Solar Observations in Bulgaria

 

The Sun is a star of a yellow dwarf type with spectral class of G2V. G2 means that it has a surface temperature of approximately 5,770 K (≈5,500 °C) giving it a white color that often, because of atmospheric scattering, appears yellow when seen from the surface of the Earth. V means that it belongs to the stellar population of the main sequence in the “color-magnitude“stellar diagram.

The Sun orbits the center of the Milky Way galaxy at a distance of approximately 30 000 light years from the galactic center, moving generally in the direction of Cygnus constellation and completing one revolution in about 250 million years (one Galactic year). Its orbital speed was thought to be 220±20 km/s, but a new estimation gives about 250 km/s. Except that basic motion, the Sun moves with a speed of 20 km/s in a direction to the Hercules constellation, according to the relatively close stars (up to 200 parsecs).

 

 

 

Spectral type:                  G2V

Visual magnitude:          -26.74

Absolute magnitude:     +4.83

 

 

Surface area:                            609 x 10¹⁶ m²

Mass (M_☉):                              1.989 x 10³⁰ kg (332 946 masses of Earth)

Mean density:                           1.409 g/cm³ (0.256 of mean density of Earth)

Central density:                        ≈98 g/cm³

Luminosity:                               3.86 x 10³³ erg/s  (3.86 x 10²⁶ W)

Angular velocity of rotation (at latitude 16º):               2.865 x 10^-6 rad/s

Linear velocity of rotation for the point at equator:    2.025 km/s

Acceleration at the solar surface (photosphere):     274 m/s² (28 gÅ)

 

 

Mean (1 astronomical unit-AU):        149.6 x 10⁶ km (measured by telemetry method on 2009 1AU* = 149 597 870 700m; 215.1R_☉)

In perihelium:                                       147.1 x 10⁶ km (147 098 074 km or 0.9832898912 AU)

In aphelium:                                         152.1 x 10⁶ km (152 097 701 km or 1.0167103335 AU)

 

Apparent radius at 1 AU:                                                                             959.63”

Apparent radius plus irradiation (for the disc edge observation):      961.2”

Flatness (difference between equatorial and polar radius):               0.05”?

 

At 1 AU:             31’ 59.26”

In perihelion:   32’ 31.89”

In aphelion:      31’ 27.70”

 

Sidereal rotation:          25.38 days or 14,184 degree/day

Sinodic rotation:           27.28 days or 13,199 degree/day (Carrington rotation)

 

Inclination of Sun’s equator plane to the ecliptic plane: 7° 15’

 

1’ of arc at 1 AU:        43 520 km

1” of arc at 1 AU:             725.3 km

 

 

Sun Basic Facts
Age	At least 4.5 x 109 years in present state
Chemical composition of photosphere ( by mass, in %)
Hydrogen	73.46
Helium	24.85
Oxygen	0.77
Carbon	0.29
Iron	0.16
Neon	0.12
Nitrogen	0.09
Silicon	0.07
Magnesium	0.05
Sulfur	0.04
Other	0.10
Density (water=1000):
Mean density of entire Sun	1410 kg/m3
Interior (center of Sun)	160000 kg/m3
Surface (photosphere)	10–6 kg/m3
Chromosphere	10–9 kg/m3
Low corona	10–13 kg/m3
Sea level atmosphere of Earth (for comparison)	1.2 kg/m3
Diameter (at the Photosphere)	1.39x106 km (109 times the diameter of Earth and 9.75 times the diameter of Jupiter
Distance
mean distance from Earth	149 597 870 700m (~149.6 x106 km = 1 AU)
Variation in distance through the year	±1.5 percent
Magnetic field strengths for typical features:
Sunspots	0.3 tesla                    (3000 Gauss)
Polar field	10–4 tesla                 (1÷2 Gauss)
Bright, chromospheric network	0.0025 tesla             (25 Gauss)
Ephemeris (unipolar) active regions	0.0020 tesla             (20 Gauss)
Chromospheric plages	0.02 tesla                  (200 Gauss)
Prominences	10–3 to 10–2 tesla   (10÷100 Gauss)
Earth (for comparison)	30÷60x10–6 tesla    (0.3÷0.6 Gauss)
Mass	1.99x1030 kg (or 333 000 times the mass of Earth)
Differential rotation (as seen from Earth):
Of solar equator	26.8 days
At solar latitude 30o	28.2 days
At solar latitude 60o	30.8 days
At solar latitude 75o	31.8 days
Solar radiation:
Entire Sun	3.83x1023 kW
Unit area of surface of Sun	6.29x104 kW/m2
Received at top of Earth’s atmosphere   Received at the Earth’s surface (for Bulgaria)	1366 W/m2 (from 1,412 W/m2 in early January to 1,321 W/m2 in early July)  ≈175 W/m2
Surface brightness of the Sun (photosphere):
Compared to full Moon	398 000 times
Compared to inner corona	300 000 times
Compared to outer corona	1010 times
Compared to daytime sky on Pikes Peak	100 000 times
Compared to daytime sky at Orange, N.J.	1000 times
Temperature:
Interior (center)	15 000 000 K
Surface (photosphere)	6050 K
Sunspot umbra (typical)	4240 K
Penumbra (typical)	5680 K
Chromosphere	4300 to 50 000 K
Corona	800 000 to 3 000 000 K
Volume	1.41x1027 m3 (or 1.3 million times the volume of Earth)

 

1AU* The International System of Units (SI)