How to start observations of variable stars with a webcamera. A short review of the characteristic constellations and methods which allow us to find stars suitable for amateur observations in the sky.

1. Where to begin the adventure with variable stars? The variable stars that are particularly suitable for observations for beginners Mateusz Bielski Editors: A. Majczyna and M. Należyty Logo design: Armella Leung, www. armella . fr .to Translated to English by Magda Zarzycka This project has been funded with support from the European Commission. This publication reflects the views only of the author, and the Commission cannot be held responsible for any use which may be made of the information contained therein.

2. The photometry of variable stars is ranked among the most difficult observations that can be done with the use of a webcam built on the basis of a CCD. Learning how to gather and process data requires patience and determination...

3. In reward for this you will get results that have not only didactic, but also scientific value in the broadest sense of the word. Therefore , teacher s can create with their students a true scientific laboratory at school!

4. Which stars should we choose for a start? The process of developing your own technique is difficult and time-consuming. To be able to observe weaker stars or those whose amplitudes are smaller, it is a good idea to practise with those that are , so to say , ‘ created ’ for photometric observations with a webcam. I n the sky you will find precisely such stars, whose observations almost without exception return results that impress laym e n or beginner s equally .

7. RZ Cas – light curve Julian Days

9. TX UMa – light curve (incomplete, only one arm, but the variability is clearly visible) Julian Days

11. U Cep – light curve

12. How to find these stars in the sky?

13. To be able to find the object of interest , it is necessary to know how to identify particular constellations and stars. This will require a few nights and some patience but what you will get in reward is a great satisfaction. A planisphere will be of great help while learning how to navigate around the sky. The easiest way to find it is on the internet (just search for ‘planisphere’ in any search engine) and buy it online (it costs around $8).

14. This is what a planisphere looks like Very simple instructions how to use it can be found at the back of the planisphere.

15. If you have a portable computer or have access to a stationary computer where you are, you can use electronic atlases of the sky. Most of them are commercial programs but you can also find freeware of this sort on the internet. Cartes Du Ciel is the most popular atlas It is available at: www.stargazing.net/astropc Electronic atlases are very helpful and allow users to print out accurate maps that help to identify variable stars and reference stars that are later used in the process of photometry.

16. The navigation in the night sky To navigate the sky quickly and effectively, it is necessary to learn first how to identify the main constellations. There are a few constellations in the sky whose main stars are very bright and whose shape is very characteristic and therefore easy to recognise.

17. Ursa Major , also called Great Bear

18. Ursa Major , also called Great Bear Mizar and Alcor

19. Cassiopeia

20. Cassiopeia

21. Andromeda

22. Andromeda M31

23. Ursa Minor , also called Little Bear

24. Ursa Minor , also called Little Bear Polaris

25. Lyra

26. Lyra Vega

27. Cygnus , also called Northern Cross, Swan

28. Cygnus , also called Northern Cross, Swan Vega Deneb Lyra

29. Cepheus

30. Cepheus Polaris Cassiopeia

31. Perseus

32. Perseus Algol

33. Hercules Difficult to find

34. Hercules Difficult to find

35. Taurus, also called Bull

36. Taurus , also called Bull Pleiades Aldebaran

37. Orion

38. Orion Aldebaran

39. Gemini, also called Twins

40. Gemini, also called Twins Pollux Castor

41. Bootes

42. Bootes Arcturus

43. Aquila

44. Aquila Altair

45. Auriga , also called Charioteer

46. Auriga , also called Charioteer Capella

47. Leo , also called Lion

48. Leo , also called Lion Regulus

49. Pegasus

50. Pegasus

51. Of course, there are far more constellations in the sky, but once we learn to find and recognise those most characteristic ones, finding the other ones with the use of a planisphere should not cause any problems. Constellations can be divided into those that are visible in the sky in winter, those that we can see in summer, and those that are present all year round.

55. When we know how to navigate across the night sky and we are equipped with printed maps (e.g. from Cartes Du Ciel), we can start searching for interesting variable stars in order to conduct photometric observations with a webcam.

56. In the case of the three stars presented before , the situation is simple because they belong to constellations that are visible all year round in the northern hemisphere. They are located in relation to one another in the following way:

57. In the case of the three stars presented before , the situation is simple because they belong to constellations that are visible all year round in the northern hemisphere. They are located in relation to one another in the following way: Polaris Ursa Major Cassiopeia Cepheus

58. The location of this set may be different depending on the season and the time of observation but the stars always remain in the same position in relation to one another. (Ursa Major is opposite to Polaris in relation to Cepheus and Cassiopeia)

61. From the suggested stars, the easiest is to find RZ Cas in the constellation of Cassiopeia. Find Cassiopeia in the sky. The easiest way to do this, is to go from Polaris towards Andromeda in a straight line. Polaris μ And M31

62. When we find Cassiopeia... Find the star ι (Iota) located at the extension of the arm that ends at the star Segin. Segin ι (Iota)

63. Next, already with the help of a telescope When the ι (Iota) star is in the centre of the view field of our telescope, we can easily find RZ Cas moving towards Segin (see the arrow). Segin ι (Iota) RZ Cas

64. It is best to have the variable star at the centre of the view field (the net of crosses in the telescope) and choose one of the four stars in the characteristic zigzag as the star of reference. Another variable star, SU Cas, will be in your field of view as well. It is not suitable for a star of reference, however! ι (Jota) RZ Cas SU Cas

65. It is somewhat more difficult to find TX UMa. It is in Ursa Major and we should begin with finding this constellation. Finding the constellation does not pose any problem even to beginners. Following the straight line connecting two stars in Ursa Minor: Zeta Ursae Minoris and Beta Ursae Minoris (see picture) you will find Mizar.

66. Mizar is the most popular star in Ursa Major thanks to its neighbour – Alcor, visible with the naked eye. Mizar

67. Find Phecda in the constellation. Moving from Megrez through Phecda find the star  (see the arrow). Phecda Megrez 

68. Moving still further from the bear from the χ star you will find the ψ and  stars. In a dark sky they are visible with the naked eye but it is a good idea to use a finderscope. These two stars form a triangle with the star HIP 52469.  ψ  HIP 52469

69. TX UMa is situated a little below the line that connects the stars  and HIP 52469, around 1/5 way from HIP 52469. It is not visible with the naked eye. One of the stars in the yellow circles can be used as a star of reference.  HIP 52469 HIP 52831 HIP 52881 HIP 52702 HIP 53160

70. Finally U Cep Let’s begin with finding the constellation of Cepheus, where the star is situated.

71. It will be easiest to begin with locating the star Alrai. Moving in a straight line from Polaris towards Cassiopeia, and more precisely from the star Caph, we will find the bright star Alrai, belonging to the constellation of Cepheus. Polaris Caph Alrai ι (Iota)

72. When we have found Alrai... Moving along the straight line connecting Cephei and Alrai, further from Alrai towards Polaris , we will find HIP 760. It is not visible with the naked eye, so in this step we will need a finderscope. Alrai HIP 760

73. Next, moving along the line that connects Alrai and HIP 760 in the same direction as previously, we will find U Cep. U Cep is situated more or less at the same distance from HIP 760 that HIP 760 is from Alrai. U Cep HIP 760 Alrai

74. One of the stars in the yellow circles can be used as a star of reference. HIP 5108 HIP 4966 TYC 4505-387-1 TYC 4505-558-1 HIP 3132

75. In this way we have found the stars and we can begin photometric observations. Their result will probably impress not only us, but also other students and our friends. Also the acquired skills of navigating in the sky will be a source of satisfaction and will raise admiration .