The beginning... When do you think the first usage of radio waves was? What was the first piece of technology to use them?

Transcription

1 The beginning... When d yu think the first usage f radi waves was? What was the first piece f technlgy t use them?

2 The beginning... - It all starts with math - James Clerk Maxwell, in 1864, shwed using mathematics that electrmagnetic frce culd be prpagated thrugh free space at any wavelength He als went n t calculate the speed f light t within 4% f what we knw tday! - Wasn't until 1888 that Heinrich Rudlf Hertz demnstrated in the lab that electrmagnetic waves existed by prducing and detecting radi waves

3 First uses: - Wireless telegraph It is nt very clear as t whm t credit with the verall inventin f this device. First device t be used t successfully transmit a transatlantic message was invented by Guglielm Marcni. Just like the regular telegraph machines, the wireless versin als sent infrmatin using Mrse Cde.

4 Radi's Evlutin: - Sn after messages were successfully sent via Mrse cde, it was hypthesized that speech infrmatin culd be encded and sent via radi waves. This was achieved by Reginald Fessenden by Amplitude Mdulatin (AM radi) in

5 Radi's Evlutin: - After Wrld War I, AM Radi tk ff thanks t the cmpany RCA - AM lingered arund fr awhile until the 1930s when amatuer radi peratrs started experimenting with frequency mdulatin FM Radi gets its fficial start in 1933 thanks t Edwin Armstrng 1938 marks the famus Orsn Welles bradcast f "The War f the Wrlds"

6 Things take ff... - TV gets invented arund the 50s and "Radi" starts t take a backseat TV bradcasts als rely n radi waves! - At this pint a lt f things start t happen including the transistr radi, radi satellites, and its cnversin int the digital age (all yur technlgies rely n the transmissin and receptin f radi waves!) - The imprtant thing is hw radi waves started t be used in astrnmy in the 1930s...

7 Interlude: A gd breakdwn f the histry f Radi:

8 Radi Astrnmy: - The histry f Radi astrnmy again starts with Maxwell and Hertz - Frm these predecessrs, many scientists believed they culd detect radi emissins frm celestial bjects 2 ntable scientists wh experimented with this early n were Thmas Alva Edisn and Sir Oliver J. Ldge in the 1890's.

9 Karl Jansky: - In the early 1930s Karl Jansky was assigned by the Bell Telephne Cmpany t investigate surces f static that might interfere with radi transmissins. - Jansky build an antenna that detected radi waves f 20.5 MHz.

10 Karl Jansky cnt. - Using his antenna, Jansky discvered three static surces: 1. Nearby thunderstrms 2. Distant thunderstrms 3. an unknwn hiss that ccurred apprximately nce a day... - What was that unknwn hiss?

11 Karl Jansky cnt. - It turns ut, the faint hiss that Jansky discvered wasn't fllwing the 24-hr day f the sun, therefre wasn't cming frm the sun. Instead it fllwed a sidereal day (23 hrs. 56 mins) which fllwed the path f a distant star Turned ut he discvered the radi emissins f the center f ur galaxy His results f this were widely publicized in 1933, but sadly he never wrked in radi astrnmy again

12 Grte Reber: - Was very interested in Jansky's discvery in 1933, but was unable t get a jb at an bservatry due t it being the great depressin - He decided that wasn't ging t stp him: Built his wn (very impressive) radi telescpe in his backyard

13 Grte Reber cnt. - His telescpe used a parablic dish design Fcuses all wavelengths t a single fcus - After many attempts, he cnfirmed Jansky's discvery in Overall, he used his telescpe t chart the night sky and keep track f the "brightness" f radi waves in ur galaxy Used these t make the first "pictures" using radi waves in the frm f cntur maps (based n the brightness f the radiatin detected)

14 Imprtant times in Radi Astrnmy: : James Stanley Hey successfully detects radi emissins frm the sun : Jan Ort and his student Hendrik C. van de Hulst predict the existence f the 21-cm hydrgen line (huge in astrchemistry) : Edward Mills Purcell and Harld Irving Ewen discver the 21-cm hydrgen line

15 Other imprtant times: - In the 1940s radi interfermetry was used t perfrm the first high reslutin radi astrnmy bservatins : First VLBI (Very Lng baseline Interfermetry) dne by Canadian and U.S. researchers Frm this pint it was realized VLBI culd be used t perfrm many useful tasks in radi astrnmy - Frm this pint n, VLBI has been n the dminant techniques in the field f radi astrnmy as it allwed fr greater and greater reslutin as the baselines became greater and greater

16 Mre Dates: : the largest radi telescpe t date is built in Arecib, Puert Ric (1000-ft. aperture)

17 Mre Dates: and 1967: Shapir's 4th test The '4th' test f Einstein's general relativity dne at Haystack Observatry

18 The VLA:

19 Lcal Effrts: - A lt f imprvements in radi astrnmy wuldn't have happened if it wasn't fr the effrts f MIT's Radiatin lab during and after WWII Befre, during and after the war, the military invested a lt f research mney int the develpment f better radar systems.

20 Lcal Effrts cntinued: - These tw surces d a gd jb shwing the rle MIT's Rad lab played in the war effrts: Milestnes:MIT_Radiatin_Labratry%2C_

21 Pst-War effrts: - During the Cld War, great emphasis was placed n lng range detectin f ICBMs At the time, radar nly wrked a maximum distance f the hrizn Made it necessary fr much lnger range f detectin Military again gave much f the refining wrk t MIT, this time at Lincln Labs:

22 Hw research is dne: - The previus links are perfect examples f hw research is dne in the scientific cmmunity: The gvernment / military see shrtcmings in technlgy Research mney is given ut t figure ut hw t imprve the technlgy (the mre pressing, the mre mney) rinse and repeat...

23 Example: - Military needs a lnger range radar fr ICBM detectin: Lincln Labs given R&D mney and develps SAGE - Military ntices a lt f false alarms due t insphere and aurras: MIT finds ut what is causing these and figures ut hw t fine-tune the system - The imprvements nt nly beneficial fr the military, but fr the scientific cmmunity as a whle

24 There is s much mre... But nt enugh time t cver it all! If yu are interested, lk up research dne in: - Incherent Scatter Radar (Space Weather) - Sgr A* r NGC4258 (Black Hles!!!!) / - Event Hrizn Telescpe - Gedesy (plate tectnics) - VLBI - Astrchemistry (spectrscpy, chemicals in space, etc.) - MASERs (basically radi lasers, everyne lves lasers!)