What would an amateur need to make accurate astronomical measurements?

[mihaivzr]

TL;DR Summary

For something like using a 70mm 2 arc-second resolution amateur telescope and being able to describe the celestial sphere position of an object of interest with 5 arc-second accuracy.

Planning to manually rediscover or confirm our exact place in the Solar System, Galaxy and Universe. I've noticed that even 50 mm high quality amateur telescopes are likely well better than what Galileo Galilei era scientists had for the first half century. The theodolite looks like an inspiring design, but for amateur purposes I would search for a best solution under 10 kg. The sextant seems unreliable for the 5 arc-second accuracy target. It would have to be a special design attached to a larger telescope that would actually look more like an equatorially mounted theodolite. The entire accurate observing solution has to be light enough for backpacking to a remote area without light pollution. Calibration in a new location should not be longer than 1 hour. Scaling up the ideea maybe considering a 100kg personal car driven telescope assembly and 4 hours of calibration.

 

[russ_watters]

You'll have to be a lot more specific about the measurements you want to make. At least that last one and probably the second isn't possible with amateur equipment.

 

[sophiecentaur]

TL;DR Summary: For something like using a 70mm 2 arc-second resolution amateur telescope and being able to describe the celestial sphere position of an object of interest with 5 arc-second accuracy.

The sextant seems unreliable for the 5 arc-second accuracy target.

I'm not clear what you actually want to do. How basic do you want your regime to be? When you say "manual" do you mean without photogtaphy". With today's light pollution levels you have no chance without the benefits of photography and image processing.

Using Tables of ephemeris would hardly be 'cheating' unless your 'rules' are very tight. There is a lot of data about the positions of most of the heavenly bodies and how they will change with time but all that's been gathered over a long time and with expensive equipment.

TL;DR Summary: For something like using a 70mm 2 arc-second resolution amateur telescope and being able to describe the celestial sphere position of an object of interest with 5 arc-second accuracy.

exact place in the Solar System, Galaxy and Universe.

I'd suggest that you try to be realistic about your project; in one lifetime, you have no chance of making a large star catalogue from your own measurements. Do you happen to live somewhere with reliable clear skies, for instance? You can use fairly basic equipment to measure the distances from Earth to the Moon, Earth to the Sun and the orbits of some planets. The Greeks managed to work out the distance to the Moon with very creditable accuracy (after, of course, measuring the radius of the Earth, and that may be achievable with humble equipment, for instance. You would have problems with the parallax method for stellar distances because that uses a long time scale and you'd be needing to make up your own star atlas to rely on some stars to be considered 'fixed' so you could then observe the movement of nearer stars by parallax over the year.

Don't underestimate how big a task this could be; you could easily fall out of love with a task that's just too much for one person to handle. Start in a small way and build up.

 

[Baluncore]

A portable equatorial mount will require GPS (or a very good map) to set up the mount. Knowing the time will require GPS.

This project will rapidly become an exercise in computing and digital astrophotography.

https://en.wikipedia.org/wiki/Schmidt_camera

 

[sophiecentaur]

This project will rapidly become an exercise in computing and digital astrophotography.

In terms of what the OP seems to expect, this has to be true. But there are a number of lower tech measurements that can give a worthwhile knowledge about the scale of things up there. We can 'cheat' with GPS to find the distance between two locations on Earth and with a pair of good watches to synchronise observation times (instead of surveyor's chains and a total eclipse), the altitude of the Sun (with two sextants) in the two locations can give you the radius of curvature of the Earth. It's a shame I just couldn't be bothered to do that exercise but getting a reasonable answer would certainly give one a rosy glow of satisfaction.

There are other clever bits of trigonometry which can be used to do closer measurements and all you need is a simple scope (and a solar filter!!!!! of course, when appropriate). Nowadays, the 'right answer' is always available as a check.

 

[Tom.G]

What would an amateur need to make accurate astronomical measurements?​

Around 8 to 12 lifetimes, then you can start to get accurate and complete data.

 

[mihaivzr]

A portable equatorial mount will require GPS (or a very good map) to set up the mount. Knowing the time will require GPS.

This project will rapidly become an exercise in computing and digital astrophotography.

https://en.wikipedia.org/wiki/Schmidt_camera

What about adapting a 12x50 monocular to a high end sextant clamped to sturdy tripod? Once patiently calibrated on a tripod I would naturally expect to be able to reach equipment precision limits on accuracy (maybe helping with a pocket comparator too; maybe patiently finding and recording fine corrections to apply to scale readings). Using 10's of measurements and some statistics maybe even get to an order of magnitude better down to 0.5'' of accuracy.

Astra IIIB sextant looks interesting. It has a 7x35 monocular telescope as a factory option. The stated accuracy for very good nautical navigation hand use is 15''. It's vernier scale precision goes down to 6''.

https://www.celestaire.com/product/astra-iiib-sextant/

It seems that for measuring the culmination altitude, using a high quality (low drift) watch and a hand held sports chronometer should get enough accuracy (the sky moves 15'' (arc-seconds) east-west in each clock second, but the height-altitude of a star varies much more slowly at culmination time).

https://en.wikipedia.org/wiki/Transit_instrument

 

[Baluncore]

What about adapting a 12x50 monocular to a high end sextant clamped to sturdy tripod?

What do you really want to do?

A surveyor's theodolite such as an old Wild T2 will get you down to an arc second. It sits vertical on a tripod. For observation at night, I would replace the eyepiece with a fixed camera, then video record the star as it crosses the field, preferably rising or falling vertically, which will eliminate variations in atmospheric refraction, giving true direction. Program the display to show digital crosshairs, so you can see them at night. I find stars disappear behind physical crosshairs, just when I need to see them the most.

I have a Wild T3 here that began life in 1950s USA, doing starsights to set up the orientation of missile silos. It reads accurately to half of an arcsec. The only thing that could beat it is a T4, but that is now well outside my budget.

Take a look at the design of the ultimate, a Wild T4 astronomical theodolite.
https://www.wild-heerbrugg.shop/index.php?cPath=1_3_5_25_63
You should be able to make something in that wide arm style, with a high-resolution camera. Maybe use a photographic reflex lens for the telescope, with focus clamped at infinity. Consider a second hand Maksutov-Teleobjektiv MC MTO-11CA, 550mm or 1100mm, or a Minolta AF Reflex 500mm F/8 Mirror Lens.

 

[sophiecentaur]

What about adapting a 12x50 monocular to a high end sextant clamped to sturdy tripod?

It's not actually clear what you want to do. If you want to determine the position of a star in the celestial sphere by just looking at it and measuring its apparent Az and El, you would need to take into account the atmosphere (things dance around all the time due to the atmosphere).

But, seriously, you need to be a lot more precise about how you intend to go about finding " our exact place in the Solar System" etc. What do you mean by "exact"? I already suggested using ancient methods of finding some of the distances between Earth and other nearby objects. Your sextant idea could come in handy there. You need to remember the 'horizon' is bumpy except over the sea or would you, perhaps, use a good plumb line to give you a vertical reference?

Have you read around about how these measurements have been made in the past and the errors / problems involved? Unless you have a serious plan for this, you could end up spending a lot of money on equipment which may not even do the job you want. We've all been there - fancying a certain piece of equipment and trying to do something 'valid' with it. This is true for anglers, DIYers, sportspersons and many others. Plan in great detail before deciding to buy anything.

A successful limited project is far more satisfying than an expensive, ambitions project that doesn't;t get off the ground.