The top sights to observe or image this month
DON’T MISS: Comets C/2019 L3 Atlas and 19P/Borrelly
BEST TIME TO SEE: 1-4 February and 19-28 February
RECOMMENDED EQUIPMENT: Binoculars or Small/medium telescope
Last month, Comet C/2019 L3 Atlas reached perihelion in Gemini, when it appeared at its brightest, hovering about 10th magnitude. This month, L3 Atlas continues to be well positioned for UK viewing and, if it behaves as predicted, will remain around 10th magnitude, making it an object for larger binoculars and small telescopes.
Discovered by the ATLAS (Asteroid Terrestrial-impact Last Alert System) facility at Haleakala, Hawaii on 10 June 2019, the comet has been a steady performer for many months. It begins its February track 2˚ north of mag. +3.0 Mebsuta (Epsilon (ε) Geminorum). From here it tracks into the main shape of western Gemini, the Twins curving south to end the month 2˚ northeast of mag. +4.1 Nu (ν) Geminorum. This places it near the stars forming the foot of the twin Castor, which is a distinctive area thanks to the presence of open cluster M35. The cluster is located about 6˚ to the west-northwest of L3 Atlas at the end of February and a mid- or wide-field photograph should capture both objects easily.
C/2019 L3 Atlas isn’t the only reasonably bright comet visible this month. Comet 19P/Borrelly heads northeast through Pisces, the Fishes and into Aries, the Ram in February. 19P/Borrelly reaches perihelion on 2 February, and from the middle of January to 4 February it is expected to appear at mag. +8.0, making it a good target for binoculars and small telescopes.
The comet has been moving northeast and this month it will be favourably located. At February’s start, it’s positioned south of the narrowing pattern of stars converging on Alrescha (Alpha (α) Piscium). Use mag. +4.9 Mu (μ) Piscium and +4.4 Nu (ν) Piscium to locate it. 19P/Borrelly then tracks northeast, passing Mu Piscium by 0.6˚ on the evening of the 3rd and missing mag. +4.3 Omicron (ο) Piscium by 0.5˚ on the evenings of the 7th and 8th.
The comet slips across the border of Pisces and Aries on the 9/10 February, and on the evening of the 21st it appears 5˚ northwest of Uranus. As it continues tracking northeast, it ends the month close to mag. +5.5 Nu (ν) Arietis. At this time 19P/Borrelly lies 7˚ north of Uranus.
19P/Borrelly should appear brightest at February’s start, at mag. +7.9. By mid-month it’s predicted to be mag. +8.1, and it will be down to mag. +8.5 by the month’s close. Despite its slow decline, these magnitudes are still respectable for a comet and 19P/Borrelly should remain a decent binocular target for the month.
Catch the Lunar X and V
BEST TIME TO SEE: Early evening, 8 February
RECOMMENDED EQUIPMENT: Small/medium telescope
The Lunar X and V are popular light and shadow effects, visible close to when the Moon reaches first quarter. They belong to a growing list of clair-obscur effects; light and shadow arrangements that appear like familiar, everyday things.
Clair-obscur effects can last for several days or, as is the case here, just a few short hours. The Lunar X and V take on the appearance of the letters X and V, glowing within the lunar terminator shadow. Best seen through a small scope, they are formed when the lunar dawn’s light hits elevated features, while the lower-level terrain remains in darkness.
The Lunar V is formed when elevated ridges near the 23km crater Ukert become illuminated. The arms of the V are a bit ragged, but the effect is convincing at low magnification. The Lunar X is more complex, being formed when portions of the rims of three intersecting craters (68km La Caille, 118km Purbach and 68km Blanchinus) are illuminated.
In order to see clair-obscur effects, it’s necessary for the Moon’s terminator (the line between lunar day and night) to be in a precise position on the lunar surface, the Moon to be above the horizon and for clouds to be absent. In practice, having all three synchronise together isn’t as straightforward as you might imagine!
The Lunar X and V can be seen forming just after sunset on 8 February; the effect is at its best around 17:52 UT. Use a low magnification to start and look for the X one-quarter up the terminator from the southern edge. The V appears just north of the Moon’s centre on the 8th.
Morning planets: Mars and Venus
BEST TIME TO SEE: All month
RECOMMENDED EQUIPMENT: Naked eye
Venus and Mars are visible in the morning sky, not that well placed as seen from the UK as they are in the southern constellation of Sagittarius, the Archer. They form a mismatched couple during the month, Venus shining brightly at mag. –4.5, Mars much dimmer at mag. +1.4. However, they are interesting to watch if you have a flat southeast horizon as they appear to approach one another during the month.
On the 14th, Venus sits 6.5˚ to the north of Mars, the pair both above the horizon, 90 minutes prior to sunrise. Venus should be obvious, but you’ll probably have to wait a little longer for Mars to rise sufficiently to be visible through the low horizon murk. On the 14th, mag. +0.1 Mercury will also be there, forming the sharp point of a sunwardpointing isosceles triangle with Mars and Venus as the base.
A 15%-lit waning crescent Moon sits 4.7˚ south of Mars on the 27th. On this date, Mars and Venus will appear separated by 5.3˚, the Red Planet having brightened to mag. +1.3. By the month’s end, both planets appear 5.1˚ apart, with the separation dropping to just below 4˚ in the first half of March.