Moon | Diffraction Grating View

I headed home after attending the public lecture on aurorae by University of Iowa professor Craig Kletzing. One part of his talk included a demo of color emissions from the element oxygen. It is responsible for nearly all the colors associated with aurorae. We needed diffraction grating glasses to see the demo effect such as these.

As I drove home, I noticed the bright crescent Moon. I stopped the car to look through my grating glasses. Once home I set up the camera with the grating over the lens. It was a nice way to end the day.



Stars | How They Change Over Time

Stars go through changes over the course of their existence. The rapidity and violence of those changes depends upon the mass of the star. Low mass stars are slow to change. High mass stars change quickly. Perhaps a case of Live Fast, Die Young.

This post is intended for those readers who have wondered what happens during the lifetime of a star. It is not intended to be an exhaustive description of the life-cycles of stars. Some of the numbers used here represent a range of values assumed for these events. Sources will differ some. There are many parts of star behavior that are complicated and not understood well by the experts. General concepts are presented here to make the processes more understandable.

All stars involve two types of processes that oppose each other. Gravity pulls the star components inward and tries to reduce the star’s volume. Nuclear fusion exerts outward forces and tries to increase the star’s volume. This interplay of opposing forces can create equilibrium. Change in strength of the processes will cause the star to either expand or contract in size. Since the mass of the star is quite constant, the inward pull of gravity is constant. The outward forces can change in strength as nuclear fusion processes change.

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Gravity Waves | Both LIGO Record Them

A little more than 1.3 billion years before 14 Sep 2015, a pair of 29 and 36 solar mass black holes orbited each other, slowly getting closer together. On that date, they merged into one black hole of 62 solar masses. Their merger radiated 3 solar masses of energy in a fraction of a second.

This animation from Simulating Extreme Spacetime SXS uses calculated effects from the equations of Einstein to simulate the view of the star field behind the black holes. Imagine you are close enough to watch their dance. Paths of starlight are altered by the masses of the black holes. It is also greatly slowed down. The black holes were actually moving a high fraction of the speed of light as they orbited just before merger.

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Lunar Eclipse | Images | Tetrad Part 4

We left central Illinois well before sunset. It was overcast. The prospects for seeing the lunar eclipse were not very good. As we headed northwest toward our home in eastern Iowa, the skies showed signs of improvement. Minutes before the Sun set, it shined brightly through a big opening in the clouds. That was a good sign.

Driving west on I-80, we could see brightness in the east behind the few remaining clouds indicating that the full Moon had risen. We stopped for a driver change. There was the Moon just entering the shadow of the Earth. I periodically rotated the rearview mirror up to take a peek at the eclipsing Moon behind us. Eclipse in progress.

After we unpacked the car, I put my camera on a tripod on the front porch. This first shot showed the Moon about 50% into the umbra. Notice the curve of the Earth’s shadow. It gives a sense of the relative sizes of the Moon and Earth.


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Lunar Eclipse | 27 Sep 2015 | Tetrad Part 4

Previous posts about this tetrad of lunar eclipses can be found by following this link. Visit those links for explanations of the phenomenon if you need them.

Part 4 of this tetrad takes place Sunday evening 27 Sep 2015 for North and South America. First evidence of the partial phase begins at 8:07 pm central daylight time. The total eclipse phase begins about an hour later at 9:11 CDT. Totality lasts a little more than an hour ending at 10:23 CDT.

The timing of this lunar eclipse is very good for viewers in North and South America. It begins when most people are still up. If sky conditions are not overcast, it will put on a show all evening. You do NOT need eye protection.

You don’t have to watch it continuously. Look every 20-30 minutes. You will see the Moon change color and coverage as it transits Earth’s shadow.

8 Oct 2014 | 5:56 am | f/2.8 | ISO 200 | wb daylight | 2 sec | J. Ruebush


This is also a supermoon. It will be about 7% larger than normal because it will be closest to Earth in the slightly non-circular orbit. You will not likely notice it unless you have two photographs to compare such as these.

Regular full moon vs supermoon comparison Source: Karen Roe via

Regular full moon vs supermoon comparison
Source: Karen Roe via


NASA posted this short video to explain what to watch for and when. May your skies be fair.

Saturn | @ Opposition May 23 2015

What does it mean for a planet to be at opposition? From our Earth perspective, the Sun and the planet are in opposite directions in the sky. The moment the Sun sets in the west, the planet rises in the east. Saturday May 23 is opposition day for Saturn. The illustration below shows a thin yellow line from the Sun through Earth to Saturn. Visit to play with the interactive for this image.


Dominic Ford | In-The-Sky

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Gravity | How It Behaves

There are two astronauts somewhere in space, 3 meters apart, and not moving relative to each other. Astronaut Lucy has a total mass of 100 kg including her suit. Astronaut Ricky has a total mass of 140 kg including his suit. Question 1 – Is there a physical attractive force between them? Question 2 – What are the variables which affect the strength of that force? Question 3 – How large is that force? Those questions will be answered in this post.


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