Answer:
A. Canopus
Step-by-step explanation:
Canopus is a first-magnitude star in the constellation Carina: the second brightest star in the heavens.
Which star is brighter, Sirius or Canopus, and why?
From Earth Sirius appears to be about twice as bright as Canopus. However, Sirius is only 8.6 lightyears from us, but Canopus is 310 lightyears away. Since light dims by the square of the distance we can say that if they were of equal apparent brightness Canopus would be (310/8.6)^2 or 1,300 time brighter.
In actuality, Sirius is 25.4 times as luminous as the sun, while Canopus is 10,700 times more luminous. So Canopus is 421 times brighter than Sirius. If you are asking why the brighter one looks dimmer, I have answered that.
If you are asking why Canopus is actually so much brighter than Sirius, I will try to answer that now. Stars are powered by atomic reactions that go on in or near the core. These reactions are caused by extreme heat and pressure. These are caused by the weight of the star crushing down from above. The larger the star the greater the heat and pressure, the faster the star burns its fuel, and the brighter it is. Sirius is just a bit over twice the mass of the sun (2.063), but Canopus is between 8 and 10 times as hefty as the sun.
Stars use the heat and pressure in the core to turn hydrogen into helium, which results in light. When it runs out of hydrogen the star starts to collapse. That generates more pressure and heat and allows the star to turn helium into carbon. This makes the star swell up and its surface temperature cools. The larger the star is cooler, but it has many times the surface area to generate light. Canopus is now burning helium and has swollen, but its surface temperature is still 3/4 that of Sirius. Sirius is only 1.7 times the width of the sun, but Canopus is 71 times bigger or 1,750 times the surface area.
If you did not catch all of that, I’ll sum it up. Canopus is more massive, and has a MUCH bigger size than Sirius. This allows it to produce a lot of light on its MUCH larger surface area and to radiate it out into space.