This is a hastily put together blog on how to observe brilliant stars.
It is a rough draft at this point and I hope to gradually improve it as I learn more, however I would like to keep it fairly simple.
Generally I think there are 3 main things to determine, 1. find an area that you can get to that has low light pollution, 2. determine the state of the moon, 3. determine the weather conditions.
1. Determine a location with low light pollution
Go to here:
http://www.lightpollution.it/worldatlas/pages/fig9.htm
and download the high resolution tiff for your region of the earth.
Determine the nearest accessible location near you where the light pollution is the lowest.
As an example below is a crop for southeast Australia of the dark sky map.
Red indicates the most light pollution with black the least. The three biggest light pollution are (from left to right) Adelaide, Melbourne, and Sydney. In Victoria the map indicates that the least light pollution occurs in the northwest and through the eastern Australian Alps into east Gippsland. Some examples from NW Victoria are presented in the video below on my 2016 bike tour.
However note that Wilsons Prom sticks into the black and it is certainly has beautiful stars.
You should not lose hope of seeing nice stars in the areas of light pollution, even in Melbourne you can see some stars. One of the interesting places was French Island. There you are surrounded by light pollution, however the island itself has virtually none. There is a sense of being in a hole of light pollution.
2. Determine the moon rise/set times, and phase
Your night sky view will be strongly affected by the presence and phase of the moon. Because reflects so much sunlight (to the point where you can see your shadow, and even rainbows at night “moonbows”). There are many sites to see the moon phase and the rising and setting times, below is a nice example for Victoria, Australia.
http://moonphases.willyweather.com.au/vic/central-highlands/ballarat.html
For the best stars view before the moon rise or after the moon set. Or if there is a new moon or a crescent moon the impact of the moon will be less than a gibbous or full moon. Below is an example for the time of writing. For the night of 22/23 June the moon sets at 1046 pm and does not rise until daytime the next day. Therefore anytime after 1030pm is probably best for stars, still get out early to enjoy the moonset.
3. Forecast the weather
No matter what the light pollution is like you will see nothing if it is cloudy. The first thing you need is a clear sky. Clear skies tend to occur in high pressure systems but not always. Also clear skies can occur associated with low pressure systems. So we need to be able to predict the clouds.
Cloud prediction
The best method for predicting the cloud cover for the nights ahead is to look at weather models. I will use the available models for Australia as an example. The two easiest to access are ACCESS (see what I did there) and GFS. ACCESS is probably the best predictor as it is developed by the Bureau of Meteorology and may benefit from better land surface and observational data. The GFS is from the Americans and while it appears to be less accurate than ACCESS for Australia it has the benefit of better open access that has allowed individuals to output more useful plots for weather prediction.
GFS: http://forecasts.bsch.com.au/stormcast.html
For the GFS click the link above then select the time and day on the left that you plan to observe the stars. Then click on “COMPLETE CHARTS LIST” and in the drop down menu select “total cloud cover”. This will give you the total cloud cover as a percentage of the sky. You can also see the cloud cover for different levels in the troposphere if you desire.
ACCESS: http://www.bom.gov.au/australia/charts/viewer/index.shtml
For ACCESS click the link above. You can also zoom in to your particular area using the “area” drop down menu. Unfortunately, unlike the Brisbane Storm Chaser’s GFS plots, you will not find a total cloud cover variable available for plotting. However do not despair we can check for clouds at five levels in the troposphere that should help to corroborate the GFS total cloud cover. To do this we need to determine if the air is saturated at any of the levels which would suggest cloud cover at that level. For this select “Relative Humidity” from the “Show” drop down menu. First you can check the surface. If your observing area is indicating 100% or near 100% relative humidity at your time of observing there may be a risk of fog or haze that might obscure your view of the stars. If it is foggy in the valley it may help to head up any nearby hill or mountain. Now check the other 4 available layers (850hPa, 700hPa, 500hPa, 200hPa) for their relative humidity to determine if it is near 100% at any of the layers. Looking at each of these levels is not full proof as there could easily be a cloud layer in between one of the levels. This is why you must look at the GFS total cloud cover in addition to the ACCESS relative humidity fields.
Other things worth thinking about are wind direction, dust and pollution levels. The presence of nearby fires. If the air is blowing from a region where there are large cities then pollution blown in may reduce the visibility of the stars. The same could apply for dust. I also heard that sea spray can reduce star visibility so if there is a gale blowing off the ocean you may find that even though the air is wonderfully clean that salt from sea spray somewhat impairs viewing.
Suitable locations within weather systems
High pressure systems
As mentioned above, high pressure systems are often associated with clear skies and good observing conditions. However you will need to check that fog is not forecast because in some locations (like Canberra, Australia) fog frequently occurs as the land cools down at night and cools the air to its saturation point (dew point temperature).
Low pressure systems
There are various types of low pressure weather systems (extratropical cyclones, subtropical cyclones, tropical cyclones, polar lows, etc.) and they all tend to be associate with clouds and precipitation which are not good for observing stars. However it is not all bad news as there may be particular areas within the systems that are nice and clear. Below I will discuss a couple of examples, extratropical cyclones and tropical cyclones.
Extratropical cyclones
Here I am referring to a typical mid-latitude system, or extratropical cyclone (https://en.wikipedia.org/wiki/Extratropical_cyclone). Below is the surface pressure map for Australia at the time of writing.
Looking at the satellite imagery the regions of clear sky are indicated in the post cold front and high pressure regions in the image below. However this is a visible image during the day and these are not available at night because it is dark. At night use the infrared image (next one below)
Tropical cyclones
rather than a tropical cyclone. In a full on hurricane you may get good night skies in the days preceding the storm (and maybe afterwards) because of descending air around the storm clearing the clouds. In a mid-latitude storm system your best chance of clear skies is probably after the cold front has past. The advantage of this may be that the air is also very clean depending on your location, but watch out for some post cold front showers.
Determining the position of the Milky Way
There is a great interactive star map on Sky and Telescope, you have to register. The link is on the top middle of the home page.
You can use various apps for determining star positions such as Skymap for Android and similar ones for IOS. These popular apps have been around for a while and are well known but still represent some of the most impressive uses of mobile technology from the tilt and GPS features. Skymap’s time travel feature allows you view other days and times.Search for either Sagittarius, Ophiuchus, and Scorpius to find the galactic centre.
Find out more
About the three types of light pollution:
Find your region of least light pollution.
http://www.lightpollution.it/worldatlas/pages/fig9.htm
Please comment with suggestions, links, errors and I will update this blog.
youstorm 