The Sun is a yellow dwarf star (G2V), about 4.6 billion years old, and the dominant gravitational force in the Solar System. It has a diameter of roughly 1.4 million kilometers and contains around 99.8% of the Solar System’s mass. Nuclear fusion in its core converts hydrogen into helium, producing energy that warms the planets. Above the core lie the radiative and convective zones, followed by the visible photosphere (~5,500 °C), the chromosphere, and the much hotter corona (~2 million °C).
Source: science.nasa.gov
19/02/2019
It isn't every night that a comet passes a galaxy. Last Thursday, though, binocular comet C/2018 Y1 (Iwamoto) moved nearly in front of a spiral galaxy of approximately the same brightness: NGC 2903. Comet Iwamoto was discovered late last year and orbits the Sun in a long ellipse. It last visited the inner Solar System during the Middle Ages, around the year 648. The comet reached its closest point to the Sun -- between Earth and Mars -- on February 6, and its closest point to Earth a few days ago, on February 13. The featured time-lapse video condenses almost three hours into about ten seconds, and was captured last week from Switzerland. At that time Comet Iwamoto, sporting a green coma, was about 10 light minutes distant, while spiral galaxy NGC 2903 remained about 30 million light years away. Two satellites zip diagonally through the field about a third of the way through the video. Typically, a few comets each year become as bright as Comet Iwamoto.