Horizon = the line at which the earth’s surface and the sky appear to meet.

• The sun rose above the horizon.
• The moon began to rise slowly above the horizon.
• It’s beautiful to watch the horizon at the sunset.
• At the sunrise the sun looked like a ball of fire above the horizon.

Horizons = (plural) the limit of a person’s knowledge , experience or interest, perception etc.

• He wanted to change his outlook and broaden his horizons.
• The discovery will open up new horizons in the field of cancer research.
• His decision to go to University will certainly broaden his horizons.
• His stay at Chicago has broadened his horizons.
• As your horizons expand , new ideas will become acceptable to you and there will be a transition from your orthodox stand and approach.