How come you can see certain constellations in both hemispheres?

Question

Take pegasus for example. Visible starting near the end of summer and continuing through autumn if you live in the Northern Hemisphere and if you are below the Equator, Pegasus is visible in late winter and through spring.

Answer 1

You can see a complete hemisphere of sky. From 45° north you can see down to 45° south, and from 45° south you can see up to 45° north, so there is considerable overlap. Constellations near the celestial equator can be seen from virtually anywhere on Earth. Pegasus is seen in the same months from both hemispheres, though the seasons are reversed.

Answer 2

This is true for all the constellations that lay along or near the celestial equator and ecliptic. For example all of the Zodiacal constellations are on this plane. The celestial equator is an imaginary line that is a projection of the earths equator onto the sky. The sun's path is observed from the Earth's reference frame, it appears to move around the Earth in a path which is tilted with respect to the spin axis at 23.5°. This path is called the ecliptic.

Therefore you can only see Orion at its highest point in the sky - its zenith (from South of the Equator) in the summer whereas Scorpius is only seen at its zenith during winter.

- There is a side note of mythology here in that Orion the Hunter could only be killed by a scorpion. Therefore they were placed in opposite parts of the sky to chase each other for all eternity...

Cheers :-)

Answer 3

From any point on Earth you can see half the sky at any given moment, the half which is above the horizon. Except close to the poles, this includes stars both north and south of the celestial equator. So stars close to the celestial equator are visible from just about any place on Earth, except close to the poles. Only right at the North Pole are you restricted to seeing only stars north of the celestial equator, and, similarly, only at the South Pole are you restricted to seeing only the southern stars. Everybody else gets a bit of a view of the stars in the other hemisphere. I live at 45° N latitude, and I can see stars down to - 45° declination.

Answer 4

Its all to do with the 'ecliptic' and the tilt of the seasonal Earth! Orion is visible high in the northern sky in your colder months, but barely visible in the south until our warmer months, Orion lies across the 'Celestial Equator'. The ecliptic! The Earth has a natural orbital tilt of 12.5 degree's to the plane of the ecliptic as it orbits the sun, which, of course accounts for our seasons! It also causes certain constellations to go below, or above this celestial equator as the Earth tilts in its orbit around the Sun! Ok?