<P> As viewed from Earth, the visible region of the Milky Way's Galactic plane occupies an area of the sky that includes 30 constellations . The center of the Galaxy lies in the direction of the constellation Sagittarius; it is here that the Milky Way is brightest . From Sagittarius, the hazy band of white light appears to pass around to the Galactic anticenter in Auriga . The band then continues the rest of the way around the sky, back to Sagittarius . The band divides the night sky into two roughly equal hemispheres . </P> <P> The Galactic plane is inclined by about 60 degrees to the ecliptic (the plane of Earth's orbit). Relative to the celestial equator, it passes as far north as the constellation of Cassiopeia and as far south as the constellation of Crux, indicating the high inclination of Earth's equatorial plane and the plane of the ecliptic, relative to the Galactic plane . The north Galactic pole is situated at right ascension 12 49, declination + 27.4 ° (B1950) near β Comae Berenices, and the south Galactic pole is near α Sculptoris . Because of this high inclination, depending on the time of night and year, the arc of the Milky Way may appear relatively low or relatively high in the sky . For observers from approximately 65 degrees north to 65 degrees south on Earth's surface, the Milky Way passes directly overhead twice a day . </P> <P> The Milky Way is the second - largest galaxy in the Local Group, with its stellar disk approximately 100,000 ly (30 kpc) in diameter, and, on average, approximately 1,000 ly (0.3 kpc) thick . As a guide to the relative physical scale of the Milky Way, if the Solar System out to Neptune were the size of a US quarter (24.3 mm (0.955 in)), the Milky Way would be approximately the size of the continental United States . A ring - like filament of stars wrapping around the Milky Way may belong to the Milky Way itself, rippling above and below the relatively flat galactic plane . If so, that would mean a diameter of 150,000--180,000 light - years (46--55 kpc). </P> <P> Estimates of the mass of the Milky Way vary, depending upon the method and data used . At the low end of the estimate range, the mass of the Milky Way is 5.8 × 10 solar masses (M), somewhat less than that of the Andromeda Galaxy . Measurements using the Very Long Baseline Array in 2009 found velocities as large as 254 km / s (570,000 mph) for stars at the outer edge of the Milky Way . Because the orbital velocity depends on the total mass inside the orbital radius, this suggests that the Milky Way is more massive, roughly equaling the mass of Andromeda Galaxy at 7 × 10 M within 160,000 ly (49 kpc) of its center . In 2010, a measurement of the radial velocity of halo stars found that the mass enclosed within 80 kilo parsecs is 7 × 10 M . According to a study published in 2014, the mass of the entire Milky Way is estimated to be 8.5 × 10 M, which is about half the mass of the Andromeda Galaxy . </P>

What is the thickness of the milky way