ISO 2026-W04

ISO 2026-W04 runs from January 19 through January 25. Mercury and Mars are separated by about 0.6° in geocentric ecliptic longitude at the Monday 00:00 UTC snapshot. Venus and Pluto are separated by about 1.4° in geocentric ecliptic longitude at the Monday 00:00 UTC snapshot.

Naked eye: No principal lunar phase is listed this week. Check the Moon's position each night and favor darker hours for low-contrast targets. Use Cursa, Rigel, Capella, Bellatrix, Elnath, Nihal as the week’s fixed-sky framework.

Cursa — the footstool beside Orion points to a hidden bat — Cursa stands at the northern beginning of Eridanus, bright enough to see easily and close enough to guide a telescope to the much fainter reflection nebula NGC 1788.

Rigel — a blue supergiant that refuses to stand still — Rigel fixes one brilliant corner of Orion, but the apparent point is a swollen, wind-losing supergiant whose light and spectral lines pulse on many different clocks.

Capella — one winter beacon, two evolving giants — Capella looks like a single golden point, but precision orbits separate its light into two giant stars of nearly equal mass caught in very different, rapidly changing evolutionary stages.

Bellatrix — the warrior who did not lead a cluster — Bellatrix appears to stand among Orion's bright family, and it once seemed well placed to lend its name to a nearby young stellar group. Precise motion across space overturned that attractive association.

Elnath — the shared horn with a peculiar atmosphere — Elnath marks the northern horn of Taurus and a corner of Auriga's familiar outline. Its hot atmosphere also carries the uneven chemical fingerprints of a mercury–manganese star—although one famous mercury line is missing.

Nihal — a nearby giant balanced between two labels — Nihal is a yellow evolved star in the body of Lepus. Its spectrum sits near the border between giant and bright giant, a useful reminder that stellar classifications summarize evidence rather than draw hard physical walls.

Planets: Moon: In solar glare; magnitude -4.3; direct motion; 0.1% illuminated. Monday 00:00 UTC snapshot. Conjunction with Venus in ecliptic longitude Jan 19 02:02 UTC. Conjunction with Ceres in ecliptic longitude Jan 24 12:33 UTC. Conjunction with Saturn in ecliptic longitude Jan 23 09:32 UTC. Conjunction with Neptune in ecliptic longitude Jan 23 13:17 UTC. Conjunction with Pluto in ecliptic longitude Jan 19 04:35 UTC. Mercury: In solar glare; magnitude -1.2; direct motion; 99.7% illuminated. Monday 00:00 UTC snapshot. Solar conjunction in ecliptic longitude Jan 21 15:49 UTC. Conjunction with Pluto in ecliptic longitude Jan 22 17:14 UTC. Venus: In solar glare; magnitude -3.9; direct motion; 99.9% illuminated. Monday 00:00 UTC snapshot. Conjunction with Moon in ecliptic longitude Jan 19 02:02 UTC. Conjunction with Pluto in ecliptic longitude Jan 20 04:04 UTC. Mars: In solar glare; magnitude 1.1; direct motion; 100.0% illuminated. Monday 00:00 UTC snapshot. Ceres: Telescope; magnitude 9.0; direct motion; 97.3% illuminated. Monday 00:00 UTC snapshot. Conjunction with Moon in ecliptic longitude Jan 24 12:33 UTC. Jupiter: Naked eye; magnitude -2.7; retrograde motion; 100.0% illuminated. Monday 00:00 UTC snapshot. Saturn: Naked eye; magnitude 1.0; direct motion; 99.8% illuminated. Monday 00:00 UTC snapshot. Conjunction with Moon in ecliptic longitude Jan 23 09:32 UTC. Uranus: Binoculars; magnitude 5.7; retrograde motion; 100.0% illuminated. Monday 00:00 UTC snapshot. Neptune: Telescope; magnitude 7.8; direct motion; 100.0% illuminated. Monday 00:00 UTC snapshot. Conjunction with Moon in ecliptic longitude Jan 23 13:17 UTC. Pluto: In solar glare; magnitude 14.5; direct motion; 100.0% illuminated. Monday 00:00 UTC snapshot. Solar conjunction in ecliptic longitude Jan 23 10:28 UTC. Conjunction with Moon in ecliptic longitude Jan 19 04:35 UTC. Conjunction with Mercury in ecliptic longitude Jan 22 17:14 UTC. Conjunction with Venus in ecliptic longitude Jan 20 04:04 UTC.

Binoculars: Trace Mensa’s charted figure in the finder, then identify β Men at its charted position. Trace Camelopardalis’s charted figure in the finder, then identify β Cam at its charted position.

Beta Mensae — a distant giant over Table Mountain — The Greek letter suggests a prominent marker, but Beta Mensae is a fifth-magnitude giant in one of the faintest southern constellations—a useful reminder that a Bayer letter is a label, not a ranking guaranteed by the modern sky.

Beta Camelopardalis — a supergiant measured across a milliarcsecond — Beta Camelopardalis looks like a quiet fourth-magnitude point, yet interferometry has resolved its apparent diameter: several telescopes can combine their light to measure a star no single backyard view can turn into a disk.

Small telescope: vdB 33: consult its dedicated finder and observing story for equipment guidance; NGC 1851: consult its dedicated finder and observing story for equipment guidance; Flaming Star Nebula: consult its dedicated finder and observing story for equipment guidance; M79: consult its dedicated finder and observing story for equipment guidance; M38: consult its dedicated finder and observing story for equipment guidance; NGC 1931: consult its dedicated finder and observing story for equipment guidance

NGC 1788 — the Cosmic Bat reflects a changing nursery — NGC 1788 does not manufacture most of the light that draws its wings. Dust scatters starlight from a young cluster, while a red rim and an age sequence preserve evidence—still interpreted cautiously—of star formation pushed outward from Orion.

NGC 1851 — one globular cluster, more than one stellar history — NGC 1851 looks like one compact swarm, but its colour–magnitude diagram and chemistry divide the stars into distinct populations. The cluster is old; its history is not simple.

IC 405 — a runaway star lights a borrowed flame — The Flaming Star Nebula is not a stellar birthplace neatly surrounding its native sun. AE Aurigae crossed into the cloud after a violent ejection elsewhere, and its ultraviolet light now makes gas emit while dust reflects.

M79 — an old cluster whose young-looking stars sank inward — Messier 79 is an ancient stellar city, yet its centre contains blue stragglers that look younger than their neighbours. Their concentration records the long action of gravity inside the cluster.

M38 — a broad main sequence without a second chemistry — M38 looks like a loose spray of Auriga stars. Precise Gaia measurements reveal a broadened lower main sequence, but a careful multicolour test finds that dust and unresolved binaries can explain it without inventing a second stellar recipe.

NGC 1931 — a young cluster seen through unusual dust — NGC 1931 is a compact nursery where newborn stars share the eyepiece with glowing and reflecting dust. Measurements show that its dust dims and reddens starlight differently from the diffuse material usually assumed in textbook corrections.

Substantial telescope: No fixed-sky Calendar object is classified as requiring a substantial telescope this week.