atmosphere earth astronomical-instruments

8/20/2019 Atmosphere Earth Astronomical-Instruments

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Astronomical

Instruments


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• Troposphere (8-15 km): 3-5 kmresponsible for earth’s weather

• Stratosphere: 25-35 km, homogeneosan! "onstant temperatre# Two la$ersare there# %ower "ontains Slphate an!thoght to pla$ role in rainfall# &pperla$er forms 'one la$er where most ofthe & blo"ke!#

• *esosphere: 5+-8+km# *eteors fromoter spa"e "ome an! brn#

• onosphere: 8+km -3++km# la$er (8+-

12+km, refle"ts longer ra!io wa.es), /la$er (12+km-2++km, refle"ts me!imra!io wa.es), 01(2++-3++km), 02(3++km, refle"ts short ra!io wa.e)# Stillmeter, "entimeter mi"rowa.es "an pass

nhin!ere!#


3/17

Electromagnetic radiation


4/17

'nl$ following wa.elength ranges rea"h the /arthnhin!ere!:

• Optical window: +++ 2++ 4+

• Radio window: 3mm- 5+ meters

• Infrared window: 8 -1 µm

elow 3+++ 4+ ra!iation is "ompletel$ blo"ke!# i,e,

• & (3+++ 4+ 3++ 4+) blo"ke!

• 6- ra$s (3++ 4+ - +#1 4+) blo"ke!

• γ - ra$s (less than +#1 4+) blo"ke!


5/17

• Study of IR: 7 is absorbe! "hiefl$ b$ water an! '2, mostof whi"h is below 3+ km# This height "an be e9"ee!e! b$Stratospheri" balloons#

• Study of UV: 4bsorbe! at m"h higher altit!e an! "ol!be e9plore! b$ the ro"kets# '3 la$ers in stratosphere forms!e to the a"tion of & ra!iation from Sn on o9$genmole"les an! absorbs the wa.elength region 2++-22++

4ngstrom# '2 mole"le absorbs 22++-++ 4ngstrom, most ofthem at 1++km# ;2, ', ; absorbs at 5++ 4ngstrom < 2+km#


6/17

Optical telescopes'pti"al teles"ope of two t$pes

a# 7efle"ting teles"ope

b# 7efra"ting teles"ope

=roperties of teles"opes !epen!s on:

Magnifying power

(>) ? 0@f

where, 0?fo"al length of the obAe"ti.e an! f? fo"al length of thee$epie"e#

/9ample: > of a teles"ope of 0?B++C (e#g#, the 12+ in"hrefle"tor at %i"k) an! sing an e$epie"e of f? 1C is B++#


7/17

Brightness of Image

• %ight gathering power of a lens or a mirror is proportional to thesDare of its apertre# Ths more an! more faint obAe"ts "ol! beobser.e! with teles"ope with larger apertres#

• 0or e9ten!e! obAe"ts like moon, planets an! neblae, thebrightness of the image !epen!s on apertre as well as fo"al

length of teles"ope#

• 4rea of the image of an e9ten!e! obAe"t forme! at the fo"s isproportional to the sDare of the fo"al length#


8/17

Resoling power

%imits of resoltion ? #5@a se"on!s of ar"

Enown as awes rle#/9ample: 0or 2++C (a) refle"tor, it is+#+225, means two stars separate! b$+C#+225 will be resol.e!#

f!a ratio

• %ight gathering power !epen!s on Fa’ an! sie of the image!epen!s on Ff’# So fo"al ratio will, in general inflen"e thebrightness of the image#

• %arge fo"al ratio means sprea!ing of the image o.er larger area#%arge refle"tor it is 3-5# 0or 2++C Gale refle"tor it is 3#3 an!e9presse! as f@3#3#


9/17

"ypes of reflecting telescopes


10/17

Refracting telescope


11/17

Relatie adantages of reflectors andrefractors

1# 0or the refra"tors mirror shol! be homogeneos an! for therefle"tor me"hani"all$ homogeneos mirror wol! be fine#

2# hromati" aberration of lens seriosl$ affe"ts the Dalit$ ofphotographi" an! spe"tros"opi" works#

3# f the mirrors being perfe"tl$ a"hromati", high Dalit$ is alwa$sa"hie.e! b$ refle"tor#

# Small !ifferen"es of temperatres of !ifferent parts of a largemirror often !e"rease the !efining power of the mirror# 'bAe"ti.elenses of a refra"tor being m"h smaller in sie, !iffi"lt$ ne.erbe"ome serios for the refra"tor# So refra"tor ha.e wi!e fiel! ofgoo! !efinition#

5# 0or the same sie of apertre refra"tors are most "ostl$ than therefle"tors#

B# 0or .isal obser.ations an! measrements refra"tors are wi!el$ se!#


12/17

1# 'bAe"ti.e prism spe"trographs "an onl$ be se! in refra"tors#

2# 0or =hotograph$, spe"tros"op$, photoele"tri" photometr$,

et"# the large refle"tors are se!#

3# 0or the faint obAe"ts large refle"tors are essential


13/17

#u$$le Space "elescope

The Gbble Spa"e Teles"ope (GST) is a spa"e teles"ope that was"arrie! into orbit b$ a Spa"e Shttle in 1+ an! remains inoperation# 4 2#-meter (# ft) apertre teles"ope in low /arthorbit, GbbleHs for main instrments obser.e in the near

ltra.iolet, .isible, an! near infrare! spe"tra#


14/17

Radio telescopes


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0or %i"k 12+ in"h refle"tor at B+++ 4ngstrom wa.elength the limit ofresoltion obtaine! will be

Same law wol! be applie! to ra!io wa.es# Sppose 21 "m wa.esare obser.e! with the 25+ feet paraboli" refle"tor at Io!rellank, resoltion a"hie.e! in this "ase will be gi.en b$

So, resoltion is 1++++ times poorer e.en for wa.elength in shortersi!e an! a !ish of almost ma9imm sie#


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%MR" telescope


17/17

A&MA telescope

atmosphere earth astronomical-instruments

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