1 Introduction to Observation 2 Telescope 3 Observatory and Telescope

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Telescope

Yudhiakto Pramudya, Ph.D

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1 _{Introduction to Observation}

2 _Telescope

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Dark adaptation

1 the pupils will dilate so allowing more light to enter the eye 2 the dark adaptation mechanism takes about 20 minutes to come

into effect.

Without high light levels reaching the retina, vitamin A is converted first to retine and then into rhodopsin that significantly improves sensitivity of the rods and cones which are the light sensitive receptors in the retina of the eye.

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Software : Stellarium, Celestia, Starry Night, Your Sky Weather : BMKG, cleardarksky

Compass, Star Map, Flash Light Log Book : observation report

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Report :

1 Time

2 Date

3 Location

4 Telescope type, focal length, focal ratio, eyepiece, magnification, etc 5 Your target, may include sketch or image

6 note of local weather

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A telescope is used to do three things:

1 To collect more light so that fainter obejects can be seen beter than

with unaided eye.

2 To enable us to see greater detail in a distant object. 3 to gain resolution

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Telescope classes :

1 Refractors, which use lenses to gather light 2 Reflectors, which use mirros

3 Catadioptric system, which use a combination of lens and mirror

The Objective : the main light-gathering component.

The greater its area, the greater the amount of light received. f-ratio : the ratio of its focal length (F) to its diameter (D)

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Fundamental limit to the detail in the image is the effects of diffraction. Assuming that the telescope has a circular aperture, then the image formed by a point source is a central disc surrounded by a number of concentric rings rapidly decreasing in brightness.

θ= 1.22λ/D ₍₁₎

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If one consider a 150 mm telescope observing in green light of

The resolution is limited by seeing - a function of turbulence in the atmosphere.

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Ocular : A lens that we use to view an image formed by the objective. In a reflector telescope, the objective is a mirror (primary). The

secondary is another mirror to direct the reflected beam from primary to a better position for viewing.

Catadioptric telescopes, such as the Schmidt and Maksutov systems, have a mirror with a spherical curve.

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Binoculars are good for scanning wide areas of sky and viewing the Moon. The image is upright and visible with both eyes.

True binoculars have a pair of prisms in each optical path. They are classified by a pair of number

for example : 15x70

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The mounting is intended to

1 hold the telescope 2 keep it steady

3 enable the observer to keep it pointed at a celestial object as Earth

rotates.

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axis) and the declination axis.

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Magnification

M ₌ fobj

f_ocu (2)

To enhance the magnification, we can use Barlow lens.

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Hubble Space Telescope (HST) was launched in April 1990 to observe universe over a wavelength range that extends from the UV through the visible to the near infrared (0.12µmto 2.4µm).

The HST’s primary mirror is 2.4 m across so that in green light its angular resolution is given by:

∆θ= 1.22λ/D= 1.22x5.1x10_2.4−7rad

∆θ= 0.053arcsec