Observation of the Rotational Period of Sun Spots

A paper by
Andre James Clayden
of the
Springbrook Research Observatory

Introduction

In this project, a safe method to observe the sun is described. Photographs and sketches of sunspots were used to calculate the rotational period at latitude. The life expectancy of individual sunspot groups and singular sunspots were estimated, and their development charted.

Aims

· To measure the rotational period at latitude.

· To determine approximate life expectancy of an individual spot.

· To show how to calculate the rotational period at latitude.

· To examine and define the classifications of sunspots groups.

· To demonstrate a safe way to observe the sunspots.

· To document observations.

· To photograph and sketch sunspot groups,

· To show development of sunspots in an animated gif.

Materials used

Safety is the most important issue when observing the sun. In this project, a solar filter was used to block out the sun’s energy to protect both eyes and equipment. In addition, the sun was observed with a hydrogen alpha filter, which allowed viewing of the solar flares (Fig 1) and the surface make up.

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A hydrogen alpha view of the sun’s limb during a solar flare explosion.


Thousand oak solar filler	H Alpha filler	C14

4.5’’ Refractor	CCD video Camera	Video recorder

25mm eye piece 12mm redical 60 deg 50mm eye piece	Drafting table	Protractor

Method

1. Fit the solar filter on the 4.5’’ refractor and the H Alpha filter on the C14 before observing to make sure that all spotting scope cameras are covered to prevent any damage to equipment, or injury to any person in the Observatory.

2. Turn on the mount and point the telescope towards the sun. Using a solar filter over the finder scope the sun can be targeted with accuracy without injury to the eye.

3. Once the telescope is pointing at the sun, focus both telescopes.

4. Determine the suns north/ south Pole with the use of an eye piece with cross hairs, and orientate the eye piece so it follows RA1, which will enable determination of the axis tilt. The B2 will change throughout the year

5. Orientate the sketchbook with latitude and longitude lines already drawn on them. These can be downloaded from the web

6. Note time and date of the observation into percentage of day eg: 274 day 47.7916 is equal to 1^st of October at 011.30 and sketch in the sun spots using the 25mm eye piece with cross hairs. This will help position the spot on the sketchbook.

1 RA right ascension Part of the equatorial co-ordinate system used to specify the location of the an object in the sky.(24hrs=360degrees)

2 Bo

7. Convert the month into days. See Fig. 1

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Convert time into percentage as shown below

Example 011.00 *100 = 45.833

24 hours

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8. Note that some sunspots are just dots, while some have a ring around them. This is called the penumbra and the umbrella. These should be shaded in lightly around the sunspot.

9. Use the C14 to look at the configuration of the sunspot group. The number of sunspots in a group, and the formation of the penumbra will help determine the classification of the sunspots.

10. Fig 2 shows a number of sunspots in a group, and the surrounding penumbra.

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Fig 2 Classification and sunspot numbers within the group.

11. Take Photographs with a CCD video camera to assist with accuracy.

12. Set the drawings on the drafting table, place them in a straight line with the latitude lines matching, and find the center of each individual drawing.

13. Draw a line from the centre point of the drawing out to the central point of the sunspot. Measure the angle with a protractor (see Fig 3). This will be the starting point to measure the rotational period of this particular sunspot. Note the latitude of the sunspot.

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Fig 3. A sketch of a day’s sunspots and measurement of the angles

4. Use the www.spaceweather.com to name the groups.

5. Repeat the process every day, weather permitting.

6. When the sunspot is close to the edge of the sun (the area called the limb), take a final angle of the sunspot.

1. Calculate the angular distance that the sunspot has traveled. This is done by placing the protractor’s central point in the middle of drawing, orientating the zero line through the sunspot-starting angle to measure the final angle. Some sunspots that travel along the equatorial region will travel a greater distance than those at higher latitude, but note that the higher latitude sunspots will have a longer rotational period.

2. Calculate the angular distance traveled, and the time and date of start and finish, by using the method below

3. Work out the number of days elapsed by subtraction e.g.:

Name of sunspot group 9624

Class

Finishing time 272.645833

Start time 260.33333

Elapsed time 12.312533 days

Angle distance traveled =180deg/360deg =2

2*12.312533 = 24.625066

Rounding of =24.6 days rotational period at 0 deg latitude

Fig 4 Classification of sunspot

Class	Description	Example
A	A small spot, or spot group with no surrounding penumbra
B	Similar to A, but spots showing definite association with one another, or are symmetrically patterned (bipolar), but with no surrounding penumbra
C	A bipolar group in which the largest members are surrounded by one penumbra
D	A bipolar group in which major spots exhibit a penumbra.
E	Very large bipolar group, larger than 10 degrees across; the major spots exhibit very complex penumbra, between which are smaller spots many of which (or all) exhibit penumbra
F	The largest bipolar groups, 15 degrees or larger, normally surrounded by complex penumbra and still showing random small spots
G	Similar to F but having no random spots
H	A large spot surrounded by penumbra with small random spots nearby; larger than 2.5 degrees
J	A single spot (polar) with a penumbra

The Zurich/Wolf number (RSN)

R S Wolf proposed that the sunspot number (n) and groups (g) be combined in such a way that the groups represent 10 times (10*)

RSN=(g*10)+n

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Fig 4

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Two different classes of sunspots and number of spots

Table 2

Date	RSN
14/9/01 257 days 47.7916	57
16/9/01 259 days 45.83	66
17/9/01 260 days 33.333	88
18/9/01 261 days 47.7916	56
19/9/01 262 days 43.75	81
20/9/01 263 days 41.6	85
21/9/01 264 days 41.6	105
22/9/01 265 days 43.75	95
23/9/01 266 days 33.333	121
24/9/01 267 days 41.6	107
25/9/01 268 days 47.7196	136
27/9/01 270 days 43.75	94
28/9/01 271 days 45.83	118
29/9/01 272 days 64.5833	98
30/9/01 273 days 47.7196	84
1/10/01 274 days 47.7196	83
2/10/01 275 days 66.6	73
3/10/01 276 days 33.33	112
5/10/01 278 days 33.333	95
6/10/01 279 days 33.333	80

25 days of observations of number sunspots represented as a RSN below

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Greenwich mean sidereal time at 0hrs UT

First convert Local time and date in to UT

Example 010.00 –10hrs = 08.00

A) Find LMST3 at 010.00 hours Springbrook Queenland time on September 21st 2001

B) 010.00 AEST5 = 08.00 UT

C) GMST4 for September 0 is 22.6161 Hours

D) GMST = 22.6161 + (0.06571* 21)+ (1.00274 * 0.800) =32.01792

E) Springbrook longitude is 153.15 which is 10.21 hours this was achieved by dividing the longitude by 15

F) LMST = 32.01792 + 10.21 = 42.22792

G) Subtract from or add to this multiples of 24 until it is in the range of 0 to 24

H) 42.22792 –24 = 18.22792 or

The method to find synodic period as below

         1                              1                            1
____________       ______________       _____________

Sidereal period = synodic period + earths period

1 1 1
___________ ___________ _________

Sidereal period = 27.5740307 + 365.25

Sidereal period = 0.036266007 + 0.0027373785

Sidereal period = 25.6

3 Lmst Local mean sidereal time

5Aest Australian Eastern Time

4 Gmst Greenwich mean sidereal time

Error of angles on 9616

Fig 5

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Sunspot Group 9616 at latitude of-15 over 9.93 days traveled 130 deg with a rotational Synodic period of 27.5 days.

Results

Fig 6

25 days of observations of sunspot group by class and number of sunspots in the group

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This animated gif will show the rotation of sunspot over 25 days. Click on file to reveal motion of sun.

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7 Sidereal period
A method of keeping which uses the motion of the stars rather than the sun.
One sidereal day is equal to 23hrs 56m4s of normal solar time.

Fig 8. Observations of a number of sunspot classes.

Sunspot groups and individual sunspots change in the course of a rotational period. Table 5 shows the changing classification and the number of sunspots within the group.

chart8.gif (4649 bytes)
Sunspot that completed a rotational period greater than one period.

Conclusions

1.    The rotation period of the sun can vary at latitude from 0 degrees.
The rotational period is 25 days.
At 35 deg latitude the rotational period is 31 days.

2.    It was noted that large sunspots at the limb cause solar flares, which was observed using the
H alpha filter.

3.    Very few sunspots survive a full rotational period, in this project 9608 renamed to 9653.survived.

4.    It was also noted that sunspots had to be categorized into groups. Groups can contain a number of sunspots. It was easier to observe the group, and the changes that this group made in the course of a rotational period.

5.    The RSN number gave an average number of sunspots that were not observed, due to the telescope's capability.

6.    Sunspot groups do change in classification during a rotational period.

7.    At any given time the number of sunspots can vary from no sunspots to a large number, and during this projects duration the minimum on one day was 2 groups, and the maximum was 9 groups.

8.    Sunspots can grow from A class to F.

9.    It was observed that large sunspot groups e.g. F class last the full rotation period where A class can last only days.

10.    The more active areas on the suns surface during this observational period is + or - 5 to 10degrees latitude.

11.    Larger sunspots E to F are at higher latitude 10 to 35 + or - latitude

12.    The sun's tilt will vary throughout the year.

13.    The sidereal time of rotation is shorter than the synodic period

14.    The calculation made in this project corresponds with documented material. The degree of accuracy in transcribing the visual to drawing, good angles and accurate notes of time is necessary to achieve good results.

15.    Making accurate drawings with a sharp pencil was used to get fine detail, then an image was taken of the sunspot.

16.    Imaging the sun was made much easier using ccd video camera, which gives the choice of consecutive images.

17.    An aperture stop had to be made to cut down the amount of light entering the camera.

18.    Making quick and accurate notations keeps the telescope cool. The heat still builds up in the telescope, which hampers focusing, and photographic equipment.

19.    There are a few methods to observe the sun, one being the projection method, which involves pointing the telescope to the sun unfiltered and projecting the image onto white card. Due to heat build up, this method can cause damage to the telescope and mirrors. Another is to observe the Soho site direct from the internet.