Question

When we look at stars, we notice that some appear brighter than others. Is Sirius really brighter than Rigel, or is Sirius much closer to Earth, giving it the appearance of being brighter? Actually, Sirius is about one hundred times closer to Earth than Rigel. If the two stars were the same distance from Earth, Rigel would appear much brighter. We use two terms to reference the brightness of a star: absolute magnitude and apparent magnitude. Absolute magnitude is the measure of the light given off by a star, while apparent magnitude refers to the amount of light received on Earth. The color of a star indicates its temperature. Blue-white stars are very hot, while orange-red stars are relatively cool. The phrase 'absolute magnitude' refers to the amount of light given off by a star.

Answer 1

Sirius has an apparent magnitude of -1.5, which makes it appear very bright in the sky, but this perceived brightness is also due to its much closer proximity to Earth compared to other stars. The magnitude scale works inversely, with higher numbers indicating fainter stars, and Sirius B, being much fainter than Sirius A, is not visible to the eye.

Step-by-step explanation:

The apparent magnitude of a star is a measure of how bright it appears from Earth, whereas the absolute magnitude refers to how bright the star would be at a standard distance of 10 parsecs. Sirius, the brightest star in the sky, has an apparent magnitude of -1.5, which is brighter than average for a first-magnitude star. The brightness of Sirius compared to another star like Rigel can be misleading because Sirius is about 100 times closer to Earth than Rigel is. If Rigel were at the same distance as Sirius, it would appear much brighter than Sirius. The magnitude scale is inverse, meaning that a higher magnitude number corresponds to a fainter star. As an example, Sirius A's dim companion, Sirius B, is 10,000 times less bright than Sirius A. Given the description of light intensity differences and the magnitude scale, the apparent magnitude of Sirius B cannot be calculated precisely without additional data or a reference chart. Typically, the threshold for visibility to the eye is an apparent magnitude of around 6 or 7; therefore, Sirius B, being significantly dimmer than Sirius A, is not visible.