« SebelumnyaLanjutkan »
CHART SHOWING RELATIVE BURATHON OF TWILHGHT, BAXILIGHT AND : DARKNESS FOR I.A.T. 42°--. - ** - - HOURS
Note.—Twilight is considered to last until the Sun is 18° below (vertically) the horizon, and to begin when the Sun reaches a similar point in the morning—or 18° before sunrise. When the line on which this 18° is measured is shortest then the twilight will be the shortest, and vice versa. This causes the shortest twilights to # occur in the winter months in northern latitudes, and longest in summer. - : - By an examination of the chart We find the measure of twilight, darkness and || § daylight of the 24 hours to be : 3 Jan. 1, Length of day . . . . . . . . . .8lm, 54m. June 21, Length of day . . . . . . . .15h. 34m. || - I,ength of twilight . . . . . . 1h. 45m. length of twilight. . . . 2h, 30m. || - The remainder of the space will more than make the 24 hours, which is due to H refraction of light, which causes an increase in the apparent length of the day, as || also of duration of the twilights. This apparent error is grca test in the winter || months, as the Sun then shines through 9. § onser and deeper atmospheric envelope, o A4 PLANETS IN CONJUNortex \ PH.ANETARY CONo UNCTMONS AND OTHER PIENOMENA FOR, 1906,
- # in the same direction as our line of vision, and hence they can have no apparent
horizon at 5 h. 31 m. p. m., Washington mean time.
: their greatest angular distance east or west of the sun. Planets are said to be
- situation of PLANETs-DistancES ON HORIZON. 15 |
Note.—The time for the phenomena given in the table on the preceding page is for ; the geocentric event, and as seen from the earth's surface the error may be as much as 2.1m., more of less; but the given time is near enough for all purposes and places. :
Explanatory.—The sign C, signifies conjunction, or when an imaginary line from the north star through one of two planets or bodies in the same quarter of the heavens will also pass through the other one.
In the case of the moon and any other body, when the distance apart is #6° or less there is apt to be an occultation, as the moon’s apparent sermi-diameter jo is about 16”. This will be the case on December 30, when the centre of the moon and of Mars are only 4” of arc apart. This occultation will be visible every- #. where between the latitudes 32.9— and 34o-H, where these bodies are above the #
, ‘The inferior planets are said to be at “greatest elongation” when they attain “stationary” when they are in that portion of their orbit whence their motion is
motion to us. Bodies are at Perihelion when nearest the sun, and at Aphelion : when furthest from him. The sign 8 signifies opposition, or 180° east or West from #
the Sun. -
THE HoRizoN AT SEA LEvel.
Distancos of objects visible at varying elevations from one foot to one thou- f| sand feet. The elevations given are in feet.
DISTANCE FROM THE EARTH IN Ll GHT YEARS OF CER.
DEGREES OF TEMPERATURE AT WHICH CERTAIN SUB-
: 3 §: o ā;
§.E. To ty ## F;
Substances, F# 3 Substances, s' T- o
4 } H
Bromine freezes at . . . —20° — 7.6° ; Silver fuses at . . . . . . .#1,000° j 1,832°