ASTRONOMICAL NOTES FOR JUNE.

Star (Christchurch), Issue 8943, 31 May 1907, Page 1

ASTRONOMICAL NOTES FOR JUNE.

The sun comes to its northern solstice on June 23 at 1.53 a.m. The word solstice translated literaUy means the stationary point of the sun, and is a term that has been used by astronomers since the primitive days, when the length of a shadow was measured to determine tjhe progress of the year. At the beginning of June the sun's daily motion in declination is eight minutes, which makes each day in these latitudes eighty seconds shorter than the previous day. But the motion becomes •slower as the solstice is approached., so that on June 21 it only ajnounts to forty seconds of arc, making a difference of seven seconds of time in the length of the day. The same may be said of the southward motion after the shortest day. At first the sun mov«s very slowly in declination, but his motion becomes more rapid daily. It is quickest at the time of the equinoxes, when it amounts to twenty-three minutes of are, making the length of the day alter three minutes of time daily. On June 6 the- earth will be moving directly towards the planet Mains, so that ime planet will appear to be stationary in right ascension. After that the earth will be overtaking and passing the pLanet, so that for some tune Mars will appear to move retrograde. All this time he will ,be moving in declination, at first to the south and cftenyaircjs ttrtihe north, "a t. a his""Ht> 4r ~- parent path marked o>n a map can only be described by compaaing it to & rather broad number 6. It must be remembered that on star maps the right hand side is tSfoe w«?«st. The second magnitude star, Sigma Sagitarii is in the upper part of the. 6, and tihe fourth magnitude, Tail Sagitarii is within the enclosed space. Consequently Mars circles round the smaller star, and crosses his own. path again on September 22 at tibe same place which be occupies on June 13. On April 28 Mars was at tfoe top of the 6. He was then in conjunction with Sigma Sagitarii and 2deg 29min north of it. On July 15 his retrograde motiotn again brings him into con junction with this star, but he is tlhen at the bottom of th© 6 and passes 2d«g 9min south of the star. The tiikd conjunction is on September 2, when he is at the top of the enclosed space, and is then only 1 deg llmin south of the star. Retrograde motions suoh as these are seen at the opposition of a/ny planet, but they are most conspicuous in the case of Mars, because the proper motion of Marts is faster than that of any other exterior planet, so that it takes longer for the earth to overtake him. The retrograde motion is fastest at the time of the opposition, wiben Mars and the earth are alongside one another and moving in nearly the same direction. Jupiter will eoon be in conjunction with tihe sun, and, consequently, ho sete soon after the sun. The Nautical Almanac does not give the phenomena of the satellites from June 17 to August 14, because during that time tihe planet is too near the sun for the satellites to be seen. On June 12 there is a very close conjunction of Jupiter witHi the moon. In the couth of New Zealand the planet will be occulted by the moon, but at Christchurch there will be a space of about two minutes between them. The time of nearest approach is 6.17 p.m., and the moon sets three minutes later. On the evening of June 16 Jupiter and Mercury will be in conjunction, Mercury being ldeg 41min north. Mercury may also be isecn on June 11 in close conjunction with the star Epsilon Geminorum. The least distance between them is about twenty seconds, but they will set b&fore they are as close together as this. Mercury ie at his greatest eastern elongation on June ■27 , when his setting will be delayed until 6.32 p.m., the sun 'having set at 4.29 p.m. Venus and Saturn are both visible in the morning, rising about two hours before the sun. On June 26 the moon will be full, and will also be almost at her nearest to the earth and at her farthest south. These three favourable circumstances combine to produce an exceptionally brilliant moonlight night. When the moon is at her nearest to the earththat is, in perigee— her diameter is greater' than when in apogee in the ratio of eight to seven. The apparent surface is therefore increased in the ratio of sixty-four to forty-nine._ Being in declination 21 south, her altitude above the horizon is considerable, so that the apparent diameter is "augmented." Consequently some full moons give quite a quarter more light than others. The long dark evenings at the beginning of June are very favourable for the observation of star-clusters and nebula;. One of the richest portions of the Milky Way is that between Scorpio and Sagittarius, a position which is easily recognised at present as just above the planet Mars, and here any small telescope shows numbers of dense clusters of stars. The Southern Cross is at" its greatest altitude between 8 and 9 p.m. About half a degree eaet of the farthest east of the four bright stars a email fifth-magnitude star is visible. Here the telescope shows a beautiful cluster of coloured stars, sometimes called the Jewel Cluster, owing to Herschel having compared it© colours to "a superb piece of fancy jewellery." There are eight fairly . bri«k+- stare, of which two are blue, two I

red, three green, and one white, and there are more than a hundred fainter ones, some of which seem to be coloured also. Alpha Crucis, the first-magni-tude star in the Grose, is a triple star consisting of two yellow eeoond-magni-tude stars five seconds apart, and a blue sixth-magnitude star about lmin south. The following occupations of stars by the moon are calculated for Christchurch : — Dis- ReJune. appearance, appearance. 6 33 Ceti . . . 6.22 a.m. invisible. 24 B.A.C. 5579 . . 7.17 p.m. 7.49 p.m. 26 B.A.C. 6093 . . 3.2S a.m. -1.27 a.m. 26 33 Ssgitarii . . a. IS p.m. 9.16 p.m. 26 X.I. Sagitarii . . 10. 4 p.m. 10.43 p.m. 27 Pi Sagitarii . . 4. 3 a.m. 4.53 a.m. 23 B.D. 17, 6216 . 2.23 a.m. 3.23 a.m. 30 45 Aquarii . . 5. 6 a.m. 6.14 a.m.