(A) Different methods used to estimate the age of the Universe include:
- Observing the oldest known stars in the Universe and measuring their age
- Studying the cosmic microwave background radiation and using it to estimate the age of the Universe
- Measuring the rate of expansion of the Universe and extrapolating back to the point of the Big Bang
(B) A lunar eclipse occurs when the Earth passes between the Sun and the Moon, blocking the Sun’s light from reaching the Moon. During a lunar eclipse, the Earth’s shadow falls on the Moon, causing it to darken and turn reddish-brown in color. Lunar eclipses can only occur during a full Moon, and they typically last for several hours.
(C) Dark energy and dark matter are two theoretical concepts used to explain phenomena that cannot be accounted for by observable matter and energy in the Universe. Dark matter is a form of matter that is believed to make up a significant portion of the Universe’s mass, but is invisible and does not interact with light or other forms of electromagnetic radiation. Dark energy is a mysterious force that is causing the expansion of the Universe to accelerate, and is thought to make up about 70% of the total energy in the Universe.
(D) A black hole is a region of spacetime where gravity is so strong that nothing, not even light, can escape. It is created when a massive star collapses under its own weight, causing its matter to become so densely packed that it creates a singularity. Inside a black hole, the laws of physics as we know them break down, and it is not currently possible to observe or understand what exists inside a black hole.