Friday, 30 September 2016

Star magnitudes

The Greek astronomer Hipparchus looked at the heavens in antiquity and noticed that the stars were not equally bright to the naked eye. He reckoned that there were 6 levels of brightness, which turns out to the about right. He called the brightest stars magnitude 1 and the dimmest magnitude 6. On the picture of Cygnus shown, the two bigger dots are about magnitude 2 and the one at the bottom of the wing is magnitude 3. Deneb has been cut off this diagram and is magnitude 1. The modern system can use measuring instruments not eyes so is more precise and awards decimal places as well. Of course, these are apparent magnitudes because they show what it looks like. Some dim stars seem bright because they are close and some bright stars seem dim because they are distant. Scientists ahve been able to work out bright stars actually are and have calculated the absolute magnitude to compensate for this problem.

Wednesday, 28 September 2016

Hollow figures and inertia: not the centrifugal force again in Köln


So this is how they make Easter eggs! Put the hot liquid chocolate in a mold and spin it round. The chocolate tries to keep going in a straight line because it has inertia. The spinning forces act on the metal mold so they are pulled round in circles. The chocolate tries to keep going and hits the metal wall. The metal wall pushes back inwards on the chocolate: a centripetal force. The chocolate stays plastered on the edge, prevented from carrying on through the wall of the mold by this centripetal force. Many people say that the chocolate has been thrown to the outside by a centrifugal force. My Physics teacher argued otherwise but it was years before I understood why.

Tuesday, 27 September 2016

Tracking the American space program on Gran Canaria


Our coach went past the Maspalomas station at the southern end of Gran Canaria. We were told that it was used to track American space missions in the 1960s. A little research shows that it was built for the Mercury project, the first American human space flights. You can see the bases they used here https://en.wikipedia.org/wiki/Project_Mercury#Tracking_network. The orbits themselves are interesting. The mission illustrated did 6 orbits and only one went over Gran Canaria. The orbit is a wavy line on the map as a projection from 3D onto 2D and then that the Earth is tilted at 23 degrees. Orbits took 88 minutes so must have been low. Coming back to the start of the orbit after an hour and a half, the Earth had turned through about 20 degrees and the town on the ground underneath would not be the same, hence the lines don't repeat.

Monday, 26 September 2016

Learning to love constellations

I had always thought that constellations were a stupid idea. Humans seeing patterns that aren't really there. Linking together stars that are really massive distances apart in 3-D space. But I've recently spent time out at night learning my constellations. Delphinus is one that I've learned to identify in the last week. By learning the constellations I have begun to be able to find my way round the night sky. The patterns divide up the sky and make it possible for me to identify individual stars. I have found mu-Cephei in the constellation Cepheus. Herschel called it the Garnet Star. It is a deep red and is a huge red giant - they say one of the most luminous objects we can see though tiny because of how far away it is. Constellations have helped me to do this!

Saturday, 24 September 2016

Monorail at Dusseldorf Airport



I was interested in this automatic monorail and how it managed to line itself up with the exit doors on arrival. There were two sets of doors - one on the carriage and one on the station. They had to be perfectly aligned. It looks like there are strong magnets exactly opposite the doors which must be sensed by the carriage.

Friday, 23 September 2016

Watts per square metre in Wuppertal

The Schwebebahn in Wuppertal is part powered by solar panels. 558 W over 74.53 square metres means 7.4 W per square metre when the photograph was taken. I looked at a solar insolation map for Germany http://www.solarserver.com/knowledge/lexicon/s/solar-radiation.html This seems to give Wuppertal as 950 kWh per year per square metre which would give an average of 0.108 kW or 108 kW per square metre. If that's the case, we were well below average. But then I first heard of the place in the phrase "Es regnet immer in Wuppertal"!

Thursday, 22 September 2016

A smile in the sky


It's been a great summer for sundogs. These photographs were taken at Oswestry. What interested me most was the top picture. The arc was curving away from the Sun and was above my head almost at the zenith. I've seen almost complete circles of the Sun this year - there are traces above the sundog in the second picture - but they all curve concentric to the Sun.