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Note: This page will feature The Orcadian’s monthly Look to the Sky column. Additional material may be added as appropriate.
Look to the Sky, 2017 Arpil: Jupiter at Opposition. PDF Version.
25 Mar 2017 13:51:15 Venus observed 03h 34m following inferior conjunction.
Right ascension: 0h 4m 33.31s
Declination: +9° 31' 11.9"
Altitude: 36° 9' 19"
Azimuth: 214° 38' 25"
True distance from Earth: 0.2810908 AU (42 million km) Light time: 0h 2m 20.3s
25 Mar 2017 13:51:15 Venus observed 03h 34m following inferior conjunction. 100mm apochromatic refractor 260x a 1/1000 sec. exp. Canon IXUS 310HS ISO 100.
Note: Mercury, 18° east of Venus, was also imaged.
True distance from Earth: 1.0691909 AU (160 million km) Light time: 0h 8m 53.6s
2017 March 25: at 13h 51m UT 100mm apochromatic refractor 260x a 1/1000 sec. exp. Canon IXUS 310HS ISO 100.
Venus approaching Inferior Conjunction.
2017 March 22. Imaged 14h 00m UT 100mm apochromatic refractor. 1/1000 sec.
Look to the Sky March 2017 Extra: Venus at Inferior Conjunction March 25th
We mentioned in the regular Look to the Sky column for March that Venus would be retreating from our evening skies by the middle of the month. This will lead to the planet lining up with the Sun on March 25th, referred to as inferior conjunction. Then, the Earth, Venus and the Sun (in that order) will be inline, though not quite in the same plane. This means that on March 25th close to noon Venus will appear some 8 arc-degrees above the Sun in the sky (the Sun has an apparent diameter of 0.5°).
Due to Venus's superior northern declination over the Sun, Venus will rise before and set after the Sun in the period 23rd February to 28th March. The optimum days for seeing Venus in the morning and evening skies will be 23rd/24th March.
On the 25th Venus will rise a little north of East at 04h 55m, or 1h 4m before sunrise, setting 33 minutes after sunset, a little north of west, in the early evening. In common jargon, we could say Venus appears as both a morning star and an evening star on one and the same day. Evening viewing will offer the greater challenge to the naked eye observer and will require a good western horizon.
Those with small telescopes should have no problem following Venus into the morning, daytime sky. Indeed this will offer the best conditions for the observer since the bright sky background will provide suitable contrast for the brilliant planet. But under no account allow the Sun to enter the field of view of the telescope. Binoculars, with their wider field, should not be used with the planet this close to the Sun in the sky.
Venus at or close to inferior conjunction yields an apparent diameter of around 1 arc-minute (approximately 1/30th of the Moon's apparent diameter).
On March 25th Venus will be at a distance from Earth of 42 million km yielding a phase of exactly 1%. However, due to the planet's dense atmosphere sunlight is refracted around the full limb such as to yield an annular or ring-like effect when viewed through the telescope (see accompanying image).
Note: Instruments should be mounted on a suitable, firm mounting or tripod.
Both Mercury and Venus move in orbits within that of the Earth's orbit about the Sun, hence the term inferior planet. However, the two planets differ in some respects, most notably to the visual observer in their apparent brightness, relating to the planet's phase as seen from Earth. This will be discussed in some detail in the June, paper column.
We repeat, when observing close to the Sun in the sky extreme caution needs to be exercised so as not to view the Sun itself direct.
The next comparable conjunction will take place in 2025. March 23rd.
Venus approaching inferior conjunction imaged with a 100mm aperture apochromatic refracting telescope 120x power at 15h 45m UT on June 3rd 2012.
Look to the Sky 2017 March: Equinoxes and More (PDF version).
Look to the Sky February 2017: Antares—the Summer Star in Our Winter Skies. PDF version avaialbe HERE.
2017 February 02, 06h 39m UT. Looking SSE with Saturn left Antatres right (above white lines). D300 SLR 24mm f/2.8 lens.
Look to the Sky January 2017: Venus and Mars in the evening sky
As mentioned last month, Venus will gain in prominence in the evening sky as the days pass seeming to draw ever closer to the fading Mars.
There will not be a better opportunity to follow the relative motions of our two closest planets as they appear to hover within some 5 arc-degrees of one another for some time in late January/early February, with the crescent Moon again to be seen between the two on January 2nd and 31st.
Both planets are moving rapidly (W to E) against the star background, as represented in the diagram commencing January 1st at 17h UT. Mars's angular movement 1st to 31st Jan. is 22°; Venus's angular movement for the same period will be 30°, both rounded up to the nearest arc-degree.
The diagram shows the sky looking SSW at 17h (5 pm) on January 1st. The lines to the left of each planet indicate the movement against the star background over 4 days. The Moon, with an apparent diameter close to 0.5°, appears to move W to E at approximately 13° in 24 hours, and will be well east of the planets by the 4th January.
Mars will be a little below the red, variable star lamda Aquarii (mag. 3.7) on the 3rd.
As featured in the December 2016 Look to the Sky, Venus was low down in constellation Sagittarius with Mars well to the east in Capricornus. Both planets will be seen to have made a marked increase in elevation by the middle of January, with Mars moving out of constellation Aquarius into Pisces on the 19th, followed by Venus four days later.
Venus, however, is moving in its orbit so as to approach the Earth, resulting in a rapid change in appearance from a phase of 56.3% on the 1st to 39.8% on the 31st. Within this period there will be a significant increase in apparent angular diameter to 30.76".
Those with small telescopes should have no difficulty following these changes in appearance of our nearest planet. However, it is strongly recommended to observe in strong twilight in order to reduce the contrast between sky and the brilliant Venus.
Venus moves in space swiftly towards us, so as to be at inferior conjunction on March 23rd, meaning it will have disappeared from the evening sky by early March. Mars, on the other hand, is moving away from Earth and will linger in the evening sky up to early May.
The evening twilight by the end of January will be giving rise to the phrase "the evenings are dawning out". This encroachment of twilight into the night sky gathers pace both in the evenings and before dawn as we move towards the vernal equinox. This we will feature in detail in the March column.
Planet Jupiter is now conspicuous in the SE skies in the early hours, rising at 01h 32m UT on the 1st January and at 23h 42m UT on the 31st. The planet will appear above the bright, 1st magnitude star Spica (a Virginis) and will have the company of the Moon (phase 58%) on the morning of the 19th January.
Phases of the Moon:
First quarter: 05 Jan.19h 47m
Full moon: 12 Jan.11h 34m
Last quarter: 19 Jan. 22h 13m
New moon: 28-Jan. 00h 07m
Looking a little west of south on 2017 January 1st at 17h (5pm) UT.
Additions: Venus Mars & Neptune (between short, white lines) imaged 2016 December 19 at 17h 23m UT. An 8 sec. exposure 28mm f/2.8 Nikkor, D100 ISO 600. Static camera. (Click on image to enlarge.)
Note: Orange glow from Rousay Jetty region.