WHAT CAN ASTRONOMERS MEASURE WITH LIGHT? TEMPERATURE OF A STAR ELEMENTS PRESENT IN A STAR

1. Do not anticipate trouble, or worry about what may never happen. Keep in the sunlight. - Benjamin Franklin -

2. WHAT CAN ASTRONOMERS MEASURE WITH LIGHT? • TEMPERATURE OF A STAR • ELEMENTS PRESENT IN A STAR • DISTANCE • AGE OF STARS • SPEED

3. WHY CAN’T YOU READ THE WRITING ON A DOLLAR BILL AT 100 METERS?

4. WHY CAN’T YOU READ THE WRITING ON A DOLLAR BILL AT 100 METERS? THE DOLLAR DOES NOT TAKE UP ENOUGH SPACE ON YOUR EYE’S SCREEN (RETINA). THE IMAGE DOES NOT COVER ENOUGH RECEPTOR CELLS (RODS AND CONES). THINK ABOUT A DIGITAL CAMERA - THERE WOULD NOT BE ENOUGH PIXELS TO COVER THE IMAGE. WE NEED TO MAKE THE IMAGE LARGER.

5. THAT IS WHY WE USE TELESCOPES. TELESCOPES CAN BE CONSTRUCTED TO USE RADIATION FROM X-RAYS ALL THE WAY OUT TO RADIO WAVES. IN THE VISIBLE REGION OF THE SPECTRUM, WE USE TWO KINDS OF TELESCOPES: REFRACTORS REFLECTORS

6. THE INVENTION OF THE TELESCOPE IS OFTEN CREDITED TO HANS LIPPERSHEY IN 1608. GALILEO IS FIRST CREDITED WITH USING THE TELESCOPE IN 1609 TO STUDY THE SKY. HE BUILD AN IMPROVED VERSION OF THE TELESCOPE AND PUBLISHED HIS FINDINGS IN 1610 IN A BOOKLET CALLED “THE STARRY MESSENGER.”

7. REFRACTORS ARE BASICALLY A LONG TUBE WITH AN OBJECTIVE LENS IN FRONT. THE OBJECTIVE LENS GATHERS LIGHT AND FOCUSES IT TOWARDS THE BACK OF THE TUBE. THE EYEPIECE BRINGS THE IMAGE TO YOUR EYE AND MAGNAFIES IT.

8. IT IS DIFFICULT TO MAKE LARGE OBJECTIVE LENSES. DIFFERENT COLORS OF LIGHT CAN BE REFRACTED (BENT) DIFFERENTLY. THESE PROBLEMS CAN BE OVERCOME USING A REFLECTING TELESCOPE. A CURVED MIRROR IS USED RATHER THAN AN OBJECTIVE LENS.

9. THE SHORTEST WAVELENGTHS OF LIGHT THAT CAN BE FOCUSED IN A TELESCOPE ARE X-RAYS. CONCENTRIC TUBES WITH CURVED SURFACES ARE USED AS LENSES. THEY HAVE TO BE USED ABOVE THE EARTH’S ATMOSPHERE.

10. THIS TECHNOLOGY IS USED WITH THE CHANDRA X-RAY TELESCOPE. THE CHANDRA TELESCOPE SATELLITE PROBE IS THE LARGEST SATELLITE LAUNCHED BY THE SHUTTLE AND IS 45 FEET LONG. IT WAS LAUNCHED IN 1999 FROM SPACE SHUTTLE COLUMBIA.

11. AT THE OTHER END OF THE SPECTRUM AT LONG WAVELENGTHS ARE RADIO TELESCOPES. THEY WORK LIKE REFRACTING TELESCOPES WITH THE DISK ACTING LIKE A MIRROR.

12. TECHNIQUES ARE AVAILABLE TO LET A NUMBER OF RADIO TELESCOPES WORK TOGETHER AS ONE LARGE TELESCOPE. THAT SAME TECHNIQUE HAS RECENTLY BEEN APPLIED TO OPTICAL TELESCOPES. VERY LARGE ARRAY - NEW MEXICO

13. TELESCOPES OFFER ASTRONOMERS CERTAIN ADVANTAGES: CAN SEE MORE DETAILS (MAGNIFICATION) CAN GATHER LARGE AMOUNTS OF LIGHT TO SEE DIM OBJECTS CAN MAKE TIME EXPOSURES CAN MEASURE LIGHT AT DIFFERENT WAVELENGTHS

14. FOR A CIRCULAR TELESCOPE, THE COLLECTING AREA IS r2, WHERE r IS THE RADIUS OF THE COLLECTING LENS. IF ONE TELESCOPE’S RADIUS IS TWICE AS LARGE AS ANOTHER, IT WILL COLLECT 4 TIMES AS MUCH LIGHT. HOW MUCH MORE LIGHT WILL A VISIBLE LIGHT TELESCOPE WITH A RADIUS OF 5 M COLLECT THAN A HUMAN EYE THAT HAS A PUPIL WITH A 1 mm RADIUS?

15. UNITS IN ASTRONOMY: ASTRONOMICAL UNIT, AU - DISTANCE FROM EARTH TO SUN - 93,000,000 MILES = 149 X 106 km LIGHT YEAR - THE DISTANCE LIGHT CAN TRAVEL IN ONE YEAR = 5,878,625,373,183.61 statute miles OR ~6 X 1012 mi = 9,460,730,472,580.800 km OR ~ 10 X 1012 km