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, मधुरानी
Arcturus is the brightest star in the northern celestial hemisphere. It lies in the constellation “Bootes” and is known as “Alpha Bootes”. It is the fourth brightest star in the night sky, after Sirius, Canopus and Alpha Centauri. It lies barely 36.7 light-years from Earth, making it very close by celestial standards.
Early observations
Arcturus has been significant to observers since recorded antiquity. It was linked to the God Enlil and is also known as “Shudun”, meaning yoke, in ancient Mesopotamia. Ptolemy of ancient Greece described Arcturus as “subrufa” or slightly red. Prehistoric Polynesian navigators knew Arcturus as “Hōkūle’a”, the star of joy. This civilization used Arcturus as a navigational guide. The use of Arcturus is one of the methods by which Polynesians became such fabled sailors without any instruments.
Visibility
Arcturus can be observed during the day with a telescope. French mathematician and astronomer Jean-Baptiste Morin did this in 1635, making it the first star to be seen during the day. Arcturus is a type KO III red giant star. Visibly, it is at least 110 times brighter than Sun. However, most of the light given off by it is infrared and not visible to the naked eye. This is because the surface is cooler than the Sun.
Binary system
It is suggested that Arcturus is actually a part of a binary star system. The secondary star seems to be about 20 times dimmer than the primary one and orbits so close to Arcturus that it is not possible as of yet to distinguish it from the main star. There have been many focussed observations undertaken for this but the results remain inconclusive.
Arcturus became famous when its light was rumored to be the mechanism used to open the 1933 Chicago World’s Fair. The star was chosen as it was thought that light from Arcturus has started its journey at about the time of the previous Chicago World’s Fair in 1893. The star is 36.7 light-years from Earth and the light started its journey in 1896.
Compiled by: Madhurani Chavan
by Madhurani Chavan | फेब्रुवारी 25, 2022 | English, मधुरानी
Betelgeuse is the ninth brightest star in the night sky and the second brightest in the constellation of Orion. It is also known by its official name or Bayer designation “alpha Orionis”. This is often shortened to alpha-Orionis or alpha ori. The star’s name is derived from the Arabic Yad al-Jauzā, which means “the hand of Orion”. It refers to the star’s position in the Orion constellation.
Classification
The star is classified as a red supergiant. It is one of the largest and most luminous observable stars. If Betelgeuse were in the solar system in place of the Sun, its surface would extend past the asteroid belt. It would possibly extend to the orbit of Jupiter and beyond. The resulting mass would be completely engulfing Mercury, Venus, Earth and Mars. Betelgeuse has a mass estimated to be around 30 times that of the Sun.
Variable brightness
It is one of the stars with greatly varying brightness. Sir John Herschel, in Outlines of Astronomy, first described the variation in Betelgeuse’s brightness in 1836. This makes it easy to spot and identify with the naked eye. It also has a distinctive reddish-orange color.
Eventual fate
Its fate depends on its mass. This is a critical factor that is not well understood. The most likely scenario is that the supergiant will continue to burn and fuse elements until its core is iron, at which point Betelgeuse will explode as a type II supernova. As of 2014, the most recent theory suggests that it will explode as a supernova within 1,00,000 years. The event is expected to leave a neutron star 20 km in diameter.
Compiled by: Madhurani Chavan
by Madhurani Chavan | फेब्रुवारी 25, 2022 | English, मधुरानी
Polaris is the brightest star in the constellation Ursa Minor and the 45th brightest star in the night sky. It is very close to the north celestial pole and is commonly used for navigation. Thus, it is also commonly known as the pole star, loadestar, or guiding star.
Star system of Polaris
It is actually a multiple-star system. It consists of one main star, Alpha Ursa Minoris (UMi) Aa and two smaller companions, Alpha UMi AB. There are also two distant components, Alpha UMi C and Alpha UMi D.
Classification and characteristics
Alpha UMi Aa is a yellow supergiant with a mass 4.5 times that of the Sun. The two smaller companions are as follows:
•Alpha UMi B – is a main-sequence star orbiting at a distance of 2400 AU and a mass 1.39 times that of the Sun.
• Alpha UMi Ab – is a very close main-sequence star at a distance of 18.8 AU and a mass 1.26 times that of the Sun.
Alpha UMi Aa is visible to the naked eye and even a modest telescope can see Alpha UMi B. The system is at an approximate distance of 434 light-years from Earth.
Pole star
Because Alpha UMi nearly lies in a direct line with the axis of Earth’s rotation “above” the North Pole, it stands almost motionless in the sky. As a result, all the stars of the Northern sky appear to rotate around Polaris. It makes an excellent fixed point to draw measurements for celestial navigation and astrometry.
The celestial North Pole is not fixed. It moves due to Earth’s motion. As a result, Polaris wants always a pole star and will not be one after a few centuries.
Compiled by: Madhurani Chavan
by Madhurani Chavan | फेब्रुवारी 25, 2022 | English, मधुरानी
Space begins where Earth’s atmosphere ends. There was a time when space was believed to be completely empty. However, this is not true. The vast gaps between the stars and the planets are filled with huge amounts of gases and dust. Even the emptiest parts of space contain at least a few hundred atoms or molecules per cubic meter.
• Space is black
There is neither air to breathe nor light to scatter in space, making it difficult for humans to survive. Space is black and not blue like a sky. This is because the number of oxygen molecules is comparatively less in space. It mainly consists of a vacuum and the molecules present are not sufficiently close because of which sound does not get transmitted.
• How big is it?
No one really knows how big space is. Long distances in space are measured in “light-year”, which represents the distance that light takes to travel in a year. This is roughly about 9.3 trillion km.
• Marvels of space
Besides vacuum, space consists of planets, stars, several hundred galaxies, matter, dust, gases and so on. Just like we have winds, there are solar winds that occur in space. Let us look at all the amazing things that exist high up in the heavens that leave us awestruck every time we explore them.
