Aside from the laboratory instruments we are familiar with, astronomical instruments are another type of Scientific instrument. Understanding their various categories and formulas will help you determine its proper usage.

Scientific instruments are not confined to laboratory equipments only. An example is the Hubble telescope. Particular categories of scientific instruments include the following:

• Measuring instruments

These are devices used to measure or compare the magnitude of physical properties such as:

- voltmeters
- speedometers
- timers and
- clock
- weighing machines and others

• Analytical instruments

These are devices used to measure multiple or complex material properties like mass spectrometers.

• Astronomical instruments are used to:

- observe
- record and
- measure the position of heavenly bodies such as

* Stars
* Planets
* Comets and others

Here are examples of astronomical instruments:

An Optical Telescope

The function of a telescope is to gather light and to magnify the image. The bigger the main "light-collecting element" of the telescope, more light gets collected. It is actually the whole "amount of light" collected that determines the level of detail.

All optical telescopes are categorized into one of three classes:

1. The Refracting Telescope

With a refracting telescope, light is collected by 2-element objective lenses. It will then bring it onto a central plane.

2. The Reflecting Telescope

A reflecting telescope uses a type of concave mirror to collect light.

3. The Catadioptric or Mirror-lens Telescope

A Mirror-lens or Catadioptric telescope uses a good combination of these lenses and mirrors. It results to a shorter and more convenient optical tube assembly.

All telescopes use an eyepiece. It is located behind the central plane. This is to enlarge the image formed by the major optical system.

Other instruments can be placed in the central plane for different purposes. These purposes include the following:

- photo-electric cell to measure the luminosity
- the slit of a spectrograph to evaluate the light or
- thermo-couple to measure temperature

The advantage of a reflecting telescope is that it has no chromatic irregularity. Mirrors can be made to a much larger size.

The enlargement of a telescope is given via this formula:

M = OF / f, -------------------- (1)
where OF is the central length of the objective and f that of the eyepiece.

The resolution limit of a telescope is given via this formula:

R (in sec of arc) = 2.3 x 105 x ( /A), ------------------- (2)
where is the wavelength and A is the diameter of the aperture.
For example, if A = 100 cm and = 4000 x 10-8 (yellow light) then R = 0.092"

INTERFEROMETER

An Interferometer is used to determine the size of astronomical objects. This is through careful analysis of the following:

- resulting interference pattern,
- position of a point source or
- Fine details in an extended one can be resolved.

The same formula is done for the resolution that is appropriate except for aperture A. Aperture A is replaced by the baseline between the two receivers. This method has been widely used via radio telescopes. It is also applied with the use of optical telescopes.

RADIO TELESCOPES

Radio Telescopes are instruments for collecting radio waves from outer space objects. The wave is reflected from a parabolic dish towards an aerial plane situated at the center. The signals are led onto a radio receiver.

The wavelength of radio waves is very large (from 0.3 mm to 30 cm). The radio telescope, having an aperture comparable to the optical telescope, has a very poor resolution. A considerable increase in resolution can be gained with the use of an interferometer.

A collection of the same antennae that is spaced at regular intervals will show that the elevation angle of a celestial object can be calculated. It can be computed from the time difference as well as the distance between the receivers. The angular separation can travel from the difference of the elevation angles and equal to the resolution of the time difference.

Hence, scientific instruments are devices made in order to assist in conducting Science. Examples would be found in a chemistry or biology laboratory. This includes:

• test tubes
• glass wares use for experiments and others