Encyclopedia of Astronomy by Patrick Moore (editor)

Author:Patrick Moore (editor)
Language: eng
Format: epub
Published: 2011-01-13T08:26:09.421000+00:00

L AST ENCY PHI fin 11/4/02 6:41 pm Page 224

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the galactic equator to the galactic poles. Heliocentric LEO (GEN. LEONIS, ABBR. LEO)

latitude is the same as celestial latitude, but corrected for a hypothetical observer located at the centre of the Sun, while heliographic latitude is measured on the Sun’s Large, distinctive northern constellation and one of the signs of the zodiac. It represents the Nemean lion killed by Hercules as the first of his twelve disk, north or south of its equator.

labours in Greek mythology, and lies between Cancer and Virgo. Leo is easily recognized by the asterism known as the SICKLE, a reversed question mark Lauchen, Georg Joachim von See RHAETICUS

formed by six of the constellation’s brightest stars, with the brightest of all, REGULUS, mag. 1.4, at its base. ␤ Leo, DENEBOLA, marks the lion’s tail. ␥ Leo, launch window Period of time during which it is ALGEIBA, is a fine visual binary with orange and yellow components, mags. 2.5

possible to launch a particular space mission.

and 3.6, separation 4Љ.6, period about 600 years. The constellation also contains Wolf 359 (also known as CN Leo, a variable star of the UV CETI type, leap second Periodic adjustment by one second of range 11.5–17.1), the third-closest star to the Sun, just 7.8 l.y. away. Deep-sky COORDINATED UNIVERSAL TIME (UTC) to ensure that it objects in Leo include five 9th-magnitude spiral galaxies: M65 (NGC 3623), remains linked to the rotation of the Earth.

M66 (NGC 3627), M95 (NGC 3351), M96 (NGC 3368) and M105 (NGC

The braking action of the tides causes the Earth’s peri-3379), the first two and last three of which are grouped close together in the od of rotation to slow by between 1.5 and 2.0 milliseconds sky. Leo I (10th magnitude) and Leo II (12th magnitude) are a pair of dwarf per day per century. In order that time as kept by atomic spheroidal galaxies in the LOCAL GROUP, about 815,000 and 685,000 l.y. away, clocks (UTC) and that derived from observations of the respectively. The Leonid meteor shower radiates from the constellation.

stars (UT1, see UNIVERSAL TIME) do not differ by more than 0.9 seconds, an extra second is introduced to UTC at BRIGHTEST STARS

midnight on either December 31 or June 30 as required.

Name

RA

dec.

Visual

Absolute

Spectral

Distance

This has the effect of producing an accumulated dif-

h

m

º

Ј

mag.

mag.

type

(l.y.)

ference between UTC and INTERNATIONAL ATOMIC TIME

␣ Regulus

10 08

ϩ11 58

1.36

Ϫ0.5

B7

77

(TAI) of an integral number of seconds. The most recent

␥ Algeiba

10 20

ϩ19 51

2.01

Ϫ0.9

K0

126

leap seconds were inserted as follows:

␤ Denebola

11 49

ϩ14 34

2.14

1.9

A3

36

Date

TAI–UTC

␦ Zosma

11 14

ϩ20 31

2.56

1.3

A4

58

1989 December 31

ϩ25.0 sec

⑀

09 46

ϩ23 46

2.97

Ϫ1.5

G0

251

1990 December 31

ϩ26.0 sec

␪ Chertan

11 14

ϩ15 26

3.33

Ϫ0.4

A2

178

1992 June 30

ϩ27.0 sec

␨ Adhafera

10 17

ϩ23 25

3.43

Ϫ1.1

F0

260

1993 June 30

ϩ28.0 sec

␩

10 07

ϩ16 46

3.48

Ϫ5.6

A0

2138

1994 June 30

ϩ29.0 sec

1995 December 31

ϩ30.0 sec

1997 June 30

ϩ31.0 sec

L

structed a 48-inch Newtonian on a fork mounting. Then, 1998 December 31

ϩ32.0 sec

having developed the most technically exact and versatile reflecting telescopes of the age (and published the details leap year Year containing 366 instead of the usual 365

of their construction), he spent over five years in Malta, days. The CALENDAR is based on a solar year of 365.

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