nearside face of the moon and occurred more than 1 billion years ago.

Eruptions on the moon form dome shapes because there is no atmosphere. Sinuous rilles (look like rivers) form due to the thermomechanical erosion of the surface of the moon and can extend for several kilometres; the turbidity of the lava flow and a high lava discharge rate are key features in their formation.

Ring-Moat Dome Structures (RMDS) are a newly discovered feature on the lunar surface; low domes surrounded by a shallow cavity or moat. Large-scale lava flows are now thought to have occurred on timescales much more rapid than previously thought.

Theoretical models were discussed regarding their construction and magmatic foams were highlighted as a possible precursor. Over 2000 of these structures (RMDS) have been identified.

For further details see the recent Geophysical Research Letter: –  Newly Discovered Ring-Moat Dome Structures in the Lunar Maria

Notes and Links from the September Meeting

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Chairman’s announcements

The chairman welcomed the Dark Skies Project Officer for the Friends of the Lake District and asked for volunteers to be a liaison to work for dark Sky Accreditation. A communication from Ullswater Yacht Club who are looking to open their grounds for the use of members. Members were notified of UCLAN public lectures in Lancaster and Preston during October 2018. Members asked to finalise their requests to visit Alston Observatory after the next meeting on Tuesday 2nd October.

Astronomical News

Two news roundups were given by two members. Galaxy news links: Solar Orbiters: Miscellaneous items

More Astronomical News

The Ecliptic

Arising from question Why Mars farther than other planets from Ecliptic last year. Planetary orbits are inclined to the ecliptic plane by up to 6° (maximum reached by the planet Mercury). The Ecliptic coordinate system, Celestial equator, Ecliptic and Celestial poles were covered as well as equinoxes.

Not to be confused with the orbit shape ‘ecliptic’ the word comes from the fact that when the moon crosses the ecliptic we experience an eclipse.

Sky Notes for September

From the Ecliptic the meeting was focused to the constellations near to the Zenith, where starlight travels through the minimum depth of atmosphere to the telescope. By the middle of September, we will be experiencing 7 hours of Astronomical Dark from 9 PM. See  Sky Notes in particular.

Guest speaker, Stuart Atkinson Famous Fake Astrophotos

Stuart gave an entertaining but informative talk that also warned of the dangers of false attribution of astrophotographs taken by members. Since the advent of digital cameras and post-processing software images are not only easy to fake, as opposed to the valid enhancement of target features. In addition, the internet has released a Pandora’s Box where the distribution fake images become impossible to control. Images were illustrated from obvious Artistic impressions being passed off as factual to the deliberate stealing of images. For the latter, defences were outlined such as ‘Watermark’ signing to the proven method of introducing errors.

Notes and Links from the August Meeting

Chairman’s reports

This Saturday, 11th August the Perseid meteor shower will occur on a moonless night. However, the forecast at the moment is poor.

Astronomical News

  • Members may still join arrangements for a second visit to Alston Observatory is being organised for Tuesday 2nd October
  • The NASA Parker Solar Probe is due to be launched this Saturday 11th August. The probe will fly into the solar corona and will investigate the Solar wind and the heating of the solar corona to very high temperatures.
  • A pair of images of Neptune illustrated the gain in using new Adaptive Optics by the VLT. The images demonstrate that the VLT with the latest adaptive optics can be competitive with the Hubble Space Telescope. The new technology is also applicable to the future 40m-class telescopes (e.g. the E-ELT) and is essential to get the best out of these new assets.
  • The MeerKAT interferometric radio telescope in South Africa can now produce science images. An image of the centre of the Milky Way was shown, which reveals new detail of unexplained filaments in the region.

Orbital Physics and Spacecraft Manoeuvring

A member gave an Illustrated talk and demonstration to explain an orbit: throw hard enough until your ball goes over the horizon and continues to fall towards the planet at the same rate as the ground ‘falls away’ due to the curvature of the planet resulting in a circular orbit. The problem of manoeuvring without changing orbits was illustrated with the failed docking scheduled for Gemini 4 before their first spacewalk. From a distance, increasing speed by the trailing vehicle changes the vehicle’s trajectory into a higher and more elliptical orbit.

Olber’s Paradox

  Why is the night sky dark?   A member’s talk described the paradox attributed to  Heinrich Wilhelm Olbers ( 1758–1840).  Given an infinite number of stars that compensate intensity decrease with distance, the night sky should light. Although the Big Bang specifies that the material in the universe is finite, there are more than enough galaxies to cover one per a pixel on telescopes in the foreseeable future making the paradox still valid. The currently the solution accepted is that space is expanding: thus, cooling radiation and shifting radiation towards the red and radio. Other explanations are also mooted.

Explanatory solution addendum added by a member:

Infinite or not, the universe is of a size that means that even travelling as fast as they do, photons from some distant stars have yet to reach us. There will certainly be some redshift arising from the expansion of the universe, but this effect can be ignored by recasting the paradox in terms of radiation generally, rather than the much smaller visible spectrum. So irrespective of wavelength, the paradox is why there is not an infinite bath of radiation. The “fractal” explanation is a way round the homogeneous assumption inherent in the paradox, and as in the talk, the fractal calculations of the universe diverge from the required dimension. So I think we’re left with the “it hasn’t reached us yet” solution. And, of course, it never will reach us – but that’s a different talk.

Telescope Mount Alignment

The types of astronomical telescope mounts were explained by a member:  Altazimuth  and  Equatorial . Current ‘GoTo’ software offers the opportunity to iterate polar re-alignment. How accurately does the polar alignment need to be for time exposure photography? After much work and many calculations , our member discovered that the error reported by the software, for the polar misalignment, may be used as the drift across the image in 24 hours. Hence the rate of drift can be quickly calculated. The pixel coverage for a given camera together with the focal length of the system can be used to determine the sky coverage per pixel, eg 2 arc seconds/pixel. The rate of drift can then be used to determine the time to drift across one pixel (or maybe more) to find the maximum exposure time for the reported polar alignment error. In summary, tolerance for the error in polar alignment can be calculated beforehand. The telescope polar alignment procedure can then cease when within the desired tolerance.