After the Sun, which star has the greatest apparent brightness when viewed from Earth?

The correct answer is Sirius.

1. Understanding Apparent Brightness and Magnitude
Apparent brightness refers to how bright a celestial body appears to an observer on Earth. In astronomy, this is measured using the apparent magnitude scale (represented by m).
On this scale, lower or more negative numbers correspond to brighter objects, while higher positive numbers correspond to dimmer objects.

2. Comparing the Given Stars
The Sun dominates our sky with an apparent magnitude of approximately:

$m=-26.74$

Among all other stars in the night sky, we compare the apparent magnitudes of the options provided:
• Sirius: Apparent magnitude of approximately $m=-1.46$
• Arcturus: Apparent magnitude of approximately $m=-0.05$
• Rigel: Apparent magnitude of approximately $m=+0.13$
• Antares: Apparent magnitude ranging from approximately $m=+0.6$ to $m=+0.9$

3. Conclusion
With an apparent magnitude of $m=-1.46$, Sirius (also known as the "Dog Star" or Alpha Canis Majoris) has the most negative value, making it the brightest star visible in Earth's sky after the Sun.