Category Archives: Astronomy 101

One of my main goals is to try and share a bit of knowledge and understanding about the incredible universe. I have been steadily writing and posting various articles to explain and educate the masses (that’s you, dear reader!) a bit more about some of the science behind the hobby. An urban astronomer might never see most of the things we talk about here, but it’s still good to know about them.

Why can’t you see any stars on the moon?

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Ah, but you can if you wait till night time!  You can’ t see any stars in photographs taken from the Apollo missions because they were all taken in broad daylight.  As any photographer will tell you, a camera can only cope with a narrow range of brightnesses, so that the aperture setting and shutter speed are very important if a photograph is not to be over- or under-exposed for given lighting conditions.  In this age of automatic point-and-click digital … Continue reading →

How hot is the Sun?

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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?

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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?

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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 →

Seasons

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Summer, Autumn, Winter and Spring.    The cycle of the seasons has been known since the dawn of time and human beings all over the world use them to mark moments in their personal histories.  Some people are astonished to learn that the seasons are six months out of phase on opposite sides of the globe, something which amuses us in the Southern hemisphere no end.  But what actually causes seasons?   Many people are dimly aware that the Earth’s … Continue reading →