A Field Book of the Stars Part 3

Sk.--streak-leaving meteors.

T.--train-leaving meteors.

THE CONSTELLATIONS OF SUMMER.

[Ill.u.s.tration: Maps showing the princ.i.p.al stars visible from Lat. 40 N. at 9 o'clock, July first.]

DRACO (dra-ko)--THE DRAGON. (Face North.)

LOCATION.--About 10 from a Urs Majoris--from a to d is 10--slightly south of, that is above, the line from a to Polaris, is Giansar, ? in the tip of the Dragon's tail. Above ?, and almost in line with it, are two more stars in Draco, which form with two stars in Ursa Major a quadrilateral. (See diagram.) Draco now curves sharply eastward, coiling about the Little Bear as shown, then turns abruptly southerly, ending in a characteristic and clearly defined group of four stars, forming an irregular square, representing the Dragon's head. This group is almost overhead in the early evening in summer. The star in the heel of Hercules lies just south of the Dragon's head. The brilliant Vega will be seen about overhead, 12 southwest of the Dragon's head. Eltanin, one of the Dragon's eyes, is noted for its connection with the discovery of the law of aberration of light. It is of an orange hue, while the star , near it, is white. Note Thuban, once the Pole Star, at one corner of a quadrilateral that Draco forms with Ursa Major.

Thuban could be seen by day or night from the bottom of the central pa.s.sage of several of the Pyramids in Egypt.

The rising of Eltanin was visible about thirty-five hundred years B.C.

through the central pa.s.sages of the temples of Hathor at Denderah. The Egyptians called Draco "The Hippopotamus."

Vega and the four stars in the Dragon's head offer an opportunity to compare the first five stellar magnitudes with which all should be familiar.

[Ill.u.s.tration: DRACO]

LYRA (li-ra)--THE LYRE.

LOCATION.--Lyra may be easily distinguished because of the brilliant Vega, its brightest star, which is situated about 12 southwest of the Dragon's head. It is unmistakable, as it is the brightest star in this region of the heavens, and the third brightest in this lat.i.tude. In July and August Vega is close to the zenith in the early evening.

The six bright stars in Lyra form an equilateral triangle on one corner of a rhomboid. A very characteristic figure.

e is a pretty double for an opera-gla.s.s, and a 3" gla.s.s reveals the duplicity of each star of this pair. e is therefore a double double.

? is a double for a good gla.s.s.

is a variable, changing from magnitude 3.4 to 4.4 in twelve days. At its brightest it is about equal to its near neighbor ? Lyr.

The noted ring nebula lies between and ?. A 3" gla.s.s reveals it but a powerful telescope is required to render its details visible.

If the distance from the earth to the sun equalled one inch, the distance from the earth to Vega would be 158 miles.

Vega was the first star to be photographed, in 1850. It is visible at some hour every clear night, and has been called the arc-light of the sky. Its light has the bluish-white hue that suggests "a diamond in the sky."

The spectroscope reveals that Vega is a star probably only in its infancy, as hydrogen is its predominating element.

[Ill.u.s.tration: LYRA]

CYGNUS (sig-nus)--THE SWAN, OR THE NORTHERN CROSS.

LOCATION.--Deneb, the brightest star in Cygnus, is at the top of the cross, and a little over 20 east of Vega. It forms a triangle with Vega and Altair in Aquila--Altair being at the apex, about 35 from Deneb and Vega.

Cygni is at the base of the cross, and a line drawn from Vega to Altair nearly touches it. It is a beautiful colored double for a small telescope.

Note "61," one of the nearest stars to us. It was the first star whose distance was measured (by Bessel in 1838). It is a double star and 10.4 light years distant.

The cross is nearly perfect and easily traced out. It lies almost wholly in the Milky Way.

Note "The Coal Sack," one of the dark gap in the Milky Way.

Cygnus contains an unusual number of deeply colored stars and variable stars.

? Cygni has a sixth-magnitude companion, and ? is in the midst of a beautiful stream of faint stars.

This region is perhaps richer than any similar extent in the heavens.

An opera-gla.s.s will reveal many of its beauties.

Herschel counted 331,000 stars in an area of only 5 in Cygnus.

[Ill.u.s.tration: CYGNUS]

AQUILA (ak-wi-l)--THE EAGLE, AND ANTINOS. (Face Southeast.)

LOCATION.--Half-way up the sky in the Milky Way, you will see three stars in a line, the middle one much brighter than the other two. This bright star is Altair, in Aquila. It forms with Vega and Deneb an isosceles triangle. Altair is at the apex, about 35 from the other two. A triangle is formed by Vega, Altair, and Ras Alhague, in the Serpent Bearer, which is about 30 west of Altair.

This is a double constellation composed of Aquila and Antinos. Altair is in the neck of the Eagle, Alschain in the head of Antinos.

When the moon is absent, a rude arrowhead can be traced out, embracing almost all the stars in Aquila.

? is an interesting variable star, changing from magnitude 3.5 to 4.7 and back again within a period of 7 days 4 hours 12 minutes.

Altair rises about 8 north of the exact eastern point on the horizon.

In A.D. 389 a wonderful temporary star flashed out near Altair that equalled Venus in brightness and vanished within three weeks' time.

[Ill.u.s.tration: AQUILA