THE FACE OF THE SKY FOR APRIL. 



Bv W. SHACKLETON, F.R.A.S., A.R.C.S. 



The Sun. — On the 1st the Sun rises at 5.39, and sets at 6.29; 

 on the 30th he rises at 4.37, and sets at 7,17. The equation of 

 time is negligible on the 16th and 17th, hence these are 

 convenient days for the adjustment of sundials, as only the 

 longitude correction is needed. Sun-spots may usually be 

 seen on the solar disc, but they are small, and not numerous. 

 The positions of the Sun's axis, equator, and heliographic 

 longitude of the centre of disc are shown in the following 

 table : — 



Venus :- 



On April 28th, a total eclipse of the Sun takes place. It is 

 invisible in this country ; the path of totality lies almost 

 entirely over the Pacific Ocean, no large piece of land falling 

 in the shadow, A party of observers left England in F"ebruary 

 for Vav-au, one of the islands in the Tonga or Friendly Group, 

 in Mid- Pacific, where totality lasts for about three-and-a-half 

 minutes. 



The Moon : — 



OCCULT.^TIONS. — No bright stars 

 midnight either in April or May. 



are occulted before 



THE PLANETS. 



Mercury : — 



Mercury is an evening star throughout April. The planet is 

 at greatest Easterly elongation from the Sun of 19' 42' on the 

 15th. when he sets W.N.W, about 8.55 p,m. This elongation 

 is a favourable one on account of the high declination, and 

 there should be no difficulty in seeing the planet from the 

 15th to the 25th, as he sets about two hours after the Sun. 



On May 5th, Mercury is in inferior conjunction with the 

 Sun, 



Venus is a brilliant object in the evening sUy, lo(>l<ing 

 W.N.W. after sunset. 



The planet is well placed for observation, appearing fairly 

 high above the horizon at sunset, and not setting till 9,20 p.m. 

 on April 1st, and 10.50 p,m, on May 1st, 



As seen through the telescope the planet appears gibbous, 

 0-8 of the disc being illuminated, whilst the apparent diameter 

 of the disc is 13". On account of her brightness the planet is 

 fairly easy to pick up with the naked eye before it is dark, 

 and this is the best time for making observations with the 

 telescope, for Venus is a severe test for the achromatic 

 qualities of any refractor if observed on the dark background 

 of the sky ; seen in a lighter sky the outstanding colour, in the 

 telescope, due to want of perfect achromatism, is not so 

 obtrusive, and a better view of the planet is obtained. The 

 Moon will appear near the planet on April 1st, being only 

 0" 14' to the South as illustrated in the March issue, whilst on 

 May 1st the Moon will be li to the North. 



^^\RS : — 



Mars is a morning star rising E,S,E, about 3.30 a.m., near 

 the middle of the month. He is situated first in Capricorn, then 

 in Aquarius, The planet is unfavourably placed for observa- 

 tion and since his apparent diameter is only 5" telescopic 

 observations are difficult except in large instruments. 



Jupiter : — 



Jupiter is a brilliant object in the late evening sky looking 

 South-East, The planet is in opposition to the Sun on May 

 1st, hence about this date he appears South at midnight. On 

 April 1st the planet rises at 9.20 p.m., and on May 1st at 

 7 p.m., and is visible throughout the night. The equatorial 

 diameter on the 15th is 43" -6, whilst the polar diameter is 

 2" -8 smaller; this polar flattening is a conspicuous feature of 

 Jupiter, and is readily obse-'vable in small telescopes; also the 



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