Here's why the statement is incorrect:
* Declination: Declination is a celestial coordinate that measures a star's angular distance north or south of the celestial equator. It's similar to latitude on Earth.
* Negative Declination: Negative declination simply means the star is located south of the celestial equator.
* Observing From the Northern Hemisphere: You can observe stars with negative declination from the Northern Hemisphere depending on your location.
Why You Might Have Heard That:
The confusion might arise from the idea that certain stars with negative declination may be below the horizon at certain times of the year, depending on the observer's latitude.
For example, a star with a declination of -60 degrees would never be visible from the North Pole (latitude 90 degrees North), as it would always be below the horizon. However, someone at a lower latitude, like 40 degrees North, could see that same star during certain times of the year when it's above their horizon.
In summary:
You can absolutely see stars with negative declination from the Northern Hemisphere, but the visibility depends on your latitude and the time of year.
