Distance
Determining a precise distance to the LMC, as with any other galaxy, was challenging due to the use of standard candles for calculating distances, with the primary problem being that many of the standard candles are not as 'standard' as one would like; in many cases, the age and/or metallicity of the standard candle plays a role in determining the intrinsic luminosity of the object. The distance to the LMC has been calculated using a variety of standard candles, with Cepheid variables being one of the most popular. Cepheids have been shown to have a relationship between their absolute luminosity and the period over which their brightness varies. However, Cepheids appear to suffer from a metallicity effect, where Cepheids of different metallicities have different period–luminosity relations. Unfortunately, the Cepheids in the Milky Way typically used to calibrate the period–luminosity relation are more metal rich than those found in the LMC.
In the era of 8-meter-class telescopes, eclipsing binaries have been found throughout the Local Group. Parameters of these systems can be measured without mass or compositional assumptions. The light echoes of supernova 1987A are also geometric measurements, without any stellar models or assumptions.
Recently, the Cepheid absolute luminosity has been re-calibrated using Cepheid variables in the galaxy NGC 4258 that cover a range of metallicities. Using this improved calibration, they find an absolute distance modulus of 18.41, or 48 kpc (~157,000 light years). This distance, which is slightly shorter than the typically assumed distance of 50 kpc, has been confirmed by other authors.
By cross-correlating different measurement methods, one can bound the distance; the residual errors are now less than the estimated size parameters of the LMC. Further work involves measuring the position of a target star or star system within the galaxy (i.e., toward or away from the observer).
Read more about this topic: Large Magellanic Cloud
Famous quotes containing the word distance:
“The rage for road building is beneficent for America, where vast distance is so main a consideration in our domestic politics and trade, inasmuch as the great political promise of the invention is to hold the Union staunch, whose days already seem numbered by the mere inconvenience of transporting representatives, judges and officers across such tedious distances of land and water.”
—Ralph Waldo Emerson (1803–1882)
“I do believe that the outward and the inward life correspond; that if any should succeed to live a higher life, others would not know of it; that difference and distance are one. To set about living a true life is to go on a journey to a distant country, gradually to find ourselves surrounded by new scenes and men; and as long as the old are around me, I know that I am not in any true sense living a new or a better life.”
—Henry David Thoreau (1817–1862)
“Remember? We sat on a slab of rock.
From this distance in time,
it seems the color
of iris, rotting and turning purpler,
but it was only
the usual gray rock”
—Robert Lowell (1917–1977)