Astronomy

7/17/2019 Astronomy

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ASTRONOMY ----- AN OVERVIEW

Prof. K. Shankara Sastry.

Dept. of Astronomy Ret!"#

Osman$a %n$&ers$ty

Intro!'(t$onAstronomy $s the o)!est s($en(e. Ve!$( astronomy has a )on* span start$n*

from ant$+'$ty. Astronom$(a) top$(s are ment$one! $n &e!$( )$terat're. An

an($ent report on (on,'n(t$on of 'p$ter $th the star δ (an(r$ $s fo'n! $n

Ta$tt$reeya samh$ta an! other te/ts. There are an($ent o0ser&at$ons of moon

re(or!e! $n R$*&e!a. S'(h re(or!s are a&a$)a0)e $n ora) tra!$t$ona) )$terat'reof &e!$( t$mes. There as no systemat$(te/t (omp$)e! pr$or to 1233 45

Pro0a0)y Ve!an*a yot$sha (omp$)e! 0y 6a*a!ha $n 173345 $s one of the

ear)$est te/ts. Astronomy te/ts (a))e! S$!!hantas essent$a))y !ea) $th

P)anetary mot$ons# the$r per$o!s of mot$on# re)at$&e s$8es of the Earth# the S'nan! the Moon an! (omp'tat$on of e()$pses of the S'n an! the Moon. Th's the

p)anetary astronomy ha! f)o'r$she! $n In!$a start$n* from Arya0hata I $n the

9th(ent'ry AD to 4haskara II $n the 17th(ent'ry AD. Arya0hata (ompose! an

astronom$(a) te/t $n2:;AD (onta$n$n* ta0)es of astronom$(a) (onstants# s$neta0)es an! (omp'tat$on of )on*$t'!es of p)anets. <e e/p)a$ne! the !a$)y

mot$on of the Earth# !'rat$on of !ay an! n$*ht an! the )en*th of the year.

Arya0hata propose! S'rya S$!!hanta a((or!$n* to h$(h the S'n $s at the

(entre of the (osmos. A((or!$n* to &e!$( )$terat're# S'rya S$!!hanta

as f$rst re&ea)e! 0y S'n *o! h$mse)f to May'ras'ra. Astronomy has 0eenfas($nat$n* to the peop)e a)) o&er the or)! s$n(e a )on* t$me. The =reek

astronomer Pto)emy a0o't 193 AD" (omp$)e! a ser$es of 1> &o)'mes $n

astronomy knon as ?A)ma*est@. A((or!$n* to Pto)emy# the Earth $ss'ppose! to 0e at the (entre of the %n$&erse an! the S'n# Moon an! the then

knon p)anets Mer('ry# Ven's# Mars# 'p$ter an! Sat'rn mo&e! aro'n!

the Earth $n ($r()es. Th$s theory (a))e! =eo (entr$( theory pre!om$nant)y

pre&a$)e! from 1st to 19th (ent'ry. Ara0s e/ten!e! the ork of Pto)emy. They

0ro'*ht <$n!' system of n'm0ers to E'rope. In the year 192> 5opern$('s a

*reat astronomer ho )a$! the fo'n!at$on for the mo!ern p)anetary astronomys'**este! that S'n $s at the (entre of the (osmos an! p)anets $n()'!$n* the

Earth mo&e! aro'n! the S'n. Th$s <e)$o (entr$( theory# or$*$na))y propose! 0y Arya0hata as *ra!'a))y a((epte! 0y m$! 1:th (ent'ry. After 5opern$('s#

the *reat o0ser&at$ona) astronomer Ty(ho 4rahe 192; 1;31 AD" ma!e

a(('rate o0ser&at$ons of p)anetary pos$t$ons an! h$s ass$stant ohannes

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Kep)er 19:1 1;>3 AD" st'!$e! these o0ser&at$ons an! form')ate! the

three famo's )as of p)anetary mot$on. A((or!$n* to these )as# the

p)anets re&o)&e aro'n! the S'n $n e))$pt$(a) or0$ts $th the S'n at one fo('sB

the )$ne ,o$n$n* the S'n seeps e+'a) areas $n e+'a) $nter&a)s of t$meB an! the

per$o! of re&o)'t$on of a p)anet $s !$re(t)y re)ate! to P)anetCs mean !$stan(efrom the S'n. 6ater S$r Issa( Neton 1;27 1:7: AD" st'!$e! the )as of

Kep)er an! !$s(o&ere! the (e)e0rate! )a of %n$&ersa) =ra&$tat$on. M'(h

ear)$er to Neton# the EarthCs *ra&$ty as s'ppose! to 0e pre!$(te! 0y4haskara(harya of 17th (ent'ry. NetonCs )a of *ra&$tat$on a)on* $th h$s

7n! )a of mot$on mass a((e)erat$on For(e" forms the 0as$s for 5e)est$a)

Me(han$(s. The !$s(o&ery of the p)anet Nept'ne $s an e/amp)e for the

app)$(at$on of NetonCs )a of *ra&$tat$on to 5e)est$a) Me(han$(s. The

p)anets Mer('ry# Ven's# Mars# 'p$ter an! Sat'rn ere knon from ant$+'$ty.

<ers(he) !$s(o&ere! %ran's $n 1G th (ent'ry $th a te)es(ope. Mot$on of%ran's (o')! not 0e e/p)a$ne! 0y tak$n* $nto a((o'nt the attra(t$on

of a)) p)anets knon at that t$me. From pert'r0at$on theory of (e)est$a)me(han$(s the mathemat$($ans 6a&err$er $n Fran(e an! A!ams $n En*)an!

$n!epen!ent)y (a)(')ate! the pos$t$on of a ne P)anet at (erta$n t$me. They

aske! the o0ser&er =a))e $n =ermany to !$re(t h$s te)es(ope to th

e pre!$(te! pos$t$on. =a))e a((or!$n*)y fo'n! the ne P)anet

Nept'ne at the pre!$(te! pos$t$on. Th

$s !$s(o&ery as ma!e $n the 1H

th

(ent'ry.

Re)at$onsh$p $th other

0ran(hes of S($en(e

Astronmy $s not on)y o)!est s($en(e 0't $t $sa)so ()ose)y re)ate! to other 0ran(hes of

S($en(e phys$(s# mathemat$(s# 0$o)o*y an! (hem$stry. Astrophys$(s !ea)$n*

$th the

app)$(at$on of the )as of phys$(s to 'n!e

rstan! the nat're of the p)anets# stars an!*a)a/$es an! the 'n$&erse as a ho)e $s an $n

separa0)e part of astr

onomy. The pr$n($p)esof opt$(s an! e)e(tron$(s of phys$(s are the

0as$s for astronom$(a) te

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)es(opes. Photometr$(

an! Spe(tros(op$( te(hn$+'es of phys$(s are the

0as$s for the st'!y of str'(t're of stars

an! *a)a/$es. Pr$n($p)es of stat$st$(a) me(han$(s an! +'ant'm me(han$(s are

e/tens$&e)y'se! $n theoret$(a) astronom$(a) st'!$es.

As a)rea!y state!# (e)est$a) me(han$(s h$(h !ea)s $th the pro0)ems of

p)anetary mot$on$s 0ase! on f'n!amenta) )as of phys$(s

name)y NetonCs )a of *ra&$tat$on an! the 7n!

)a of mot$on. 5e)est$a) Me(h

an$(s $s $nt$mate)y

re)ate! to spa(e f)$*hts. Astronomer Mathemat$($ans =a'ss# 6ap)a(e

an! others !e&e)ope! n'mer$

(a) metho!s to so)&e some

(omp)$(ate! e+'at$ons $n (e)est$a) me(han$(s.

Thermo n'()ear rea(t$ons ere !$s(o&ere! from the st'!y of

Ste))ar str'(t'res# as the

stars *enerate the ener*y (h$ef)y 0y (on&er

s$on of hy!ro*en to he)$'m thro'*h proton- proton an! (ar0on-n$tro*en (y()es. Re(ent)y

a n'm0er of mo)e(')es an! ra!$(a)s are

!$s(o&ere! $n the atmospheres of stars# p)anets# (omets an! $n the $nterste))ar

spa(e. Thee)ement <e)$'m as f$rst fo'n! $n the So)ar

spe(tr'm o0ta$ne! from the o0ser&at$ons of

the tota) So)ar e()$pse of A'*'st 1G#1G;G from

the To0a((o f$e)!s of ='nt'r $n An!hra

pra!esh. More re(ent)y# F)'or$ne h$(h $s 'se!$n o'r !a$)y tooth paste $s fo'n! to 0e

pro!'(e! !'r$n* (erta$n sta*es of e&o)'t$on $n

some stars. These f$n!$n*s re&ea) the )$nk 0eteen (hem$stry an! astronomy. Re(ent)y tr

a(es of e/tra terrestr$a) )$fe an! some

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or*an$( mo)e(')es ha&e 0een !$s(o&ere! on Mars an! e)sehere $n o'ter

spa(e. Th$s

$nterest$n* res')t has prompte! e&en 0$o)

o*$sts to ork $th the astronomers to

'n!erstan! the or$*$n of )$fe. En*$neer$n* sk$))sare 'se! $n spa(e f)$*hts. Th's astronomy

$s a (ommon *ro'n! for s($ent$sts from a)) 0ran

(hes of 0as$( an! app)$e! s($en(es to(o))a0orate.

S(ope Of Astronomy

We st'!y astronomy to 'n!erstan! the 'n$&erse as

a ho)e# $n a)) respe(ts. The 'n$&erse

$s &ery &ast an! (onta$ns enor

mo's +'ant$ty of matter. It (an 0e !$&$!e! $nto se&era) parts

for the p'rpose of !es(r$pt$on.1" The so)ar system (ompr$s$n* the S'n the P)anets an! the$r sate))$tes#

astero$!s#

(omets an! $nterp)anetary me!$'m.

7" F'rther o't are stars that o(('r as s$n*)e# $n pa$rs an! m')t$p)es.

>" The stars a)so form *ro'ps an! ()'sters an! 0$**er systems (a))e! *a)a/$es

)$ke

o'r home *a)a/y# the M$)ky Way *a)a/y.2" The $nter ste))ar spa(e $.e. the spa(e

0eteen the stars (onta$n$n* !'st an! ()o'!s

an! *as an! ne0')ae

9" 6ar*e s(a)e str'(t'res s'(h as ()'sters

of *a)a/$es an! s'per ()'sters of *a)a/$es.

In or!er to !es(r$0e the 'n$&erse# one re+'$res )ar*e n'm0ers $n terms of

phys$(a)

parameters s'(h as )en*th# mass an! t$me. The a&era*e !$stan(e 0eteen the

S'n an! theEarth $s 193 m$))$on k$)ometres

an! )$*ht takes a0o't G1J>

m$n'tes to tra&e) th$s !$stan(e.

The !$stan(e 0eteen the S'n an! P)'to $n

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the so)ar system $s 9.9 )$*ht ho'rs here a

)$*ht ho'r $s the !$stan(e tra&e))e! 0y )$*ht $n

one ho'r $th the spee! of )$*ht at > )akh

k$)ometres per se(on!. The s$8e of a typ$(a)

star )$ke o'r S'n $s :33#333 k$)ometres an!the mass $s a0o't 7 13>>

*rams. <'*e systems )$ke *a)a/$es (onta$n enormo's +'ant$ty

of mass.

Stars

On a ()ear n$*ht sky e (an see a0o't ;333 star s of !$fferent (o)o'rs ran*$n* from 0)'e to

re! $th the nake! eye. We (an see a0o't 13333

stars $th a 0$no(')ar of fo(a) )en*th >to 2 $n(hes. The !$fferent (o)ors $n!$(ate !$ffe

rent phys$(a) (on!$t$ons $n the stars. 4)'e

stars are m'(h hotter# more mass$&e an! m'(h

yo'n*er h$)e re! ones are m'(h (oo)er

an! o)!er an! a)so )ess mass$&e. O'r S'n $s an ye))o type star. The masses ran*e from

3.1 so)ar mass to a0o't ;3 so)ar

masses an! s$8es ran*e from 1J

13 to 73 t$mes that of thes'n. The s'rfa(e temperat'res ran*e from

>333 to 23#333 !e*rees ke)&$n. The 0r$*ht stars

appear to form *ro'ps an! s'**est to 's f$*'

res of some an$ma)s or mytho)o*$(a) heroes.These *ro'ps are (a))e! 5onste))at$ons. Most

of the 5onste))at$ons ha&e the$r or$*$n

amon* 5ha)!eans an! =reek. There are no GG (onste))at$ons sprea! a)) o&er

the sky

To tho'san! years a*o =reeks re(o*n$se! 2G(onste))at$ons. 17 of th

e GG (onste))at$ons

)$e on the path of the earth or the apparent path of the S'n" an! the moon. These are

(a))e! o!$a( s$*ns or Rash$s. Ea(h rash$ $s 1;

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!e*rees $n $!th an! >3 !e*rees $n )en*th.

In In!$a nakshatras are 0e$n* 'se! from Ve!$( t$mes. There are 7: nakshatras

h$(h are

7: *ro'ps of stars )y$n* on or near the path

s of S'n an! Moon. In 5h$nese an! Ara0$(systems the (o'nterparts of nakshatras are

(a))e! 6'nar mans$ons or Man8$)s"# the ho'se

of the Moon. The$r n'm0er 7: (orrespon!s tothe s$!erea)per$o! of the moon h$(h $s

7:.>7 !ays. Th's the moon o(('p$es one mans$on ea(h !ay. As ea(h

nakshatra $s of

1>!e*rees 77m$n'tes the s'n $s $n ea(h naksha

tra for a0o't 1> !ays s$n(e the s'n mo&es

at a0o't 1 !e*ree per !ay. Th$s $s the 0as$s for nam$n* the !ay $n In!$a 0ynakshatra $n

h$(h the moon $s fo'n! at S'nr$se. Some $n!$&$!'a) stars ha&e prop

er names. Some of

the prom$nent stars amon* them are S$r$'s

Vyaa!ha"# 5anop's A*astya"# Po)estar

Dhr'&a"# A)ta$r Shra&ana"

# A)!e0eran Roh$n$" et(.

We sha)) no 0r$ef)y )ook $nto the e&o)'t$on of a star. A star $s a )'m$no's 0a)) of *ashe)! to*ether 0y *ra&$ty. Stars are 0orn

from ()o'!s of *as an! !'st 0y *ra&$tat$ona)

(ontra(t$on. D'r$n* (ontra(t$on#

*ra&$tat$ona) potent$a) ener*y $s

re)ease! an! ha)f of th$s

ener*y $s 't$)$se! $n heat$n* the star an! the rest $s ra!$ate! aay. Th's the

temperat're of

the (ontra(t$n* ()o'! $n(reases an! hen $trea(hes a0o't 13 m$))$on

!e*rees *ra&$tat$ona)

(ontra(t$on stops an! n'()ear rea(t$ons 0e*$n to

*enerate the ener*y. Th's a star $s 0orn

an! 0e*$ns to ra!$ate. In th$s pro(ess 2 <y

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!ro*en atoms (om0$ne to form a <e)$'m atom

0y f's$on an! the ener*y $s re)ease!. The n'()ear f's$on (ont$n'es an! more

an! more

hea&y e)ements are forme! an! the ener*y $s *enerate! 'nt$) a)) the n'()ear

f'e) $se/ha'ste!. The star 'n!er*oes se&era) (han

*es an! en!s 'p as a s'per !ense o0,e(t

name)y ah$te !arf# a ne'tron star or a 0)a(kho)e. The t$me re+'$re! for a star to rea(h

the f$na) sta*e &ar$es from a fe m$))$on years for a hot 0)'e star to a fe

0$))$on years for

a (oo) re! star. D'r$n* the f$na) sta*es of

e&o)'t$on some stars 'n!er*o &$o)ent e/p)os$ons

an! thro aay the$r mater$a) $nto $nterste))ar spa(e. S'(h stars are (a))e! No&ae or

S'perno&ae !epen!$n* on the $ntens$ty of the e/ p)os$on. When s'(h an e/p)os$on o(('rs#

the star 0e(omes so 0r$*ht that $t (an 0e seen e&en at !ay t$me. The f$rst

knon no&a as

seen $n 1392 AD as per the 5h$nese re(or!s. It

as so 0r$*ht that $t as seen for > eeks

!'r$n* !ay t$me. <oe&er s'(h

e/p)os$ons are rare.As a)rea!y ment$one! the stars en! 'p the$r )$&esas a s'per !ense o0,e(t# the )ess mass$&e

stars 0e(ome h$te !arfs

$th !ens$ty of the or!er of 139

to 13;

*mJ((. The mean

!ens$ty of Earth $s 9.9*mJ((. an! the mean !ens$ty of S'n $s 1.2*mJ((. It means that a

h$te !arf $s so !ense that a spoonf')) of

$ts matter o')! e$*h a ton on Earth.

5han!rasekhar# a renone! astr

ophys$($st shoe! $n 1H>9 that $f the mass of the h$te

!arf $s L1.2 t$mes the so)a

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rmass $t o')! 0e(ome 'nsta

0)e an! *o on (ontra(t$n*

$n!ef$n$te)y. Th$s $s (a))e! 5han!rasekharCs 6$m$t for the mass of a h$te

!arf. Stars

$th mass 0eteen G an! 73 so)ar masses en! 'p as ne'tron star

s h$)e those *reater than

a0o't 73 so)ar masses pro!'(e 0)a(k ho)es. The !ens$ty $n a typ$(a) ne'tron star $s aro'n!

1317

*mJ((. The$r ma/$m'm mass $s 7 to > so)ar masses an! ra!$'s $s 13

k$)ometers.

4)a(k ho)es ha&e a st$)) h$*her !ens$ty. A 0)a(k ho)e of one so)ar mass o')!ha&e a

ra!$'s of a0o't > k$)ometers

# h$(h means that the ent$re mass of the s'n $s s+'ee8e!

$nto a sphere of ra!$'s of mere > k$)ometers. If the Earth $s to 0e(ome a 0)a(k

ho)e $t hasto shr$nk $th a)) $ts mass ; / 1372

k*" to ra!$'s as sma)) as H mm from the presentra!$'s of ;333 k$)ometers. 5han!rasekha

r as aar!e! No0e) pr$8e $n 1HG> for h$s

o'tstan!$n* ork on h$te !arfs an! 0)a(k ho)

es. Some of these s'per !ense stars pa$r

$th a norma) star to form a 0$nary system. S'(h pa$rs em$t ra!$at$on of &ery

h$*h ener*y

$n -rays an! ')tr&$o)et re*$ons. A 0$nary

star $th a ne'tron star pro!'(es p')sar phenomena. In th$s# the ne'tron st

ar rotates &ery fast on $ts a/$s $th per$o!s of the or!er

of se(on!s to m$))$ se(on!s.

The shortest per$o! p')sar fo'n! so far has a per$o! of 1.9; / 13->

se(on!s. These o0,e(ts

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a)so em$t -rays. A pa$r of norma) star an! 0)a(k ho)e $s a &ery poerf') -

ray so'r(e.

Is)ote! 0)a(k ho)es (annot 0e o0ser&e!. 5e

ntres of *a)a/$es an! 0$nary stars are

fa&o'ra0)e )o(at$ons for !ete(t$on of 0)a(k ho)es.=A6AIES

The 'n$&erse $s f')) of *a)a/$es of !$fferent s$8es an! types. 4't the n$*ht sky

$s f$))e!$th stars 0e)on*$n* to a s$n*)e *a)a/y# o'r home m$)ky ay *a)a/y.

=a)a/$es are

(e)est$a) o0,e(ts ha&$n* 0$))$ons of stars as e)) as *as an! !'st he)! to*ether

$n spa(e 0y

*ra&$ty. O'r S'n an! a)) the stars $n the sky 0e)on* to m$)ky ay *a)a/y

h$(h appears asa ()o'!y 0an! of )$*ht a(ross the sky as tra$) of m$)k sp$))e! $n the sky. In

In!$an )$terat're$t $s (a))e! as Akash*an*a. M$)ky ay *a)a/y $s

a h$*h)y !$s( shape! *a)a/y. It (onta$ns

a0o't ;33 0$))$on stars )$ke o'r S'n. It $s so

h'*e that the )$*ht takes 133#333 years to

tra&e) from one e!*e to the other.

D'r$n* the 1H

th

an! ear)y 73th

(ent'ry the so)ar system as 0e)$e&e! to 0e at the (entre of

o'r *a)a/y. Th$s (on(ept as fo'n! to 0e ron

* $n 1H73s an! $t $s no esta0)$se! that the

so)ar system $s at a !$stan(e of a0o't 7:333

)$*ht years from the (entre. The S'n a)on*$th other mem0ers of the so)ar system m

o&es aro'n! *a)a(t$( (entre on(e $n a0o't 793m$))$on years. S$n(e the a*e of the S'n $s a0o't 9 0$))$on years $t fo))os that

the S'n

m$*ht ha&e ma!e at)east 73 re&o)'

t$ons a0o't the *a)a(t$( (entre.

There are a0o't three 0$))$on *a)a/$es )$ke

o'r m$)ky ay $n the o0ser&a0)e 'n$&erse.

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O0ser&a0)e 'n$&erse $s the part of the 'n$&ers

e a((ess$0)e to o'r 0est te)es(ope an! th$s

!$stan(e $s a0o't 13#333 m$))$on )$*ht years. As

a)rea!y ment$one! *a)a/$es appear $n

!$fferent shapes an! s$8es. In 1H7; E!$n <'00)e ()ass$f$e! *a)a/$es $nto three 0roa!

*ro'ps !epen!$n* on the$r str'('tre name)y

e))$pt$(a)# sp$ra) an! $rre*')ar. Most*a)a/$es that fa)) $nto these (ate*or$es are (a))e! Norma) *a)a/$es. These em$t

most)y star

)$*ht. O'r *a)a/y $s a sp$ra) *a)a/y.

Apart from the three ma,or types# some spe($a

) types of *a)a/$es ha&$n* a(t$&e *a)a(t$(

n'()e$ ha&e a)so 0een !$s(o&ere!. The (entra) re*$on of these *a)a/$es thros o't hot

*ases at )ar*e &e)o($ty of the or!er of 1333 kmJse(. Some *a)a/$es sho thee&$!en(e of

&$o)ent e/p)os$ons an! em$t &ery )ar*e amo'nt of

ener*y $n ra!$o# $nfrare!# or -ray a&e

)en*ths. These are (a))e! a(t$&e *a)a/$es.

Some other *a)a/$es e/h$0$t morpho)o*$(a)

feat'res s'(h as ta$)s# 0r$!*es# she))s#

arpsan! r$n*s. These feat'res are (a'se! 0y*ra&$tat$ona) en(o'nters 0eteen *a)a/$es.Re(ent)y the -ray sate))$te 5han!ra photo*

raphe! pa$rs of (o))$!$n* *a)a/$es $n

!$sr'pt$on an! mer*$n* pro(esses. It $s no 0e)$e&e! that e))$pt$(a) *a)a/$es

are mer*er

pro!'(ts of sp$ra) *a)a/$es. =a

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