by Madhurani Chavan | फेब्रुवारी 25, 2022 | English, खगोलशास्त्र, मधुरानी
VY Canis Majoris or VY CMa is a red hypergiant star. It is located in the constellation Canis Major. It is one of the largest and brightest red hypergiants observed so far. It has a diameter of 1800 solar radii. This star emits energy very quickly and therefore, only exists for a few million years. It is estimated to be 4900 light-years away from Earth. This star shows periodic light changes that last for approximately 2200 days.
The crimson star
The first known recorded observation of VY Canis Majoris is in the star catalog of Jérôme Lalande, who recorded it on 7th March 1801. Since 1847, VY CMa has been known to be a crimson star. Originally, University of Minnesota Professor Roberta M. Humphreys approximated that the radius of VY CMa is 1800-2100 times that of the Sun. This would make it the largest known star based on its radius.
A big star
There have been conflicting opinions of the properties of VY CMa. A commonly held theory states that the star is a very large and luminous red hypergiant. However, various larger estimates of the size and luminosity fall outside the bounds of current stellar theory. In another theory, the star is a normal red supergiant with a radius around 600 times that of our Sun.
The surface of VY CMa
This star also illustrates the conceptual problem of defining the “surface” of very large stars. This is very important for multiple reasons, including determining its radius and thus its size. It is a hundred thousand times less dense than the atmosphere of Earth (air) at sea level. Its average density is 0.000005 to 0.000010 kg per metre³. Additionally, the star is constantly losing mass at an astounding rate. The boundary of such a star is usually defined by its “Roseland Radius”, which is based on its opaqueness to light.
Compiled by: Madhurani Chavan
by Madhurani Chavan | फेब्रुवारी 25, 2022 | खगोलशास्त्र, मधुरानी
Sirius is the brightest star system in Earth’s night sky. The name “Seirios”, means “glowing” or “scorcher”. What appears to be a single star to the naked eye is actually a binary system of the white dwarf. This system is formally known as Alpha Canis Majoris or alpha CMa.
Sirius in ancient Egypt
Sirius is recorded in the earliest astronomical records. It was known in ancient Egypt as “Sopdet”, which is written in Greek as “Sothis”. The Egyptians based their calendar on the heliacal rising of Sirius. This heliacal rising marked the flooding of the Nile in ancient Egypt and the “dog days” of summer for the ancient Greeks.
Sirius to Polynesians
To the Polynesians in the southern hemisphere, it marked winter. The heliacal rising of Sirius refers to the day it becomes visible just before sunrise after moving far away from the glare of the Sun.
Dogstar
Due to its prominent position in Canis Majoris (greater Dog) constellation, Sirius is often also referred to as the “Dogstar”.
Brightness
Sirius is the brightest star system in the night sky with almost twice the brightness of the second brightest star, Canopus. However, it is not as bright as the moon, Venus, or Jupiter. In fact, even Mars and Mercury appear brighter than Sirius at times.
Types of Sirius
The two stars of the Sirius system are termed Sirius A is a white main-sequence star with an estimated surface temperature of 9,940 K. It has an estimated mass that is twice that of the Sun. Sirius B is a star that has already evolved off the main sequence and transformed into a white dwarf. It has a mass almost equal to that of the Sun. It is one of the most massive white dwarfs known to us.
Red, blue, or white?
Greek astronomer Ptolemy had described the star of Sirius to be red in color around 1 CE and ancient China has been describing it as white since 4 CE. Astronomers believe that this star keeps changing its color. However, the reason is still being debated.
Compiled by: Madhurani Chavan
by Madhurani Chavan | फेब्रुवारी 25, 2022 | English, खगोलशास्त्र, मधुरानी
Outer space is a void that lies beyond the uppermost ranges of the atmosphere of Earth and between all other objects in the universe. Although it is considered to be a void, outer space can be thought of as an environment in itself. Radiation and objects pass freely through it. A human or another living being in the outer space environment without any protection would not survive even for a few moments.
Total vacuum
The basic environmental characteristic of outer space is the vacuum for the nearly total absence of gas molecules. The gravitational attraction of large bodies, such as planets and stars, pulls the gas molecules close to their surfaces, which leaves the space between them practically empty. Stray gas molecules are usually found between these bodies. Their density is so low that they can be thought of as being unreal.
Effect of pressure in outer space
On Earth, the atmosphere applies pressure in all directions. At sea level, it is 101 kilopascals but in space, it is almost zero. With no external pressure, the air within a human’s lungs, without any kind of protective shield, would immediately rush out into the vacuum.
Effect of pressure in space on humans
The sudden absence of external pressure that balances the internal pressure of the body would damage delicate tissues such as the eardrums and the capillaries. The body would swell, causing tissue damage and a lack of oxygen supply to the brain. This would result in unconsciousness in under 10 seconds. Dissolved gases in the body fluids would expand, causing the skin to stretch much like a pumped balloon. Bubbles would form in the bloodstream making it ineffective as transport of oxygen and nutrients to the body’s cells.
Temperature in space
The temperature in outer space is hazardous. The objects that receive sunlight in space and are at Earth’s distance from the Sun, can scale to over 120 °C while those on the shaded side can be as low as – 100 °C. Because of the space environment, a comfortable temperature range cannot be sustained, posing grave problems.
Other environmental factors
There are other environmental factors in space such as microgravity, radiation of the electrically charged particles from the Sun, ultraviolet radiation and meteoroids. Meteoroids are small bits of rock and metal leftover from the formation of the solar system about trillions of years ago and from comets and asteroids collisions. They are small but travel at very high velocities and can easily seep into the human skin. Debris from previous space missions is also very dangerous. A tiny paint chip traveling at thousands of kilometers per hour can do significant damage.
Compiled by Madhurani Chavan
