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!
I managed to complete and submit the assignment this morning, leaving me free to keep my promise. Not a whole lot got done – only three wets and a whole lot of getting to know my mirror again under a bright light. I’m doing something that never occurred to me before: Find pits, mark them with a permanent marker, then photograph the mirror. Do a few wets, then repeat, and compare photographs. Much easier to keep track of which pits … Continue reading →
There are about 6000 stars in the night sky that are visible to a healthy adult standing in a properly dark location. Of course, you can never see more than half the sky at a time, so to see all of them you would need to live in the tropics and spend some time looking upwards regularly — it takes a full year for the entire sky to pass overhead. So at any one time, there’s something between 2500 and … Continue reading →
Trick question! The Earth weighs nothing at all, but itdoes have a mass of 5.9×1021 kilograms (or in regular figures: 5 900 000 000 000 000 000 000 tonnes). Why the difference? Mass and weight are actually two totally different things. If you think about astronauts orbiting the Earth in the International Space Station, they float around totally weightless. Yet they still have mass and inertia. Weight only exists when something resists the pull of gravity – usually, on earth, … Continue reading →
You need to know that the Earth’s axis is not nicely aligned with the Earth’s orbit – it’s tilted from the vertical by about 23 degrees. So as the Earth moves around the Sun, one of the poles is leaning towards the Sun. For six months it’s the north pole, and for six months it’s the south pole (This affects how much sunlight each side of the world gets, and causes the seasons). The day of the year when each … Continue reading →
Time flies when you’re having kids. In the last entry, I promised to wait no more than a single month before unpacking my mirror and resuming grinding. I now see that I have only two days left, and am not ready! But I haven’t been lazy. In that time, my wife has had a baby, my plumbing has sprung multiple leaks (and in a separate incident, had the geyser burst) leading to my landlord’s cut-rate plumbers tearing open half the … Continue reading →
