Western Elongation Research Articles

Photoelectric photometry of JV

UBV photometry of JV near greatest western elongation shows this satellite to be about one magnitude fainter than previously believed. It is observed to be very red, having a B-V color index near +1.5 mag. Unlike the Galilean satellites, JV appears to bea low-albedo object.

Photometry of Dione, Tethys, and Enceladus on the UBV system

UBV measurements of Dione, Tethys, and Enceladus were made with an area-scanning photometer on several nights during the 1972/1973 and 1973/1974 apparitions of Saturn. The observed brightness variations have been separated into two components—one a function of orbital position, the other a function of solar phase angle. Dione and Tethys are brightest near greatest eastern elongation and faintest near greatest western elongation. The reverse is true of Enceladus. Opposition surges are observed for Dione and Tethys.

Photometry of Saturn's satellites: The opposition effect of Iapetus at maximum light and the variability of Titan

We present photometry, V and ( B - V), of Iapetus at six western elongations (the phase of maximum brightness) that span a range in solar phase, α, from ≈6° to <0°.4, and we find that a substantial opposition effect, >0.12 mag ( V), is present. We make a few cautious remarks about the possible relevance of the use of this result to interpret the phase curve of Saturn's ring. We also give a few measures of Rhea and Hyperion, at α ≊ 0.3°, and more of Titan, which indicate that the latter has been anomalously bright during much of 1973 and 1974, sometimes by nearly 0.1 mag ( V).

ASPECT OF THE HEAVENS FOR JANUARY AND FEBRUARY, 1955

Mercury is at greatest eastern elongation, 18° from the sun, on January 28. During the last week of January it should be easily visible in the evening twilight just above the southwestern horizon. It reaches inferior conjunction on February 12. Venus, magnitude 4.0, reaches greatest western elongation, 47° from the sun, on January 25. At this time it is rising in the southeast about three hours before the sun.

ASPECT OF THE HEAVENS FOR SEPTEMBER AND OCTOBER, 1950

Mercury is at inferior conjunction on September 17 and at greatest western elongation, 18° from the sun, on October 2. During the last week of September and the first week of October, Mercury should be visible shortly before sunrise just above the eastern horizon. On the morning of October 6 it is in close conjunction with Saturn, passing 0° 16' south of it. Venus, magnitude 3.4, is still visible low in the east just before sunrise in September, but by the end of October it appears too close to the sun for easy observation. It passes 0° 33' south of Saturn on September 29 and 0° 15' south of Neptune on October 17. Mars, magnitude +1-2, has about the same brightness and color as Antares, passing 3 τ/2° north of that star on October 7. Jupiter, magnitude 2 . 3, is in Aquarius and is prominent in the southern sky most of the night. It ends its retrograde motion on October 24. Table I lists the transits of Jupiter's satellites and their shadows, which can be observed at convenient times on the Pacific Coast. Some transits have been included which occur before sunset on the Pacific Coast but during darkness in the eastern part of the United States. Saturn, magnitude +1.3, is in conjunction with the sun on September 15. At this time the earth passes through the plane of Saturn's rings. For the next fourteen and a half years the north side of the rings will be visible. Uranus, magnitude +6, is in Gemini, changing its position

The Night Sky in June

FULL moon occurs on June l0d. 21h. 45m., U.T., and new moon on June 260.10h.02m. The following conjunctions with the moon take place : June 3d. 04h., Saturn 3°S. ; June 13d. 22h., Jupiter 5° N.; June 24d l5h., Mars 4° S.; June 24d. 18h., Mercury 8°S June 27d. 21h., Venus 4° S.; June 30d. 13h., Saturn2° S. Mercury is in inferior conjunction on .June 3 and is, stationary on June 15. The planet reaches greatest western elongation on June 28, and at the end of the month rises an hour before the sun. Venus is an evening star, setting about an hour after the sun during June, and can be seen for a short time in the western sky. Mars is a morning star, rising at 3h. 10m., 2h. 40m., arid 2h. 12m., at the beginning, middle and end of the month, respectively, and is visible for a short time in the eastern sky. Jupiter is visible in the early morning hours, Arising at 23h. 30m., 22h. 33m., and 21h. 30m. on June 1, 15 and 30, respectively. Saturn is visible during the earlier portion of the night, setting at Oh. 40m., 23h. 45m. and 22h. 50m. at the beginning, middle and end of the month, respectively. No occultations of stars occur during June. Summer solstice commences on June 21d. 18h.

The Night Sky in September

NEW moon occurs on Sept. 3d. llh. 21m., U.T., and full moon on Sept. 18d. 09h. 43m. The following conjunctions with the moon take place : Sept. 4d. 18h., Mercury 3° S.; Sept. 6d. 22h., Mars 0·7° S.; Sept. lOd. 13h., Jupiter 4° N.; Sept. 29d. 13h., Venus 6° S.; Sept. 30d. 05h., Saturn 4° S. In addition to these conjunctions with the moon, the following conjunctions take place : Sept. 9d. 10h., Saturn in conjunction with Regulus, Saturn 0·8° N.; Sept. 20d. 16h., Mercury in conjunction with Spica, Mercury 0-2° S. Mercury sets at 19h. 15m., 18h. 45m. and 17h. 52m. at the beginning, middle and end of the month, respectively, and is too close to the sun for favourable observation. The planet reaches its greatest eastern elongation on Sept. 25. Venus is a morning star, rising at lh. 15m., lh. 30m. and lh. 55m. at the beginning, middle and end of the month, respectively ; it has a stellar magnitude of approximately – 3·8 throughout most of September, and can be observed with phase a little more than half moon most of the time. The planet attains its greatest western elongation on Sept. 3. Mars sets at 20h. 10m. and 18h. 50m. at the beginning and end of the month, respectively, and is too close to the sun for favourable observation. Jupiter can be seen for some time after sunset, the times of setting being 22h. 25m. and 20h. 40m. on Sept. 1 and 30, respectively, but the planet lies rather low for good observation in northern latitudes. Saturn rises at 4h. 10m. and 2h. 35m. at the beginning and end of the month, respectively, and can be seen as a morning star, stellar magnitude 0·9. One occupation of stars brighter than magnitude 6 occurs as follows : Sept. 27d. Olh. 43·5m., 47 Gemi. (R), where R refers to reappearance ; the latitude of Greenwich is assumed. Autumnal equinox commences on Sept. 23d. 03h.

The Night Sky in August

Full moon occurs on August 2d. 01h. 50m. u.t. and new moon on August 16d. 11h. 12m. The following conjunctions with the moon take place: August 12d. 22h., Mars.2° S.; August 15d. 10h., Mercury 4° S.; August 22d. 18h., Jupiter 0·1° N. In addition to these conjunctions with the moon, Mercury is in conjunction with Jupiter on August 18d. 13h., Mercury being 0·6° N. Mercury rises 1h. 22m. before the sun on August 1, but will not be an easy object to observe. It attains its greatest western elongation on August 3, and at the end of the month is a morning star, rising only 10 minutes before the sun. Venus rises 50 minutes before the sun on August 1 and practically at sunrise on August 31, and will not be well placed for observation during the month. Mars, in Gemini, is visible in the early morning hours, rising soon after midnight during most of the month. Jupiter, in the constellation of Libra, is visible in the early portion of the night, setting at 23h. and 21h. 06m. at the beginning and end of the month, respectively. Saturn, in conjunction with the sun on August 5, cannot be seen. The following occultations of stars brighter than magnitude 6 take place: August 14d. 03h. 21·5m., A Gemi. (R); August 24d. 20h. 29·0m., 88 B Ophi. (D). R and D refer to reappearance and disappearance, respectively, and the latitude of Greenwich is assumed. The Perseid shower of meteors attains its maximum about August 10–12; the radiant is close to R.A. 3h., Dec. + 57°.

The Night Sky in July

FULL moon occurs on July 14d. 09h. 22m. U.T. and new moon on July 28d. 11h. 53m. The following conjunctions with the moon take place: July 1d. 19h., Venus 3° S. ; July 3d. 07h., Mars 4° S. ; July 6d. 11h., Jupiter 4° S. ; July 31d. 15h., Venus 5° S. ; July 31d. 23h., Mars 5° S. Occultations of stars brighter than magnitude 6 are as follows, in the latitude of Greenwich: July 7d. 20h. 37.3s., x Virg. (D); July l1d. 21h. 19.5m., b Ophi. (D); July 18d. 0lh. 17.lm., 69 Aquar. (R). Mercury can be seen in the western sky in the early portion of the month, but later on it is too close to the sun for favourable observation. The planet attains its greatest western elongation on July 5 and is stationary on July 19. Venus sets at 22h. 16m. and 21h. 15m. at the beginning and end of the month respectively, and is conspicuous in the western sky. The stellar magnitude of the planet is -3.5 in the earlier portion, and -3.6 in the later portion, of the month. Mars sets 2½ hours after the sun on July 1, but at the end of the month only 1½ hours after the sun and is not well placed for observation in the latter case. Jupiter, near 0 Virgin is, sets at midnight on July 1 and about 1½ hours after the sun on July 31. The stellar magnitude of the planet varies from - 1.7 to - 1.5 during this period. Saturn is drawing in too close to the sun for favourable observation. The earth reaches aphelion on July 3d.

ASPECT OF THE HEAVENS FOR NOVEMBER AND DECEMBER, 1945

Mercury, always low on the horizon, will be lower than usual in the November twilight. This elusive planet may possibly be seen after sunset a few days before and after November 17, when it reaches its greatest eastern elongation of 22° 25 '. It will be in inferior conjunction with the sun on December 7. It will be stationary in R.A. on November 27 and again on December 16. Mercury may be seen in the morning sky just before sunrise a few daysbefore and after December 26, when the planet reaches its greatest western elongation of 22° 12'. Venus, with a magnitude of -3.4, will greatly outshine all other morning objects except the moon. On November 1, the planet rises just after Jupiter and about an hour and a half before the sun. Venus will quickly draw away from Jupiter toward the sun between November 1 and the end of December, moving from R.A. 13h lm and Deci. -4° 47' to 18h 5m and -23° 33'.

The Night Sky in October

FULL moon occurs oil October 13d. 13h. 23m. U.T., and new moon on October 27d. 15h. 23m. The following conjunctions with the moon take place: Oct. 18d. 04h., Mars 4° N. ; Oct. 18d. 14h., Saturn 2° N.; Oct. 23d. 07h., Jupiter 0-2° S. ; Oct. 25d. 03h., Venus 4° S. The following occultati ons of stars brighter than magnitude 6 take place: Oct. 3d. 18h. 01-Om., 49 Lib(D) ; Oct. 8d. 18h. 43.5m., 19 Cap(D); Oct. 15d. 02h. 59.2m., µ Cet(D); Oct. 15d. 04h. 10.3m., µ Cet(R); Oct. 15d. 22h. 17.4m., / Tau(D); Oct. 15d. 22h. 58.6m., / Tau(R); Oct. 17d. Olh. 26.5m., Y Tau(R). The times are given for Greenwich and D and R refer to disappearance and reappearance respectively. Mercury attains its greatest western elongation on Oct. 10. It is a morning star, and at the beginning of the month rises at 5h., an hour before sunrise. At the end of the month it rises at 6h. 15m., 35 minutes before sunrise. Venus is a morning star and rises at 3h. 17m. and 2h. 37m. at the beginning and end of the month respectively. The planet attains its greatest brilliancy on Oct. 13. Mars can be seen in the constellation of Taurus in the evening and sets at 12h. 32m. at the beginning of the month and at llh. 05m. at the end of the month. On Oct. 28 the planet is stationary. Jupiter, in the constellation of Leo, is a morning star, rising at Ih. 30m. at the beginning of the month and at midnight at the end of the month. Saturn can be seen close to Mars and is stationary on Oct. 9. At the beginning and end of the month the planet sets at 12h. 40m. and llh. 10m. respectively. Times are given approximately for the latitude of Greenwich. The Orionid meteor shower is due about Oct. 18-21. The radiant is close to the star v Orionis.

ASPECT OF THE HEAVENS FOR JANUARY AND FEBRUARY, 1943

The moon will be at perigee on January 6 and February 3 and at apogee on January 19 and February 16. Mercury. Mercury will be at eastern elongation on January 8, and may be seen in the sky just after sunset near that date. On January 24 it will pass between the earth and the sun, and will then move westward until it is at greatest western elongation on February 18. The best time to see Mercury during January and February will be just before sunrise for a few days preceding and following February 18. On January 7 and February 3, Mercury will be in conjunction with the moon. At the February conjunction it will be quite close to the new moon but too near the sun to be easily observed. Conjunction with Venus occurs on January 16. Venus. Venus will be a bright evening star quite close to the sun, 12° from it on January 1 and 39° on February 28. Conjunctions with the moon occur on January 7 and February 6, the one in February being a close approach, but the moon will have set for observers on the Pacific Coast at the time of conjunction. Mars. Mars will be an inconspicuous morning star, magnitude about 1.5, moving in the constellations of Ophiuchus and Sagittarius. During the year, Mars will become brighter and more conspicuous, its magnitude being -1.7 at opposition in December 1943.

The Night Sky in August

THE moon is new on August 15 at 3·9h. U.T. and full on August 29 at 22·lh. On August 25, ρ Sagittarii (magnitude 4·0) is occulted, the disappearance as seen from Greenwich taking place at 23h. 48·9m. at position angle 77° from the north point of the moon's disk. Conjunctions between moon and planets occur as follows: August 5d. 14h. with Jupiter; 7d. 9h. with Saturn; 26d. 14h. with Mars. On August 25 at 20h. Venus is in conjunction with Regulus, the geocentric distance between the planet and the star being 0·9°. Mars, Jupiter and Saturn rise in the evening, the respective times of southing on August 1 being 23h. 23m., 3h. 55m., and 5h. 20m.; by August 25 these times have changed to 21h. 35m., 2h. 17m. and 3h. 46m. Mars, a conspicuous object low in the evening sky, declines in brightness during the month from mag. — 2·5 to — 1·8; Jupiter increases slightly from mag. — 2·3 to — 2·4. Mercury reaches its greatest western elongation (18°) on August 28 and should be looked for in the early morning at about this date. Venus continues as a morning star rising in the dawn at 3h. 2Cm. on August 1 and at 4h. 38m. on August 25. Saturn reaches a stationary point on August 14, Mercury on August 20, Mars on August 24 and Uranus on August 28. The minor planet June is in opposition on August 19, when its magnitude is 8·3; on August 1 it is about 50′ south of α Aquarii. The Perseids reach their maximum frequency on or about August 9, their radiant point being near η Persei. In the late evenings of mid-August, with the moon absent, the region of the Milky Way near the southern meridian offers interesting ‘sweeps’ with binoculars or telescope.

The Night Sky in January

THE moon is full on January 5, and new on January 20. Lunar conjunctions with the planets occur as follows: on January 14 with Mars ; on January 16 with Venus ; on January 23 with Jupiter and with Saturn on January 26. Mercury, Venus and Mars are morning stars. Mercury is at greatest western elongation (23°) on January 3, and Venus reaches greatest western elongation (47°) on January 30. Venus rising shortly before 4Jh U.T. is pre-eminently the bright and morning star. Jupiter, southing in the early afternoon, is conspicuous in the evening sky. Saturn is due south shortly after 18h on January 1. The bright stars of the constellation of Orion and its associated constellations are passing the southern meridian about 22h in mid-January. The Quadrantids radiating from Draco may be looked for about January 2. On January 1, an occultation of the planet Uranus (mag. 6.0) takes place; at Greenwich the disappearance occurs at 17h0-lm at position angle 51° from the north point of the moon's image. On January 26, d Piseium (4-6m) is occulted at 17h l-2m, and on January 30, e Tauri (3-6m) at 19h 39-2m, the respective position angles at disappearance being 12° and 83° from the north point.

The Night Sky in June

ON June 21 at 20h, the sun enters the sign Cancer (the summer solstice). In the latitude of London, the length of night from sunset to sunrise is then only 7h 26m. The moon is new on June 8d 20-7h and full on June 23d 23-0h. On June 8, a total eclipse of the sun takes place and is visible in equatorial regions of the Pacific, but although the path of totality (of maximum breadth 153 miles) extends over nearly one hundred degrees of terrestrial longitude, there are very few possible land sites to which expeditions can be sent. The duration of totality at the noon point is 7m 4s, making this eclipse the longest that has occurred for more than a thousand years. Of the planets visible during June, both Mercury and Venus are morning stars. On June 6, Mercury is at greatest elongation 24° west, and Venus at greatest western elongation (46°) on June 27. Venus is in conjunction with Uranus on June 18 at llh, when the two planets are separated by 2-7°. Mars is conspicuous low in the south as the sky darkens. The planet decreases in brightness from magnitude 1-7 to 1-2 during the month. On June 20 at llh, Mars is in conjunction with the moon and is then only 0-1° northwards of the latter (geocentric positions). The circumstances produce an occultation of Mars by the moon, the phenomenon not, however, being visible from the northern hemisphere. Jupiter rises in the evening twilight and souths about 2h in the middle of the month; on June 25 at 2lh it is in conjunction with the moon. Saturn rises soon after midnight in mid-June; on June 4 at 2h conjunction occurs with the moon. The apparent breadth of the minor axis of the ring system is 3° 4′. At 22h in mid-June, the bright star Regulus is nearing the western horizon; Arcturus has passed the meridian, Sjr ica and Antares are low down in the south, while Vega, Altair and Deneb are conspicuous eastwards of the meridian. The maximum of the Scorpiid meteors is due about June 4, the radiant point being nearly midway between a Scorpii (Antares) and Y] Ophiuchi. An ephemeris for the comet Grigg-Skjellerup, is given in the B.A.A. Handbook as follows:

The Night Sky in February

BETWEEN February 1 and February 28, the length of the night in the latitude of London decreases from 14h 54m to 13h 13m. New moon occurs on February lld 7-6h and full moon on February 25d 7-7h. The planet Venus in the evening sky is a brilliant object; and in conjunction with the crescent moon on February 14d 2Sh will make a striking spectacle. On February 15 at 23h, the planet will pass within 3′ of the star 8 Piscium (magnitude 4.6). Venus is at greatest elongation (47° E.) on February 5. Mercury is a morning star at greatest western elongation (26°) on February 7, when it rises about lh 12m before the sun. On February 9 at 7h, Mercury is in conjunction with the moon, the planet being 2° south of the latter. In mid-February, Saturn sets about two hours after the sun. On February 20, the plane of the rings passes through the earth, and the appearance of the ring system in large telescopes will be of special interest. In 1920 and 1921 when the system could be viewed in similar circumstances as will occur on February 20, it was found that the rings did not completely disappear?a fact which has a bearing on their thickness and structure. On February 13 at 15h, Saturn will be in conjunction with the moon, the planet being 8° S. Jupiter rises near daybreak in the south-east; its magnitude is—1.5. The most favourable times for observing the light changes of Algol (R.A. 3h 04m, Dec. 40° 43′N.) are as follows: February 2d 2-4h, 4d 23-2h, 71 20.0h, 22d 4-1h, 25d 0-9h and 27d 21.8h. The radiant for the a Leonid meteors on February 22-28 is at R.A. 10-4h, Dec. 14° N.

Magnetic Influence of the Planets3

AN attempt to discover a direct magnetic influence emanating from the planets is described in “Magnetismus der Planeten,” by Ernst Leyst. For this purpose the author makes use of the observations taken at St. Petersburg and Pawlowsk during the years 1873–1889, and calculates the average magnetic declination for the days at which the planets are at their greatest and least distance from the earth; also for those days at which the planets are at their greatest eastern and western elongation. The numbers so obtained show certain regularities, which are considered sufficiently marked to indicate a true effect of the planetary configurations. According to the tables given, the declination is increased by 0·2 minutes of arc when Venus is nearest, and is diminished by 0′·32 when it is furthest away. Mercury acts in the opposite direction, diminishing the declination by 0′·29 when it is nearest, and increasing it by 0′·20 when it is furthest. The backbone of an inquiry like this ought necessarily to be found in a careful discussion as to how far an accidental combination of figures could account for the apparent effect. The magnetic declination is subject to so many changes which to us seem accidental, that if we take a certain number out of the whole series of daily averages, they must necessarily show deviations. The whole question then turns on the discussion whether the effects found by Mr. Leyst are sufficiently large and regular to be considered as real. This part of the subject is, unfortunately, treated in an insufficient manner, and, for this reason, the author has not in my opinion made out his case.