• Tag Archives Astronomy
  • Navigation by the stars: finding south

    For thousands of years travellers would use the stars for navigation.

    Here in the southern hemisphere we can easily find our way when lost at night by learning to find the constellation of Crux (the Southern Cross) and the Pointers (Alpha and Beta Centauri).

    Draw two imaginary lines, one through the Southern Cross and the other perpendicular to a line joining the two pointer stars. Where these lines meet is known as the Southern Celestial Pole. Look directly towards the horizon below this point and you will be facing south.

    Finding South

  • Get to a dark site

    Picture saved with settings embedded.
    Milky Way – Image taken Busselton WA – copyright Mark Davies – Earthside Astronomy

    Recently I gave a talk, educating the general public about light pollution and the effects on Astronomy, Wildlife, People and the Economy.
    I was a little shocked to find that 2/3 of the audience had never even been to a dark site or even seen the Milky Way.

    For thousands of years people would look up at the night sky and be inspired by the absolute immensity of the cosmos. Now due to the increasing number of poorly shielded and misdirected city lights we generally don’t look up any more, when we do, we are lucky to see a few hundred stars.

    Lets get some figures to get a sense of scale. Astronomers have calculated that there is on estimate 100 – 400 billion stars in the Milky Way alone. This is based on determining the  mass of the galaxy then extrapolating the number of stars based on an average mass. As we can safely assume that the majority of stars are smaller red and brown dwarf stars the number would be closer to the 400 billion.

    The glow from these stars and the ionised gas in the disk of the Milky Way allows us to see the spectacular view of the sky as shown in the image above but to see this you need to get out of the urban sky glow and into some dark country locations.

    The next obvious question you are going to ask is “where can I go to get dark skies?”

    To get the truly dark skies in Perth you will want to drive east for a bit over two hours to get to somewhere such as Pingelly or Cunderdin, however for general purposes anywhere in the blue to white region of the map below will provide you with a fantastic view of the night sky.

    A favourite site of mine is the Avon Valley National Park which is still in the blue region and only about 45 minutes from Perth.

    One final word of warning if you are planning on a dark sky expedition. While you can get away from the city lights, you will be hard pressed to get away from moon light so try to organise your trip around a new moon to maximise your experience of the dark night sky

    Image courtesy of http://darksitefinder.com/
    Image courtesy of http://darksitefinder.com/


  • Choosing your first telescope

    One of the most common questions I get asked is  “I am looking at buying my first telescope, what should I get?”

    Well, the instant reply is: what do you want to use it for and what is your budget?

    Generally I would say that a telescope is used for three main purposes, with solar observing the exemption.

    1. Viewing the moon, planets and bright stars
    2. Viewing deep sky objects (DSO)
    3. Astro-Photography

    If you are buying a telescope for a young child or are not going to get too serious into your astronomy hobby, you will be going for option 1.

    Option 1: Basic AZ Refractor
    Option 1: Basic AZ Refractor

    Get yourself a fairly cheap $250-$450 AZ or EQ mount refractor or reflector telescope, Sky Watcher / Celestron / Orion brand and you will pull this scope out from time to time and enjoy the view.

    Absolutely do NOT be tempted to spend less than $100 on a cheap Tasco, Australian Geographic or no-name brand of refractor scope as the mount will be that flimsy that a small breeze will have the scope shaking and the unit will be in the cupboard never to be used again.

    If you are going to be a bit more serious, you will want to start viewing DSOs, including nebula, star cluster and even other galaxies and will go for Option 2.

    When viewing these fainter objects the most important feature to your telescope is aperture. In a refractor, this is the size of your objective lens (the big one at the front of the optical tube assembly (OTA).

    In reflector and Cassegrain telescopes, it’s the size of your primary mirror (the mirror at the base of the OTA).

    Due to cost and manufacturing limitations you will be going for either a Newtonian or Cassegrain telescope at this point.

    Cassegrains are excellent scopes, especially if you are planning on spending more than $2500 on your scope/mount combination, but for your first visual observing scope you will not be able to go past a Dobsonian Telescope for bang for your buck.

    Option 2: Dobsonian Telescope
    Option 2: Dobsonian Telescope

    The Dobsonian is basically a large Newtonian reflector telescope, mounted on a very low-cost, chipboard, lazy susan.

    Dobsonian telescopes come off the shelf in sizes from 6″ to 16″ costing between $380 and $4400.

    I personally started with a 10″ manual Dobsonian which is a good size costing around the $1200 mark for the base model.

    A fairly recent innovation in the Dobsonian design will even allow you to computerize this telescope and skim through a list of about 42000 objects and the telescope will automatically move to find the object for you and will track the object across the sky.

    No more nudging the scope every minute or two. Bliss.

    While being an excellent scope for visual observing, if you are in the Option 3, category this is not the scope for you. At this stage what you really have to look for is a solid, motor drive equatorial mount.

    This will help you to track the sky while taking long exposure photos.

    When choosing a scope for imaging the aperture is not always as essential, although it always helps.

    With imaging you will now be taking photos leaving the shutter on your camera open for minutes at a time gathering all the light which hits the photo receptor over this period and storing it in a single image, then processing the image or set of images in Photoshop or the likes.

    I have seen images taken using an 80mm refractor which are just as breathtaking as images from a 14″ Cassegrain

    The realms of gear for astro-photography are almost endless, but for the purpose of this blog let’s have a look at a basic starter package.

    Option 3 EQ Telescope (minus camera)
    Option 3 EQ Mount RC 6 Telescope (minus camera and auto guider)
    • A decent equatorial GoTo mount will set you back in excess of $1,500
    • A 6″ Ritchey-Chretien Cassegrain will be around the $450 mark
    • For a camera, you will be able to start with a basic DSLR for about $500
    • And finally a mini auto guider package will set you back around $500

    So for under $3,000 you will get a good start with your new astro-photography hobby.

    Please note however this is in no way the only or even ideal imaging setup. If you want to get into Astro-imaging for the first time I highly recommend joining a local astronomy group such as Astronomical Group of Western Australia (AGWA). This group and many like it have a keen and willing member base that will gladly assist you.

    Getting serious in Astronomy hobby is not the cheapest idea, but, personally, I will never get enough of viewing the Orion Nebula or the M22 Globular Cluster and the joy I can get from showing a first timer these views.

    Author: Mark Davies