The estimated distance of the Andromeda Galaxy from our own was doubled in 1953 when it was discovered that there is another, dimmer type of Cepheid. In the 1990s, measurements of both standard red giants as well as red clump stars from the Hipparcos satellite measurements were used to calibrate the Cepheid distances. This violent …[Continue reading] Andromeda Galaxy
Earth is the third planet from the Sun and the only astronomical object known to harbor life. According to radiometric dating and other evidence, Earth formed over 4.5 billion years ago. Earth’s gravity interacts with other objects in space, especially the Sun and the Moon, which is Earth’s only natural satellite. Earth orbits around the …[Continue reading] The Earth
The Moon is an astronomical body that orbits Earth as its only natural satellite. It is the fifth-largest satellite in the Solar System, and the largest among planetary satellites relative to the size of the planet that it orbits (its primary). The Moon is, after Jupiter’s satellite Io, the second-densest satellite in the Solar System …[Continue reading] The Moon
