Observing Project Assessment - 20% of total

As part of PHY241, you will be expected to complete a simple observing project using the 16-inch telescope on the roof of the Hicks Building. We will use photometry of a Galactic open cluster to determine the age and distance of the stars in the cluster. This project is designed to give you basic hands-on experience of astronomical observing and data reduction, and can be completed in a few hours of telescope time. The observing must be done in groups of up to 4 students. You must sign up to a group on Blackboard by the end of week 1 Friday 29 September 2023. If you do not, I will assign people into groups at random.

There are three aspects to the observing project.


Well before your scheduled observing run, you choose which open cluster to observe. You will find the specifications of the Hicks Observatory useful in your planning and when writing your report. You will need to include a section on your planning in the final report. This section must contain a calculation of the transit time and the transit altitude of your chosen object. You may find the positional astronomy notes from PHY127 of use.

A suitable open cluster must be:

  • old enough so that some stars have turned off the main sequence;
  • close by, so that the stars that have turned off the main sequence are bright enough to observe with the 16-inch telescope from Sheffield;
  • small enough in angular size to fit within the field of view of the 16-inch telescope with the focal reducer;
  • visible from Sheffield in the months of October and November.

I give more detail about these points below.


You may find this link useful about main sequence lifetimes.


This course will teach you the skills you would need to put a quantitative number on this, but for now, just know that you want the stars at the main sequence turn off point to have a V-band brightness of V < 13 to 14.

Note that you will often see the integrated magnitude of all the stars given for the cluster. This is how bright the cluster would appear if you couldn't resolve individual stars - you don't want to use this magnitude to make decisions about the brightness of stars at the main sequence turn-off!


You can find the field-of-view of the Hicks observatory in the specifications. The cluster should fit within this.

A list of potentially suitable open clusters are listed below; select one from this list before you observe, and email Stuart Littlefair and Paul Kerry to inform them of your group number and cluster choice. If you wish to observe a different open cluster, that is fine, as long as it meets the criteria above.

NGC 7789

  • \(\alpha\) = 23:57:24
  • \(\delta\) = +56:42:30
  • Turn off @ \(V \sim 13\)
  • \( D \sim 16' \)


  • \(\alpha\) = 08:51:18
  • \(\delta\) = +11:48:00
  • Turn off @ \(V \sim 12\)
  • \( D \sim 20' \)

NGC 6939

  • \(\alpha\) = 20:31:30
  • \(\delta\) = +60:39:42
  • Turn off @ \(V \sim 13\)
  • \( D \sim 7' \)

NGC 2627

  • \(\alpha\) = 08:37:15
  • \(\delta\) = -29:57:18
  • Turn off @ \(V \sim 12\)
  • \( D \sim 10' \)

Your observing session will take place in person on the roof of the Hicks Building. It must be completed in a specified period: Mon 09 October - Friday, 10 November 2023 (weeks 3-7), although please note that observing is not possible over weekends and there may be short periods when either myself or Paul Kerry is unavailable.

Sign-up is done using the online sign-up sheet; there is a link to this on Blackboard. Paul Kerry or myself will contact you in advance if observing will be carried out; please read the full instructions on how observing works (you can find this on Blackboard). Although you should be able to complete all your observations in a single session, to allow for the vagaries of British weather we expect you to sign up for at least two evenings per week until you have successfully completed your observing. If you cannot do this, you must discuss the problem with me or Paul Kerry before the start of the designated observing period, or as soon as the problem (e.g. illness) becomes apparent. Note that reading week is not a holiday. We expect you to sign up during reading week as usual.

Attendance at the observing is compulsory - you will not receive any marks for the project if you fail to show up or if you have not made every effort to sign up for regular time slots. Note that, unless previously agreed with me or Paul Kerry, if you are unable to attend a successful observing session with the other members of your group, it will not be possible for you to observe at a later date on your own. Note also that no resit of the observing project is possible unless you have observed, so missing it will make it much more difficult to pass the module.

We strongly advise signing up for observing as soon as possible: students who fail this module tend to be those who leave signing up until the last minute and then suffer from poor weather at the end of the observing period. This is no excuse, as there are usually clear periods at the start of the observing period which no students sign up for. Only if the entire period is unusable, or if you have genuinely serious reasons as to why you could not do the observations (which in most cases must be supported by documentary evidence), will this component not count towards the final mark.

Data Reduction and Report

After you have obtained your observations, we will work through the data reduction and analysis during the PHY241 computer labs. Note that this element of the project, and the subsequent write-up, must be your own work - do not work in your observing groups.

Your write-up should be similar to a formal laboratory report. There must be sections describing the planning stage, the observations (a description of the equipment used, the observing conditions and the data that was taken), the data reduction and the data analysis. You will be penalised if you omit an analysis of the errors, and if you fail to compare your results with literature values. Some advice on how to write the report is here, and the rubric used to mark the report is here. I strongly recommend peer marking each other's reports with this advice and rubric in mind.

You may well want to prepare your reports using the Jupyter notebook - it is possible to produce PDF documents from the notebook. Please submit electronic copies on Blackboard: the deadline is Friday 15th December 2023 (16:00). Note that this deadline is the final week of term, and has been set to make the observing window as long as possible. However, you will undoubtedly have other pieces of work to hand in around this time, so it is in your interests to complete your observing and hand in your report as early as possible in the semester.