Nameģ0 as seen with the European Extremely Large Telescope (E-ELT) or Hubble Space Telescope
It is also important to note that the magnitude system is only meaningful when magnitudes are compared when measured through the same wavelength band. More accurate measurements put its apparent magnitude at 0.03. As a useful reference point, the star, Vega is taken to be of 0 magnitude. The dimmest object currently observable with the largest telescopes have a magnitude of 30. At the other end of the scale, as the light gathering power of telescopes has increased, the magnitude scale has extended to encompass much fainter stars. The Sun has an apparent magnitude of -26.74, while Sirius has a magnitude of -1.46. These bright starts are accommodated by allowing negative magnitudes. To make things more confusing, the brightest stars in the sky exceed magnitude 1. In calculations, however, the factor 2.5 is often used. The fifth root of 100 (since magnitude 6 stars must be 1: x 5 is known as Pogson's Ratio. Thus, a first magnitude star is about 2.512 times as bright as a second magnitude star.
In 1856, Norman Robert Pogson formalized the system by defining a typical first magnitude star as a star that is 100 times as bright as a typical sixth magnitude star. Improvements in the light gathering power of telescopes made it possible to compare the intensities of the light from stars more accurately. The Hipparchus scale went from magnitude 1, for the brightest stars, up to magnitude 6, for those stars which were barely visible. Magnitude of Stars Apparent MagnitudeĮarly Greek astronomers used a scale of magnitude devised by Hipparchus around the 2nd century BC, which was based on how bright stars appeared with the naked eye. If the star is not further than 500 light-years, then the parallax shift of the star can be used to find the distance from the Earth.ĭistance (in parsecs) = 1/parallex angle.
UNIT LARGER THAN LIGHT YEARS PC
also used are kpc =1000 pc and Mpc =1 million pc The parsec in trigonometric terms.ġ Parsec = 3.08568025 × 10 16 m. The two dimensions that specify this triangle are the parallax angle (defined as 1 arcsecond) and the opposite side (defined as 1 Astronomical Unit (AU), the distance from the Earth to the Sun).įigure 2. The parsec is defined to be the distance at which a star would have a parallax angle p equal to one second of arc (1/3600 deg). The other commonly used unit in astronomy and in Star Trek is called the Parsec (parallax of one arc second). The edge of the observable universe is 46.5 Giga light years away. The andromeda galaxy is 2.3 million light-years away. The Milky Way Galaxy is about 150,000 light-years across The distance from the Earth to the nearest star (Alpha Centauri A or B) after our Sun is 4.3 ly. With our new measuring sticks to hand we can give a few examples of the scale of the universe. All electromagnetic waves travel at a speed of x 299,792,458 ms -1 in a vacuum and with an average year being 365.25 days, one light year is 299,792,458 x 10 8ms -1 x (365.25 x 24 x 60 x 60) s =ĩ.46073 x 10 15 m. The light-year, as its name would suggest, is the distance travelled by light in one year. Moving to larger distances even the AU becomes unweildly and so the next suitable unit is the light-year. 1 Astronomical Unit = 149 598 000 km Light Year One natural and practical unit we can devise is the distance from the Sun to the Earth. We must introduce new length scales with which can span the heavens. The distances involved in the universe are so vast that metres or kilometers will just not suffice. I mean, you may think it's a long way down the road to the chemist's, but that's just peanuts to space. You just won't believe how vastly, hugely, mind-bogglingly big it is. In the words of Douglas Adams, the author of The Hitch-Hiker's Guide to the Galaxy: Space is big.