Archive for February 12th, 2012

Essential amateur astronomy equipment

Sunday, February 12th, 2012
Planisphere and a torch with red filter.

I thought I would share with you some of the basic equipment that I consider to be essential when starting amateur astronomy.

In reality you need no more than your eyes, but you will soon want to be more methodical than just looking up at night.

My bare minimum equipment is as follows:

  1. Planisphere: an instrument that can be adjusted to display the stars at a given date and time. This is very useful for planning your sessions as well as navigating your way around the night sky.
  2. Torch: fit the torch with a red filter. I use a mini Maglite that can be fitted with a purpose build plastic filter. Other methods include painting the bulb red or attaching a red plastic sweet wrapper over the end of the torch fastening it with elastic bands. Red light effects your night-vision the least. You need a torch for checking star charts and making your observation notes.
  3. Cartes du Ciel: this is a free planetarium programme for your computer. There are versions for Linux, Mac OS X and Windows. Cartes du Ciel allows you to make star charts that can help you plan your sessions. It is quite easy to use and quite accurate.

    If you have a laptop you can take Cartes du Ciel outside with you, it has a night vision mode.

    The power of planetarium programmes is that they allow you to track the planets and the Moon. The planisphere cannot do that.

  4. A sky atlas: charts of the constellations, locations of deep sky objects etc. I use Philip’s Atlas of the Universe by Patrick Moore. This book has nice charts of the constellations. There are plenty of other good books that have very usable charts.
  5. A compass : You will soon learn which way is North by the position of the stars. Until then a compass will help orientate yourself. I always have a compass to hand while observing, just in case.

Other things to be aware of is the weather and the temperature drop at night. Dress appropriately, take a woolly hat and gloves.

My Telescope: Bresser Skylux NG 70-700 refractor

Sunday, February 12th, 2012
My Bresser Skylux NG 70-700 refractor I own a small telescope, the Bresser Skylux NG 70-700 refractor. I have used it to view the moons of Jupiter, the phases of Venus, the Andromeda galaxy and the Orion Nebula. The most impressive, and I think what the telescope is best for is observing the Moon.

For your enjoyment, I have taken a few pictures of the telescope.

The telescope has an aperture of 70mm and a focal length of 700mm.

I changed the original finder scope to a laser finder. The original finder scope I found to be difficult to use, it has poor focus and thus I was unable to find anything but the very brightest stars using it.

The mount is a EQ3 mount. I found the mount easy to use and quite steady.

As I have already stated, I changed the finder scope to a laser finder. This does not magnify the sky, but places a clear red dot in the viewer. I find this much easier to use than the more traditional cross-hair finder scope.

I have used this telescope for basic astrophotography. In particular I have taken fairly good pictures of the Moon directly through the eyepiece using a rather modest digital camera.

I tend to couple this with a Moon filter which helps with the contrast and helps stop the features on the Moon getting washed out. You can find one of my Moon pictures in an older post here.

The telescope came with three eyepieces: 20mm, 12mm, 4mm. This gives magnifications of 35x-262x. This covers “sensible” magnifications for this telescope. Sometimes cheaper poorly made telescopes come with eyepieces that are unsuitable, this is not the case with the Skylux NG 70-700.

Although the telescope is quite portable I tend to use it in my back garden, which is far from a dark sky site.

This telescope was a Christmas present from my wife back in 2008.

Pure Energy?

Sunday, February 12th, 2012

People often talk about “pure energy” in rather an informal way. In truth there is no proper notion of pure energy. Loosely one often means photons when the term pure energy is used. For example, you may come across statements like: when matter and antimatter collide they annihilate producing pure energy.

Energy is a property of “stuff”; that is a physical system. A configuration of a physical system will have a property that we can indirectly measure, which we call energy. One cannot have energy as some independent “thing”.

As an analogy, you may talk about the colour of a car. Lets say a red car. Being red is a property of the car. One cannot talk about “red” as some notion independent of the objects we see as red in colour. Red does not exist by itself.

So, what is energy?

Informally energy is understood as a property of one physical system that allows it to preform work on another physical system. In essence this means that energy is the property associated with movement or change. It is the “doing” property.

Not that the above tell you what energy is. However, this is not really a problem as physics tends not to deal with the metaphysical notion of existence and what is. Physics deals with mathematically modelling nature. With that in mind, one should keep close the quote (I paraphrase) I believe is due to Feynman:

Energy is a number we can calculate at different points in time and find the same value.

That is energy is something we can calculate, given some configuration of a physical system and (given some technical stuff) we see that the energy does not change in time. That is, it is conserved.

A little more mathematically

We have a very powerful and beautiful theorem that relates symmetry and conservation laws.

Noether’s first theorem: Any differentiable symmetry of the action of a physical system has a corresponding conserved charge.

This theorem is at the heart of modern physics and is based on the calculus of variations.

What does this theorem mean?

Theorems as theorems are by their very nature technical. But we can informally understand some consequences of this statement quite easily.

If the mathematical description of the physical system does not alter upon changes in time then there is a conserved quantity that we call energy.

This is as close to answering the question what is energy? as you can really get. Energy is the quantity that is associated with a physical system not explicitly depending on time.

The caveat here is that the physical system not depend explicitly on time. This is generally reasonable. From a physical perspective this seems natural, any experimental outcome should not depend on when you preform the experiment. Because you get the same result today as you will tomorrow, energy is conserved.

Back to pure energy

I hope I have explained that the notion of “pure energy” is not well founded. Energy is a number that is associated with physics not changing on when you preform your experiments.

Noether’s first theorem makes this association with time and energy explicit. Other common conserved quantities exist:

Symmetry Conserved Quantity
Translations in Time Energy
Translations in Space Linear Momentum
Rotations in Space Angular Momentum

In the same way nobody talks about “pure angular momentum” as some thing in its own right, no one should use the term “pure energy”.