Author Archives: Allen Versfeld

About Allen Versfeld

Allen is an amateur astronomer, an IT professional, a podcaster, a father of five growing kids, a barely competent chess player, and the owner and publisher of the Urban Astronomer podcast and website. He has formerly served as Director of the Astrophotography and Citizen Science sections of the Astronomical Society of South Africa. You can find his personal social media feed on Mastodon!

How hot is the Sun?

Urban Astronomer avatarPosted on by

The surface of the Sun is usually around 5800 degrees centigrade, but is a blistering 13.6 million degrees at the core.  The core is where the nuclear reactions happen, with hydrogen atoms fusing together to make helium, and this is what powers the Sun and creates all the heat.  The outer atmosphere of the Sun, called the chromosphere and which is only visible during a Solar Eclipse, has a temperature of about a million degrees, with occasional heat-waves all the … Continue reading →

How far is the nearest star?

Urban Astronomer avatarPosted on by

Is this a trick question?  Because, strictly speaking, the Sun is a star.  The Sun is roughly 150 million kilometers away.  But the normal English usage of ‘star’ refers to things that only come out at night.  In that case, the nearest star is Proxima Centauri, a red dwarf positioned 4.2 light years away in the southern constellation of The Centaur.  It is a member of a bright triple star system, but is not visible to the naked eye itself. … Continue reading →

What is a star?

Urban Astronomer avatarPosted on by

A star is a vast sustained nuclear explosion at the centre of an enormous sphere of superheated gas (or plasma).  The Sun is the nearest star to Earth.  Massive clouds of hydrogen gas (often laced with trace amounts of heavier elements) start condensing through various mechanisms until they’re dense enough for gravity to start drawing the cloud in upon itself.  As it contracts, the temperature and pressure begin to rise.  After a while the cloud will be so dense and … Continue reading →

New moons discovered around Jupiter

Urban Astronomer avatarPosted on by

As of 1 June 2011, the count of known moons orbiting Jupiter has increased from 63 to 65.  The new moons, designated S/2010 J1 and S/2010 J2 are really tiny at 2km and 1km across respectively.  They also have irregular orbits, moving the wrong way around Jupiter at steep angles, indicating that they were not part of Jupiter’s original set of satellites, but comets or asteroids that had been captured by Jupiter’s immense gravity.  Any bets on when the next … Continue reading →

Earth could be removed from global time standard

Urban Astronomer avatarPosted on by

For as long as we’ve kept track of time, we’ve needed astronomy.  A year was defined by the time taken for Earth to complete one revolution of its orbit around the Sun, a day was defined by the time it takes the Sun to make one full circuit of the sky, and all other units were derived from these two.  An hour is one twenty fourth of a day, a minute is a sixtieth of an hour, and a second … Continue reading →