In 1603, Johann Bayer (A German astronomer), introduced a system of ranking stars on their apparent magnitude. He assigned each star in a constellation a Greek letter, with Alpha being the brightest and next brightest star being Beta, etc. Many people think of stars in a constellation as being close to each other in actual physical existence. This, in most cases, isn’t the case; stars in constellations only appear to be next to each other because of the angle we view them from when looking at them from Earth. Stars usually are millions of miles away from each other in reality.
Planning
Location
I plan to take photographs of 3 constellations from house garden which is located in Carlton, Nottingham (Suburbs). This is admittedly not the optimum observation location due to slight sky glow caused by street lamps and lights from neighbouring houses. It is; however, better than being close to the inner-city which would undoubtedly prove to have a significantly larger amount of light pollution. An ideal location would be somewhere further away from the city centre, preferably in the countryside where there would be close to no sky glow which would allow for better and unhindered observations. Unfortunately this option isn’t available to me due to travel and other reasons.
Date & Time
I have chosen to do my observations in late April which is when the moon will be nearing its ‘New’ phase (29th specifically). When there is a new moon, its illumination to the surrounding sky is at its lowest which will allow for better observations. I have also chosen April because there are some interesting constellations to be seen that are most visible in the month of April. I will need to research the weather conditions in order to find the most appropriate days to observe; days with clear enough visibility which will allow me to determine the colour of the stars.
The time at which I will perform the observation will depend on the moonset time for that particular date; with the moon below the horizon its potential illumination will be minimalized. I will collect this data from an online moon rise/set calculator3
Equipment list for observation
- Red filter torch (To allow me to see without effecting my eyes adaptation to the dark)
- Camera & tripod (Fuji finepix s2980. Exposure time set to 8 seconds which is not too long that it will cause star trails but long enough so it will let in enough light for good visibility. I have widened to aperture to maximum F3.1 which allows more light to get into the lens. ISO is set to 400). This isn’t the best camera possible for astrophotography but it is the best I have available to me.
- Map of late April Sky
- Warm clothes
- Flask of coffee
Sky Chart
This is a sky/star chart of1 what the night sky will look like during late April at around 11pm (The period in which I will make my observations)
After taking my photographs, I will digitally enhance them using Adobe Photoshop2 in order to increase the visibility of the stars which will allow for better analysis.
Using an online resource3, I have found on which date(s) the moon will be new or close to being new. I have also checked for visibility levels using a weather forecast4.
After evaluating the data I have acquired, I have chosen to perform the observations on 27th,28th and 29th of April as these dates include or are near to when the Moon in new. These are also the dates where the Moon is least illuminated, which is ideal for observation as a highly illuminated moon could have adverse effects on my photography due to skyglow.
Constellations
This is a list of constellations I could potentially observe for my investigation, taken from the star chart:
- Ursa Minor
- Ursa Major
- Cassiopeia
- Auriga
- Leo
- Cepheus
- Boötes
After assessing all the possible constellations I can photograph, I have chosen three:
Ursa Major
I have chosen to observe this constellation mainly because of its asterism known as the Plough or ‘The big dipper’. This asterism is useful in locating other constellations or stars; Dubhe and Merak form a pointer towards Polaris (The North Star) whilst Megrez and Phecda form a pointer towards Leo, which is another constellation I have chosen to observe. Ursa Major contains seven Messier objects: a double star (the first binary system to be discovered, in 1650), a planetary nebula, an irregular galaxy and four spiral galaxies. Ursa Major is also a constellation best seen in April allowing for easier colour identification and photography. I will use this diagram5 to help me identify the stars in the constellation
Leo
The Leo constellation is another constellation best seen in April. It features Regulus, which is a significantly bright star (25th brightest in the sky) allowing me to easily identify and photograph it, as well as determining its colour. Leo also contains many interesting messier objects such as four spiral and elliptical galaxy. This labelled diagram6 will help me identify the individual stars when stating observed colour and magnitude
Cassiopeia
Cassiopeia is a northern circumpolar constellation, so it can be viewed all year long. It is also prominent in the sky due to the brightness of its stars and formation of the letter ‘W’. This labelled will help me to identify each star7.
Reference stars
In order to determine my estimates for the magnitudes and colours of each of the stars I observe, I am going to use the known magnitudes of stars as a reference. Here are the stars I have chosen from each constellation.
Observation
Several photos of each constellation were taken over the three days; I then selected what I thought were the best photos for each. The camera settings previously stated were kept the same for all photos.
(Fig.1)
(Fig.2)
(Fig.3)
Analysis
Using the known magnitudes and colours of a star in each constellation, I compared these with the surrounding stars to estimate their colours and magnitudes to the nearest whole number.
Ursa Major (Fig.1)
Magnitudes obtained from Starryskies website11
Leo (Fig.2)
Magnitudes obtained from Leo Wiki Page12
Cassiopeia (Fig.3)
Magnitudes obtained from Cassiopeia Wiki Page13
Evaluation
Quantitative accuracy
My magnitude estimates were:
- Too high 29.4%
- Too low 11.7%
- Correct 58.8%
Accuracy for each constellation
-
Ursa major - average of 0.3 away from actual magnitude
-
Leo – average of 0.48 away from actual magnitude
-
Cassiopeia – average of 0.5 away from actual magnitude
Although there were a considerable amount of incorrect magnitudes that I estimated, they were majoritively correct. My estimations for each constellation on average were correct within 0.5 of the actual magnitude which I think concludes my observation a success. Those that were not correct were due to the limitations of my own judgement as there were no measured technique involved in determining the magnitudes and colours; only what I thought after looking at them relative to other stars. My accuracy could be improved through the use of equipment which would help to magnify the stars such as a telescope. This would make the comparisons easier and allow for better (and more precise) analysis.
The location of my observation also imposed limitations on the quality of my photography. I attempted to eliminate the ‘Skyglow’, caused by streetlamps and surrounding houses, from my work during adjustments in Photoshop. However, the light pollution did have a slight effect on my accuracy which can be seen in the incorrect colour estimates. The presence of trees and my house created a problem but not significantly; the photographing of Cassiopeia required me to adjust my position as a large garden tree was blocking my view. Both of these problems could have been avoided through travelling to a more rural area with little to no light pollution as well as physical obstructions. The problem of sky glow could have also been slightly reduced if I went out at a later time when most of my neighbours would have their lights turned off, but this is no guarantee. Sky glow is damaging to astrophotography as is creates a slight orange haze on photographs especially with ones taken using long exposure – my camera only allowed 8 seconds exposure which luckily only created a very small amount of haze which I could remove using Photoshop.
Another method of improvement would be to use a better camera with better/more suited setting to clearly photograph the night sky. A better camera would have allowed me to experiment with a wider range of setting such as ISO, Aperture, shutter speed and exposure, thus allowing me to take optimum photographs of each of the constellations.
Taking more photographs on a wider range of dates would have also given me a better chance of getting better photographs. The higher the amount of repeats the more accurate, precise and reliable your readings become. Instead of going out on three dates that were consecutive days, I could have gone out on days that were reasonably spread out which would give me a more accurate result through the calculation of an average. Many of the stars I observed were variable stars meaning their magnitude fluctuates due to either swelling or shrinking of the star or the eclipsing of its light due to it being locked in orbit with another star. Therefore, more readings and an average would have given me a more valid result.
Despite the few inaccurate readings and possible improvements to my observation, I would say that the observation was a success and was designed/performed well with the resources I have available to me.
Bibliography
1
2
3
4
5
6
7
8
9
10
11
12
13