What is the relationship between geographical coordinates and the use of astronomical telescopes?

The telescope in equatorial coordinate system has the greatest influence.

Because its motion is the same as the trajectory of the stars in the sky.

In this way, you need to know your geographical coordinate system, so that the international ferry of the telescope can be consistent with the trajectory of the stars.

This is easy to observe, especially those celestial photography.

Professional introduction of equatorial instruments;

You don't have to have an equatorial telescope to do astronomical observation, but celestial photography is almost an inevitable tool, with few exceptions, which is beyond the scope of this book. The equatorial camera used in Hoshino photography can be very expensive and huge, or very small and very cheap, depending on your shooting content and needs. The equatorial plane of constellation photography with wide-angle lens can even be made with only two pieces of wood and other simple parts (note). But the knowledge of self-made equatorial plane is beyond my ability. This section only briefly discusses the equatorial plane on the market (that is, $ $). In addition, since the forked equatorial plane on the market is often inseparable from the lens barrel, there is no choice. All the following discussions are only aimed at the German equatorial plane.

The first thing to choose the equatorial plane is the weight declared by the manufacturer. If the equatorial plane is not enough to carry our instruments, then of course everything is in vain. The smallest equatorial plane on the market, with a load of 5 to 6 kilograms. These equatorial planes can be observed by the eyes of a single small lens tube and can also be used for constellation photography of a single camera. There is even a subminiature equatorial plane designed to carry a single camera. Among these portable equatorial instruments, there are many inexpensive ones, which are very suitable for beginners. The load capacity of medium-sized equatorial telescope is generally 8 to 16 kg, and that of large-sized equatorial telescope is above 20 kg. The greater the load, the more diverse the observation or photography, but the more difficult it is to move.

Star photography is very different from naked eye observation. When buying an equatorial telescope, you should not only choose one with a load greater than the telescope's weight, but also reserve some space for placing additional instruments. For example, if your telescope weighs 6 kilograms and only does eye observation, you can buy a light equatorial telescope with a load of 6 or 8 kilograms. But when taking pictures, there will be not only binoculars, but also tripod head plate, star guide mirror, camera, lens barrel ring and other accessories on the equatorial plane, and its total weight is likely to reach 10 kg. In order to carry this 10 kg, a magnetic declination meter with a carrying capacity of at least 12 kg is needed.

The equatorial telescope for celestial photography has two key accessories: the motor and the polar telescope. Some cheap equatorial telescopes from developing countries look magnificent and advanced, but they are only equipped with mediocre polar telescopes and motors. If your goal is astrophotography, then no matter how inadequate your budget is, you should not consider such products.

In order to achieve accurate tracking, the equatorial plane of photography must be driven by a powerful and accurate motor. Most of the medium and large equatorial motors are built-in, so we don't have to worry. The only thing we have to do is to inquire about the evaluation of the products of this factory. Small equatorial motors are often accessories. Some small equatorial meters on the market allow you to choose a single-axis motor (that is, only the right ascension axis has a motor) or a double-axis motor (both right ascension and declination). If you only plan to shoot the star field with a focal length less than 200mm, in order to save budget, it is also possible to choose a single-axis motor. However, if your shooting focal length is above 400mm, you need to correct the motor of the declination axis when tracking with high precision. At this time, a biaxial motor should be selected. With motors, we can also see whether the controllers matched with these motors have complete motor control functions, such as forward and backward rotation, stepless or multi-segment fine-tuning speed and so on.

Polar hope is used to adjust the polar axis of the equatorial plane (that is, the right ascension axis) to be parallel to the earth's rotation axis. Its functions include observing Polaris and calculating the relative position between Polaris and the north pole of the celestial sphere according to the date and time of observation. Some dreams pass through the Big Dipper and Cassiopeia instead of Polaris. I think this should be more than ten years ago, and the accuracy is worrying. Most equatorial telescopes in Japan are fixed and built-in, which is superior to external telescopes in accuracy and maintenance difficulty (more common in American equatorial telescopes). In addition, a good telescope should be supplemented by a good equatorial level and easy-to-operate tripod height adjustment, which may be included in the evaluation project when purchasing equatorial instruments.

A good polar telescope can locate the polar axis within 2 minutes, which is enough for guiding star photography with the focal length less than 1000mm (see the section "Guiding Star-Error Source" for details). However, in order to achieve the highest tracking accuracy, it is not enough to rely only on the general polar axis gaze, and the so-called "drift method" is also needed to accurately correct the polar axis. Even so, Jiwang played an important role in the pre-proofreading of polar axis.

After the equatorial telescope meets the above basic requirements, we can look at a performance index related to the tracking accuracy of the photographic rod.

Note: When I was in high school, I met an unknown colleague (a friend of Jiazhong, if I remember correctly) on the mountain. I used this simple and self-made equatorial camera to track manually and take wide-angle photography without motor drive. I believe that only by loving and persisting in the starry sky can he take pictures in this difficult way on the cold mountain. Although I haven't seen the photos he took, it must have deeply impressed his thoughts on him and the starry sky.