Mercury takes 88 days to orbit around the Sun, which means that one Mercury year lasts less than three Earth months. Mercury has such a short year because it is very close to the Sun. According to Newton’s Law of gravity, this means that the Sun’s gravity is much stronger at Mercury than it is for Earth, and this requires it to move a great deal faster if it is to stay in its orbit, which is why it has … Continue reading →
Planetary nebulae are clouds of dust and gas ejected from older stars as they move on to the next stage in their evolution. When a star uses up all its hydrogen fuel, and begins to burn helium, the core heats dramatically, causing the outer layers of the star to inflate dramatically. The outer layers of the star escape its gravity, and the solar wind of high energy particles and radiation accelerates the still superheated plasma out into space where it … Continue reading →
Globular clusters are clusters of stars, arranged into a sphere. They contain tens of thousands of stars, packed very closely together, so that when viewed from the Earth, their core’s appear as a single glowing mass. Globular clusters are arranged in a vast spherical halo around their parent galaxy. Our own Milky Way galaxy has a little over 150 globular clusters, but larger galaxies can have many more than that. They tend to be very old – at least as … Continue reading →
Dear Urban Astronomer Thanks for all your interesting celestial tidbits, which my hubby and I enjoy very much. We are just viewers and treasurers of the skies we love so much, not a professional like you! Could you perhaps enlighten us about a very bright star which is currently to be seen approx 30% up from the horizon to the east. When we say to the east, it is where our sun sets during the winter season. The star … Continue reading →
As of February 2024, we know of sixteen moons orbiting Neptune. The largest, Triton, was discovered only 17 days after Neptune itself was found in 1846 and it would be over a hundred years before any others were first seen. Triton is one of the larger moons in the Solar System with a diameter of 2700km, and orbits backwards around Neptune. The most recently discovered moon, by contrast, is less than 8 km across. No doubt there are more … Continue reading →
