Halley in the past

Planet. Space Sci., Vol. 42, No. 8: pp. 63 I 634, 1994 Copyright c 1994 Elsevier Science Ltd Printed in Great Britain. All rights rcservcd 00324633/94 $7.00 + 0.00

Pergamon

0032-0633(94)EOO79-6

On the brightness of comet P/Halley in the past s. GajdoS Department of Astronomy and Astrophysics, 842 15 Bratislava, Slovak Republic Received 3 August

Faculty of Mathematics

and Physics, Comenius

University,

Mlynska

dolina

1,

1993; revised 29 March 1994; accepted 29 March 1994

Analysis Thirty apparitions of P/Halley were used for this analysis. Positions of the comet at the time of its perihelion passage with respect to the Sun and Earth were determined and groups of similar geometry were identified. Within these groups the observing conditions were similar, so that their periods of visibility should be comparable for a constant absolute magnitude. The only data which are suitable and available for such purposes, are apparent magnitudes of the comet, the discovery dates and the dates of the last observations, in all cases by naked eye. They conic from historical records collected by Vsekhsvyatskij (1958) and

Introduction The brightness behaviour of different periodic comets is not considered to be the same. On the contrary, during the lifetime of comets there arc various periods, which form specific evolutionary patterns. As for P/Halley, this extraordinarily bright periodic comet behaves mostly as (1) (i.e. with periods of rather stable activity persisting over tens of revolutions, with fluctuations of less than + 1 mag in the absolute brightness), with episodes of type (7) (i.e. with post-perihelion brightness surges, lasting one to two month, with magnitudes up to 5 mag) observed in 1836 (Krcsak, 1986): and again in 1991. Really, thecomct seems to display a rather stable activity. This agrees with the nearly stable nongravitational effects determined from the last seven apparitions. The aim of this paper is to search for any irregularities within the period from which observations ofP/Halley arc available, which could imply any ovcrlaping of obvious fluctuations of f I mag in the absolute brightness. This result could be useful for the study of aging of periodic comets.

0 0

Fig. 1. The position Correspondence to : s. GajdoS

Earth-Sun

of comet P:‘I-Iallcy with respect to the joint in each of-its last 30 apparitions, since 240 BC

632

3. GajdoS : Brightness of comet P/Halley in the past

r

-239

-11

11 il

684

912

Returns

of

1145

1378

1607

1635 1986

P/Halley

Fig. Z(a). Duration of naked-eye visibility ~columns) and absolute magnitude (circles) for all returns considered of comet P/Halley. Some intervals of absolute magnitude amongst values of absolute magnitudes by Vsekhsvyatskij (1958) are replaced by the mean value with error bars

0

0

C

0 ii

c

3,

-239

-11

I,,

I

2%

I

451

I

I,,

,

684

Returns

,

912

,

,

I

li4.5

f

~ 1378

1607

m 1835 1986

of P/Halley

Fig. Z(b). Duration

of naked-eye visibility (columns) and absolute ma~itude P/Halley for its returns from groups B + L

Marsden (1989). The 1986 return was added by Green and Morris (1986). The missing or incoplete data were supplemented by Gajdog (1993). Several groups (A-O) with different number of members are marked on the diagram of positions of perihelia at individual returns P/Halley (Fig. 1). There are some groups with very similar geometrical conditions. Unfortunately, in most of these cases only limited reliable data are available, in particular as to the absolute magnitudes. Statistically more significant are numerous groups, although on a longer arc, such as groups B, F, I, L. Most significant was a combination of pairs of groups in reverse (mirror) positions : combinations of groups B + L and F + I, respectively. Three similar diagrams are presented :

(circles) of comet

for all 30 returns (Fig. 2a), for groups B+L (Fig. 2b), and, finally, for groups F + I (Fig. 2~). These three groups (total, B+L, F+I) were analysed with respect to the duration of visibility both in pre-perihelion and post-perihelion periods. The results are shown in Fig. 3a-c.

Discussion The completion of the data on the absolute magnitudes and duration of visibility by naked eye, and construction of some diagrams comparing similar passages of P/Halley

633

s. GajdoB : Brightness of comet P/Halley in the past I

1.I

912

6

Returns

1145

1378

1607

1835 1906

of P/Halley

of naked-eye visibility (columns) and absolute magnitude (circles) of comet P/Halley for its returns from groups F + I

Fig. 2(c). Duration

during its last 30 returns are the main results of this paper. Four relatively numerous groups were selected for this. As expected, exact conclusions cannot be made from these diagrams, but on the basis of their careful analysis more complete information becomes available. 1. There are some indications that the brightness behaviour of P/Halley in the past is impossible to explain by a progressive fading. It seems that the brightness decrease of the comet was irregular. The set of diagrams suggests

some brightness increase of the comet within five apparitions of the comet (Fig. 2a,b) in 912-1222. This conclusion cannot be affected by low values of both the absolute magnitudes and durations of visibility in 989 and 1222. Although the period of visibility was according to Marsden (1989) and GajdoS (1993) substantially longer (about three times), we must rely on the historical data, which record the last observations seven days after the perihelion passage, when geometrical conditions were still

T

T I I I I I I

I

I

I

I

I

I

I

I I1 1986

I

I

I

t

,

t

ll,ll,,i,Il

_____

1910

I835

‘I

___

_______

1910

_

1835

1759 1682

1607

1607 1531 74%

1378 1301

1378 1301 1222

__----_._---_-_-_-_-__,,45

1145 1066 989 912 837 760 684

607

t

530

451 374 -

295

_____

218 -

218

142 66 -11 --86 -163 1"

1

60

40

'

1

'

20 (-)

pre-perihelion

I

I

(+f 20

I

I

-239 II 1

ii

I

40

60

80

loo

T (days) post- perihelion

Fig. 3(a). Duration of naked-eye visibility of comet P/Halley (in horizontal scale) for its all apparitions (in vertical scale) with respect to perihelion

;I.:,&;_;_;-i_v9, 60

40

20 t-j

pre-perihelion

,

(+) 20 40 60 80 T (days) post- perihelion

,

,

,

loo

Fig. 3(h). Duration of naked-eye visibility of comet P/Halley for its apparitions from groups B (solid lines) and L (dashed lines) with respect to perihelion

$. GajdoS : Brightness of comet P/Halley in the past

634 T I

I

I

,

,

I

I

I

I

I

I

I

I

I,

II

I

1682 _---_

___ ,531 _______..e 1456

1222

684 530

__----_--_-__-‘pj,

of visibility was limited by unfavourable geometrical conditions, as seen from the Earth. It must be noted that in Vsechsvyatskij (1958) the value of absolute magnitude is missing for that return. Very similar values of the duration of visibility appear in the other passages of group E. 2. Conclusions from the preceding paragraph would not apply if we would not insist on the old original records, very incomplete or absolutely insufficient. If so, the brightness increase of P/Halley within the above mentioned period could be due to an increasing degree of completeness of the historical sources. 3. The last four apparitions indicate a decrease of the absolute magnitude, except of 1986. At the same time, there are much longer periods of naked eye visibility due to many more observers with ephemerides available. 4. The diagrams of pre-perihelion and post-perihelion visibility of the comet (Fig. 3a-c) illustrate, as expected, the differences in the geometry of the individual returns. The effect is more significant in Fig. 3(b) (except 218) than in Fig. 3(c).

-11 -__-------m--86

II

’

1 1 1

1 f

60

40

20 (-)

pre-perihelion

I

I

(+) 20

I

I

40

I

I

60

I

I

80

I

II

IO0

T (days) post- perihelion

Fig. 3(c). Duration of naked-eye visibility of comet P/Halley for its apparitions from groups F (solid lines) and I (dashed lines) with respect to perihelion

suitable for observation. It seems that Vsekhsvyatskij (1958) derived his low absolute magnitude from the same source. The value differs substantially from the neighbouring ones. According to the tables of Selegnikov (1970) the Moon cannot have affected the dates of the last observations in these cases. It seems that the brightness increase during the period 9 12-1222 ended in 1222. For this apparition the situation was different. In this case the duration

References Gajdol, s., Geometrical conditions of individual returns of comet P/H&y, in Meteoroids and Their Parent Bodies (edited by J. Stahl and I. P. Williams), pp. 105-108. Bratislava, 1993. Green, D. W. E. and Morris, C. S., The visual brightness behaviour of P/Halley during 1981-1986. Proc. 20th ESLAB Symposium on the Exploration of Halley’s Comet, Heidelberg, ESA ;P-250, pp. 613418, 1986. Kreshk, L., On the aging process of periodic comets. Proc. 20th ESLAB

Symposium on the Exploration of Halley’s Comet,

Heidelberg, ESA SP-250, pp. 433-438, (1986). Marsden, B. G., ~atalogue of Cometary Orbits. Smithsonian Astrophysical Observatory, Cambridge, MA, (1989). Selehikov, S. I., Zstorija kalendarju i khronoiogija. Izdatel’stvo Nauka, Moskva, 1970. Vsekhsvyatskij, S. K., Fizicheskije kharakteristiky komet. Gos. izdatel’stvo fiz.- mat. literatury, Moskva, 1958.