HEQ5 and Sidereal rate

[M40]

Hello all, I am working my way through a few books as I seem to have an abundance of spare time during the day and more than a couple of clouds at night, so.....

As I understand sidereal rate, this is the time taken for a body to orbit the sun, as such Earth sidereal rate is 1 year and all the other planets have a different sidereal rate. On the synscan handset, when you set to track Mars for example, the speed of tracking is set to sidereal rate, which I presume is Earth sidereal rate, which explains why I have to keep centering Mars in the scope.

In order to overcome this, is this where guide cameras and the associated software comes in?

And I can't quite get my mind around it at the moment, but the DSO's are also tracked at sidereal rate in the synscan which again would need centering periodically?

Does that sound right?  

Enjoy

[Laurin Dave]

Sidereal rate in the handset is correct for tracking the planets, it sounds to me as if your polar alignment is off,  your mount will also have periodic error which will cause the planet to oscillate back and forward along the East West axis but only by about 3-4 Mars diameters each way and not really a problem for visual

[Skipper Billy]

My understanding is that sidereal rate is the rate at which stars move across our sky - a sidereal day i.e. one full rotation of the earth is about 23 h 56 m 04.091s

The Sun and moon track at different speeds to almost everything else which is why there is often a Sun and Moon setting on a mount.

So if Mars is drifting out of your view the problem isn't the chosen sidereal rate it sounds like something else - polar alignment would be my first guess.

With a guide camera you could guide on an object but more usually the guide camera is used to issue tiny corrections to the mount to make up for deficiencies the mounts accuracy.

DSO's track at the normal sidereal rate and should be static in the viewfinder.

HTH !

 

 

 

 

[vlaiv]

Sidereal rate has nothing to do with time taken to orbit the Sun. It has to do with Earth's rotation.

There are usually three different tracking rates - Solar, Lunar and Sidereal.

Sidereal is "pure" earth rotation rate and is used for fixed objects like stars, but also for planets - because they don't move much during single day and their proper motion simply can't be perceived as motion at the eyepiece (it takes several hours for planets to move just a tiny bit with respect to background stars).

Lunar tracking rate is combination of Earth's rotation and also Moon's orbital speed around the Earth.

Solar tracking rate is combination of Earth's rotation around it's axis but also orbital speed of Earth around the sun.

Guiding has nothing to do with above rates - it is designed to deal with couple of things - primarily imperfections in mechanical components of the mount. These are not perfectly circular and mount does not track perfectly well. Guiding is needed for long exposure astrophotography because these imperfections result in stars being smeared instead of points. It also deals with polar alignment error and refraction in the atmosphere.

It is not needed for observation, nor planetary imaging since involved "exposures" (remember that we can watch movies because we "see at about 30fps") are far too short.

Fact that DSOs move out of your eyepiece will most likely have to do with

a) wrong tracking rate selected - lunar or solar instead of sidereal

b) very poor polar alignment

[M40]

Thanks people, looks like I have got to read that chapter again 🤣 and just checking, the sidereal period of Earth is one year doh...🤦‍♂️

It doesn't surprise me that the PA is off, I virtually never see the whole of ursa minor and it can sometimes be difficult for me to see Polaris.

On tracking, if I set it to track Mars, the rate is auto set to sidereal so I know that bit is ok 🤦‍♂️ not really tried with DSO yet as I have been trying to sort myself out whilst I can still see Mars, Jupiter and Saturn. 

Thanks 👍

[Neil H]

Hi you could try polar alginment pro you can do a day time alginment i use this if i set up were i cant see polaris 

[andrew s]

While it looks like polar poor alignment you won't get good tracking close to the horizon due to refraction which modifies the apparant sidereal rate.

Regards Andrew 

[M40]

2 hours ago, Neil H said:

Hi you could try polar alginment pro you can do a day time alginment i use this if i set up were i cant see polaris 

Had a look at the polar alignment pro youtube video's and downloaded straight away £2.49p later and it looks good. Even if it's not 100% it will get me in the ball park 👍 Great shout, many thanks Neil.

2 hours ago, andrew s said:

While it looks like polar poor alignment you won't get good tracking close to the horizon due to refraction which modifies the apparant sidereal rate.

Regards Andrew 

Talk about learning all the time, many thanks for the info Andrew 👍

[LongJohn54]

On 26/11/2020 at 11:51, Skipper Billy said:

My understanding is that sidereal rate is the rate at which stars move across our sky - a sidereal day i.e. one full rotation of the earth is about 23 h 56 m 04.091s

 

Nailed it there!

A normal 24 hours is the time taken for the earth to rotate enough to point exactly at the sun.

A sidereal 24 hours is the time for the earth to rotate exactly 360 degrees.

Therefore stars appear at exactly the same sidereal time which is why RA is described as a time.