Determination of distances to space objects – To determine the distances to the most distant objects in the universe, this method has been developed. Based on the results of research in the field of redshifts in the electromagnetic radiation spectra of relatively close galactic objects, the distances to which were measured by other methods, Hubble’s law was formulated. As a result, it became possible to determine the distance to an object by the value of the redshift in its spectrum.
This method allows us to study the distribution of gas clouds in the intergalactic medium.
Absorption bands can be seen in the spectrum of electromagnetic radiation that comes to us from distant galactic sources, such as quasars. This happens in the case of electromagnetic radiation passing through intergalactic gas clouds. These clouds are located at different distances from the observer looking at it with the help of his vision. According to Hubble’s law, the absorption lines characteristic of a certain gas contained in clouds have different redshifts. Due to the displacement of each of the lines, it is possible to determine the distance to specific clouds, and due to the width of the spectral lines, the power of these clouds by the observer’s line of sight.
These intergalactic gas clouds are mainly composed of hydrogen. The effect, dubbed “Lyman alpha forest”, was first discovered by observing one of the most intense spectral lines of hydrogen, called “lyman alpha”, which is the strongest. During observations of distant radiation sources, it was found that this spectral absorption line is present at many wave frequencies. At the same time, it is registered as a series – “forest” of continuous absorption lines in the spectrum, which are separated by sections of the spectrum in which hydrogen is absent. This fact suggests that there are hydrogen-free zones between clouds located at a distance from the observer’s eyes. The “forest” of discrete spectral absorption lines of intergalactic gas clouds, which may be not only hydrogen, but also others, may look different when observed from different angles. It is also possible to obtain a volumetric picture of the distribution of gas clouds in space.
In the meaning of parallax, or “parallel” (from the Greek parallaxis – parallax).
This is the oldest way to determine the distance to inaccessible or distant objects. Parallax is also meant.
This method was first used to determine the distances from the Earth to the Moon and the Sun. In addition, the maximum possible distances on Earth were used as a base – those that are comparable to the size of our planet. Subsequently, the distances to the Moon and the Sun were repeatedly clarified using radar methods.
The method that is used today was used for the first measurements of distances to stars. In these situations, segments comparable to the value of an astronomical unit were used for the base.
The most optimal distance to which this method can still be applied is 100 parsecs, since the angular size of the ellipse, which is described by a star located at this distance, is 0.01 arcseconds. This angle can be measured with existing instruments using minimal angles.
Based on radar data
Radar is a modern and fairly accurate way to measure distances from the Earth to the bodies of the Solar system. The data on the distance between the Earth and the Sun were clarified using radar. It turned out to be equal to 149597867.9 km or 0.9 km.
The adoption of Kepler’s “third Law”
If the time of the planet’s revolution around the Sun is known and its mass does not matter in comparison with the mass of the Sun, it is possible to calculate the major semi-axis of its orbit using Kepler’s third law. Then, using the ratios of astrometry and celestial mechanics, it is easy to determine the distance from Earth to a given planet at any given time.
Application of the photometric method
Thanks to studies of nearby stars, the distances to which were measured by parallax, it was possible to detect the dependence of their absolute stellar magnitudes on the spectral or any other characteristics of these stars. Using a photometer to measure the magnitude of a star, you can find out the absolute magnitude of a star and determine the distance to it, since the luminous flux is inversely proportional to the square of the distance to the light source.
In recent years, the method of determining the distance to distant objects, such as galaxies and their clusters, using visual stellar magnitudes of supernovae of a certain type has become widely used. These new supernovae are distinguished by the presence of distinctive details in the spectra, as well as features of the brightness curves during flashes and are easily recognizable, whereas their luminosities at maximum brightness differ very little from each other.
The photovoltaic measurement method is also used to determine the distance to galaxies by measuring their surface brightness, which is more or less standard in certain types of such star systems.
The level of accuracy of determining the distance to the cepheids is a photometric method. At the same time, it stands out because its application has proven to be very effective in determining distances to star clusters and galaxies. It turned out that the luminosities, or, as they are also called, the absolute stellar magnitudes of these variable stars, are directly dependent on the period of change in their brightness. Cepheids were found in the systems of our galaxy and in the nearest galactic systems, thanks to this it was possible to determine the distance to these objects.
