INTRODUCTION TO BASIC

OBSERVATIONAL ASTRONOMY

 

WHETHER NAKED EYE, BINOCULARS OR USING A TELESCOPE THE FOLLOWING BASIC KNOWLEDGE AND SKILLS ARE REQUIRED.

 

1.          DARK ADAPTION

 

ALLOW THE EYES 20 MINUTES OR MORE TO ADJUST TO DARKNESS IN ORDER TO BECOME SENSITIVE TO FAINT LIGHT.

 

A DIMMED (RED CELLOPHANE) TORCH WILL PROVIDE ENOUGH LIGHT WHEN DARK ADAPTED.

 

2.         AVERTED VISION

 

LOOKING SLIGHTLY TO THE SIDE OF A FAINT OBJECT, INSTEAD OF DIRECTLY AT IT, GIVES A MUCH IMPROVED VIEW, BECAUSE THE RETINA IS MOST LIGHT-SENSITIVE AROUND THE EDGES.

 

IT IS ALSO IMPORTANT TO MOVE THE EYES AS AN IMAGE ON THE RETINA BECOMES IGNORED BY THE BRAIN AFTER A TIME.

 

3.         LIMITING MAGNITUDE

 

THE BRIGHTNESS OF THE FAINTEST STAR THAT CAN BE SEEN ON A GIVEN NIGHT.

 

A DARK ADAPTED NAKED EYE HAS AN APERTURE OF ABOUT 7MM (THE PUPIL) SO STARS TO ABOUT MAG. 6 CAN BE SEEN.

 

BINOCULARS (50MM APERTURE) – MAG. 10

OBSERVING FAINT OBJECTS IS A SKILL, THE EYE-BRAIN SYSTEM BENEFITS FROM PRACTICE AND EXPERIENCE.

 

A SKILLED OBSERVER UNDER DARK SKIES CAN SEE AS MUCH AS TWO MAGNITUDES FAINTER THAN A NOVICE.

MAGNITUDE LIMITS

 

MAG. LIMIT                NO. OF STARS         DESCRIPTION

 

2.5                                        93                                   IN CRUX ONLY 3 STARS SEEN

                                                                                               

3.5                                         283

 

4.5                                        893                                 N.E. FROM CITY

 

5.0                                                                               N.E. IN AVERAGE SKIES

                                                                                               

5.5                                        2822                               N.E. IN BEST SEMI-DARK SKIES

                                                                                               

6.5                                        8768                               N.E. FROM RURAL SKIES

 

7.5                                     26533                    BINOCULAR LIMIT WITHIN CITY

 

10.0                                                                  BINOCULAR LIMIT IN BEST SEMI-DARK SKIES

                                                                                               

10.5                                    ~60 000                 BINOCULAR LIMIT IN VERY   DARK SKIES

                                                                        15CM TELESCOPE IN CITY

 

11.5                                    ~180 000                LIMIT OF 60MM TELESCOPE

 

12.5                                    ~540 000               15CM TELESCOPE FROM SEMI-DARK SKIES

 

ANGULAR SEPARATION

 

DISTANCES IN THE NIGHT SKY ARE MEASURED IN DEGREES (OR FINER DIVISIONS).

 

·              FIST AT ARM’S LENGTH         10Ί

 

·              A FINGERTIP               1Ί

 

A DEGREE IS DIVIDED INTO 60 ARC MINUTES (’) THE SUN AND MOON ARE EACH ½Ί OR 30’.

 

ONE ARC MINUTE IS DIVIDED IN 60 ARC SECONDS (”).

 

E.G.

 

JUPITER’S DISC IS 40” ACROSS IF VIEWED WITH 7-POWER BINOCULARS THE DISC APPEARS TO BE 7 X 40” = 280” RENDERING IT VISIBLE AS IT NOW EXCEEDS THE RESOLUTION OF THE NAKED EYE WHICH IS 60”.

 

RESOLVING POWERS

 

 

APERTURE                                                   RESOLUTION

 

NAKED EYE                                                                           60”

60MM                                                                                    2.3”

90MM                                                                                    1.6”

15CM (6 INCH)                   0.93”

20CM (8 INCH)                  0.70”

25CM (10 INCH)                 0.56”

OTHER RESOURCES

FOR BASIC OBSERVING

 

1.       LEARN BRIGHT STARS AND CONSTELLATIONS

 

2.      DETAILED STAR CHARTS

         E.G. 

·              SKY ATLAS 2000 – TIRION DETAILS STARS TO MAGNITUDE 8

·              43 000 STARS

·              2 500 CLUSTER, NEBULAE, GALAXIES.

 

3.      COMPUTER PROGRAMS

         E.G.

·              CYBERSKY – 8403 STARS TO MAG. 6.5

·              STARRY NIGHT PRO – 19 MILLION STARS TO MAG 16.5

 

4.      ACCURATE TIME

         E.G.

·              NEEDED FOR TIMING LUNAR OCCULTATIONS, CRATER TIMINGS DURING LUNAR ECLIPSE.

AREAS OF OBSERVATIONAL

ASTRONOMY

 

SOLAR OBSERVING

 

·              MONITOR SUN SPOT ACTIVITY

 

LUNAR OBSERVING

 

·              LUNAR FEATURES

·              ECLIPSES

·              LUNAR OCCULTATION (TOTAL AND GRAZING)

 

PLANETARY OBSERVING

 

·              INCLUDING PHENOMENA OF GALILEAN MOONS, ECLIPSES, TRANSITS, OCCULTATIONS

·              MINOR PLANETS (ASTEROIDS)

 

COMETS

 

·              METEOR SHOWERS

 

STARS

 

·              DOUBLE STARS

·              VARIABLE STARS (OVER 30 000 KNOWN, HOWEVER, LESS THAN 400 ARE PRESENTLY BEING OBSERVED FROM SOUTHERN AFRICA).

 

DEEP SKY

 

·              GALAXIES

·              STAR CLUSTERS

·              NEBULAE (BRIGHT, REFLECTION, PLANETARY)

·              DARK NEBULAE

·              GLOBULAR CLUSTERS

 

OTHER INTERESTING AREAS

 

·              ASTROPHOTOGRAPHY

 

·              TRACKING ARTIFICIAL SATELLITES, EG. ISS, HST

INCLUDING IRIDIUM COMMUNICATION SATELLITES THAT CAN PRODUCE SPECTACULAR FLARES (MAG. –8) WHEN THE SUN GLINTS OFF THEIR SHINY SURFACES.