## Tag Archive

amateur astronomy awk bash b[e] supergiant cartoon conference convert evolved star exoplanet fedora figaro fits fun galaxy iraf large magellanic cloud latex linux lmc machine learning magellanic clouds massive star matplotlib meteor mypaper paper peblo photometry planet pro-am pyraf python red supergiant scisoft skinakas observatory small magellanic cloud smc spectroscopy starlink talk ubuntu university of crete video x-ray yellow hypergiant

## Sexagesimal and radian to degree conversion

A. If you want to convert sexagesimal numbers (RA=hh:mm:ss.s Dec=±dd:mm:ss) to degrees then use these relations:

RA>deg: 15 x (hh + mm/60 + ss.s/3600)
Dec>deg: ±dd ± (mm/60 + ss/3600)

These relations are pretty easy to remember since
> 1 hour the sky rotates 15 degrees (360degrees in 24 hours)
> 1 minute = 60 seconds
> 1 hour = 60 minutes = 60 seconds
> Caution with Dec: when Dec is positive you add the rest while when it is negative you subtract.

B. For radians to degrees conversion use the relation:

## Useful astronomical numbers

Just some useful numbers and units to remember and to have an easy access to!
[last updated: 29 Dec 2011]

>> Distance

1 AU = 150 x 106 km

1 pc = 3.09 × 1013 km = 206260 AU = 3.26 ly

1 ly = 9.4 x 1012 km = 64 x 103 = 0.31 pc

>> Sun

L = 3.86 x 1026 W = 3.86 x 1033 erg / s

MV,☉ = Mbol,☉ = 4.8

M = 2 x 1030 kg

R = 6.96 x 105 km

V☉,relative = 30 km/s

T = 5780 K

RSun-GC = 8 kpc

tgalactic orbit = 250 x 106 yr

Vgalactic rotation = 200 km/s

solar wind’s energy ~ 10-7 L (on average)

solar wind’s density (in the vicinity of Earth) ~ 5 particles / cm3

solar wind’s velocity (in the vicinity of Earth) ~ 400 km / s

mass loss ~ 10-14 M / yr

>> Earth

MEarth = 5.974 x 1024 kg

REarth = 6371 km

ρEarth = 5.5 g/cm3

>> Milky Way / Galaxy

haloradius > 75 kpc (perhaps 100 kpc)

dust ± 300 pc from disk level

stars ± 1000 pc from disk level

MMW = -20.5 ( 25 mag more than MSun, 1010 times that of Sun)

>> Ionization potential

for H = 13.6 eV

for He = 24.6 eV (one electron) + 54.4 eV (both electrons)

>> Hydrogen atom

R = 1 Å

>> Extinction

Sun’s neighbourhood: ~ 1 mag/kpc

towards GC: ~ 21 mag/kpc – 1 optical photon per 1012 reaches us, while 1 out of 10 in IR

>> magnitude difference: 5 mags = 100 times in flux [m1-m2=-2.5 log10(f1/f2)]