lab 11

1 Name: ______________________________ Partners: ____________________________ ____________________________ AST 111 Lab #11 Solar Activity Objectives • To measure, graph and analyze the heliocentric longitudes and latitudes of sunspots over time • To estimate the rate of rotation of the Sun • To plot the numbers of sunspots over the past several decades and the past four centuries • To examine other active phenomena on the Sun References • Annual sunspot count data is available from the National Geophysical Data Center (NGDC) through https://www.ngdc.noaa.gov/stp/space-weather/solar- data/solar-indices/sunspot-numbers/american/tables/ • Decadal sunspot count data derived from http://www.sws.bom.gov.au/Educational/2/3/6 • Images of the Sun available from Big Bear Observatory through http://www.bbso.njit.edu/ Materials • Colored pens &/or pencils • Soft plastic/rubber ruler • Protractor Introduction Many objects in the solar system rotate independently on their axes, like the Earth. Does the Sun rotate? And how can we tell? The Sun’s surface (the photosphere ) is exceedingly bright, but on occasion the disk of the Sun can show dark “spots”. Sunspots have probably been observed for millennia, but it was Galileo who showed that they are features of the Sun itself. Moreover, he also noted that sunspots move across the disk of the Sun, allowing astronomers to measure the Sun’s rotational period. Solid objects such as the Earth rotate uniformly; that is, every point on the Earth’s surface rotates with the same period. Gaseous objects such as the Sun, however, are not so constrained. Different latitudes are free to move independently of each other, and thus the Sun can show differential rotation , where the period of rotation may differ according

2 to latitude. We will examine the rotation of the Sun via observations of sunspots, and then consider the number of sunspots seen from year to year and decade to decade. Sunspots are regions on the surface of the Sun that are created by intense magnetic fields. They appear dark on the face of the Sun because they are cooler than their surroundings; in actuality, they are very hot (T = 4000 K) by Earth standards. Individual sunspots may last for weeks before disappearing. Sunspots are observed at the photosphere and follow the local rotational period of the Sun. The Sun has two rotational periods, the synodic period and the sidereal period. The sidereal period is the “real” rotational period of the Sun, but beca use the Earth orbits the Sun, we see a combination of those two motions, which is the synodic period. The sidereal period of the Sun may be calculated from the Sun’s synodic period and the Earth’s orbital period about the Sun: Y S P 1 1 1 + = where S is the synodic period of the Sun, Y is the Earth’s orbital period (365.2422 days), and P is the sidereal period of the Sun. Careful determination of S thus allows us to determine P . Part #1: The Period of Rotation of the Sun Use the printed images provided or refer to the image file. If you are taking measurements off a computer, a rubber or soft plastic ruler is best so as not to scratch the screen. You will be taking measurements of sunspots from these images. Before starting, pick a sunspot that will show up on several (at least 5) consecutive images. Note that spots can be dark or bright due to the type of filter being used to observe the Sun. Refer to Figure 11-1 during the following instructions. 1. Draw crosshairs (a straight horizontal line and a straight vertical line) across the middle of the Sun. 2. Draw a straight horizontal line through the sunspot. Measure its distance from the vertical line (crosshair). This number will be negative if to the left (East) and positive if to the right (West). Distance from center = __________ cm 3. Measure the distance from the vertical crosshair to the edge (limb) of the Sun along the sunspot ’ s line. Record this result below: Distance from center to limb through sunspot = ________ 2am B. 5cm

4 Table 11-1. Observations of a Sunspot. Date Distance from Heliocentric Heliocentric Center (cm) Longitude (°) Latitude (°) ______ __________ __________ __________ ______ __________ __________ __________ ______ __________ __________ __________ ______ __________ __________ __________ ______ __________ __________ __________ ______ __________ __________ __________ ______ __________ __________ __________ ______ __________ __________ __________ ______ __________ __________ __________ ______ __________ __________ __________ 8. Calculate the average heliocentric latitude for your spot and record it below: Average heliocentric latitude = _________ ° 9. To find the sidereal rotational period for this sunspot, we need to complete a few steps. Chances are your spot isn’t seen to cover the entire length across the Sun – either we don’t have enough images or the spot disintegrates before making the entire trip. (a) Measure the entire horizontal length across the Sun for your spot (see Figure 11-1) and record the result below: Total length across for spot = __________ cm (b) Measure the distance traveled by the easternmost (leftmost) spot to the westernmost spot (rightmost). You may need to mark one or more images. Length traveled by visible spot = __________ cm 1017 I 6.2 20 1018 - S 3.1 70 1019 2 12.4 To 10110 9.5 21.7 26 10111 4.5 27.9 26 1912 5 31 Jo 10113 6 37.2 N 10124 4.5 27.9 20 10125 3 18.6 20 cope 2 12.4 To W 13 13

5 (c) Note the number of days the spot took to travel the above distance. For example, if your spot was seen in pictures from October 10 th through October 17 th , the total days traveled would be 7. Number of days traveled = ________ days (d) Use these facts to calculate the number of days the spot would have needed to travel completely across the face of the Sun. For example, if the total length across was 11.5 cm, we saw the spot travel for 8 days, and the distance the spot was seen was 6.0 cm, then the time needed for the Sun to make the entire trip would be (7 ࠵?࠵?࠵?࠵?) ( 11.5 ࠵?࠵? 6.0 ࠵?࠵? ) = 15.3 ࠵?࠵?࠵?࠵? Using your numbers from above, show the work for your own calculation and record the result below: Total travel time = ________ days (e) Because we’re only seeing half of the Sun, double this number to get the synodic rotational period of the sunspot: Synodic period S = ________ days 10. Finally, to find the sidereal period for this sunspot, we rearrange our equation (see the introduction) to solve for t he sideral (“real”) rotational period of the Sun: Y S Y S P + u = Calculate the sidereal period and record the result below. Show your work. Sidereal period = __________ days LO co ( Ko ) = a. a 43 ? p :( 43 - 2) ( 21.6 ) - = 933.12 43.2 t 21.6 14.4

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8 Table 11-2. Mean Yearly Sunspot Activity since 1946 Year Number Year Number Year Number of Sunspots of Sunspots of Sunspots 1946 100 1981 147 2016 26 1947 171 1982 115 1948 167 1983 65 1949 174 1984 44 1950 104 1985 16 1951 64 1986 11 1952 31 1987 29 1953 13 1988 101 1954 3 1989 162 1955 35 1990 145 1956 126 1991 144 1957 168 1992 94 1958 172 1993 55 1959 145 1994 31 1960 102 1995 18 1961 45 1996 8 1962 30 1997 20 1963 22 1998 73 1964 7 1999 96 1965 12 2000 123 1966 39 2001 123 1967 86 2002 109 1968 98 2003 66 1969 105 2004 43 1970 107 2005 30 1971 67 2006 15 1972 67 2007 8 1973 37 2008 2 1974 32 2009 16 1975 14 2010 16 1976 12 2011 50 1977 26 2012 53 1978 87 2013 61 1979 146 2014 75 1980 149 2015 4

10 Table 11-3. Decade-Averaged Sunspot Counts since 1701 Decade Average # Decade Average # of Sunspots of Sunspots 1700s 21.4 1950s 94.5 1710s 30.7 1960s 60.1 1720s 54.3 1970s 66.6 1730s 53.7 1980s 83.0 1740s 37.8 1990s 65.0 1750s 35.5 2000s 39.4 1760s 57.5 1770s 69.8 1780s 71.8 1790s 28.4 1800s 26.1 1810s 22.4 1820s 32.6 1830s 66.7 1840s 57.4 1850s 45.6 1860s 53.2 1870s 40.6 1880s 35.2 1890s 45.2 1900s 36.4 1910s 41.1 1920s 41.8 1930s 54.3 1940s 73.6

11 #ofMSpo# J Z Z % So Go to Eo Eo too ' l l l l l l l l l Ino - " " Z 1740 - I 760 - i :-& 1780 - 1800 - l TE l 20 - # 1840 - . - ( 860 - i v 1880 - u 1900 - ' iii : 6 1960 - . I 1980 - . . 2000 - .

13 4. Convection brings bubbles of hot gas to the photosphere, giving the Sun a rough appearance called granulation (individual bubbles are called granules ) when seen through a telescope using a proper light filter. Which letter refers to granules? 5. The solar wind consists of high-energy particles (mostly protons) blown off the surface of the Sun and traveling at high speeds through the solar system. Which type of object above best correlates with the solar wind? 6. When would you expect to see the numbers of flares and prominences be largest – during a solar maximum (when sunspots are most common) or during a solar minimum (when sunspots are least common)? 7. The Sun’s light output is very stable for a star, but it does vary a little bit (about 0.3% of its total from solar minimum to solar maximum). (a) The Earth underwent one of its period “Little Ice Ages” in the decade of the 1810s, when winters were much colder and lasted longer than average (1816 was nicknamed “1800 and froze to death”). Were the number of sunspots far larger or far fewer than average in the 1810s? (b) When would you expect the Sun to be at its brightest (and therefore hottest) – when the Sun is at a solar maximum or a solar minimum? (c) One of the important issues of our time is global warming (a.k.a. climate change). Do geologists take solar activity into account when creating their models of climate change? B Solar flare Solar maximum far fewer Solar maximum yes