They reflect light from the Sun.
They reflect the Suns light back to Earth
The constellations of the zodiac fall on the plane of the ecliptic (the plane in which the Earth orbits the Sun) and all the Sun's planets orbit also in the plane of the ecliptic. This means that ALL the planets eventually move through ALL the zodiacal constellations (as seen from Earth). It also therefore follows that the planets are never seen in the non zodiacal constellations.
Venus has phases that can be seen from Earth. See related link for a pictorial.
Every now and then
All of the planets can be seen from Earth, but a telescope or a powerful set of binoculars may be needed to see Uranus and Neptune. All of them cant be seen at certain times, when they are on the opposite side of the solar system on the other side of the sun for example.
Earth
They reflect the Suns light back to Earth
The constellations of the zodiac fall on the plane of the ecliptic (the plane in which the Earth orbits the Sun) and all the Sun's planets orbit also in the plane of the ecliptic. This means that ALL the planets eventually move through ALL the zodiacal constellations (as seen from Earth). It also therefore follows that the planets are never seen in the non zodiacal constellations.
The part of the Moon which receives......can be seen from the Earth.
no planets crust does not have light of their own but the core of the earth has light of its own
Venus has phases that can be seen from Earth. See related link for a pictorial.
None. The moon is closer than the other planets, so it will obstruct other planets.
Venus and Mercury
we can see 6 planets mercury venus mars jupiter saturn
Inner planets orbit inside the orbit of the Earth, can only be seen in the morning or evening sky and are never seen as full disks form the Earth. Outer planets orbit further out than the orbit of Earth and can be seen from time to time as full disks in 'opposition' or overhead at midnight.
That is sometimes what the Moon is called. Seen from Venus the Earth and Moon would be seen as a pair of bright planets up to 0.5 degrees apart at opposition, which is the diameter of the Moon as seen from Earth.
There are 5 planets that are visible to the naked eye and can be seen without the aid of a telescope. These planets are Mercury, Venus, Mars, Jupiter, and Saturn.