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NASA’s September 28 skywatching guide identifies Algol as a target whose brightness dips on a roughly three-day cycle and describes two nebulae with Halloween-inspired names. The guide says Algol can be observed with the naked eye; the Witch Head Nebula is not visible to the naked eye and is a challenging target that may require dark skies, a large-aperture telescope or astrophotography.
NASA published an October skywatching guide on September 28, pointing autumn observers to Algol’s periodic dimming and two nebulae with Halloween-inspired names. The guide explains how to watch Algol change brightness and describes the Witch Head Nebula as a challenging target for visual observers.
NASA’s guide places Algol in Perseus and notes that it is also known as the Demon Star or the Ghoul. It says Algol appears in the northeastern sky during autumn, along with Cassiopeia and Andromeda, beginning after 9 p.m. The guide links the star’s name and its association with Medusa’s blinking eye to Greek mythology, and describes the observed change in brightness as an astronomical phenomenon.
According to NASA, Algol is a triple-star system, with two stars orbiting one another. As one passes in front of the other from Earth’s viewpoint, the system dims from about magnitude +2.1 to +3.4 roughly every three days. NASA includes a light curve made with data from the Transiting Exoplanet Survey Satellite, or TESS, to show the repeating dip. The guide suggests comparing Algol with nearby Almach, also called Gamma Andromedae, using binoculars or a small telescope.
The guide also describes IC 2118, the Witch Head Nebula, as a reflection nebula about 900 light-years away between Eridanus and Orion. NASA says the nearby star Rigel illuminates it and that it is not visible to the naked eye. The guide says large-aperture telescopes at low magnification may help under dark skies; astrophotographers may capture it over a few hours, depending on equipment and sky conditions. A third seasonal target, the Witch’s Broom, is part of the Western Veil Nebula in Cygnus.
A Seasonal Test for Skywatchers
NASA’s guide describes two observing approaches: tracking a repeating brightness change with unaided eyes and seeking faint nebulae that require more equipment or imaging. Algol’s brightness can be compared over several nights, while the guide says the Witch Head Nebula requires dark skies, a large telescope or astrophotography equipment.
The guide explains how eclipsing binary stars produce a change in apparent brightness. It says no specialized equipment is required to observe Algol’s change, though a comparison star and attention to timing can help observers follow the pattern. It also notes that nebulae shown in photographs may not appear clearly through ordinary binoculars or to the naked eye.
NASA links the guide to a separate article about sidewalk astronomy and Halloween, which offers ideas for public outreach. The October guide presents observing suggestions rather than a new mission result.
October Targets in the Autumn Sky
The guide, written by Kat Troche and published by NASA Science, describes objects visible or photographable during autumn. It places Algol in Perseus and says Cassiopeia and Andromeda can help orient observers in the northeastern sky after 9 p.m. NASA describes Algol’s dimming as recurring about every three days and references TESS data for the corresponding light curve.
NASA describes the two nebulae as seasonal targets. The Witch Head Nebula is a reflection nebula, meaning its visible glow comes from starlight reflected by nearby dust. The guide places it about 900 light-years away and identifies Rigel as the illuminating star. NASA identifies the Witch’s Broom as part of the Western Veil Nebula in Cygnus. The guide’s Halloween framing refers to the objects’ shapes and names.
Visibility Depends on Conditions
NASA’s guide provides approximate observing guidance, not a location-specific forecast or a night-by-night schedule. It does not specify how high each target will appear at different latitudes or give exact dates and times for Algol’s dimmest point in October. The guide advises consulting observing charts or other resources for local conditions and eclipse timing.
The guide says visibility of the Witch Head Nebula depends on sky darkness and equipment. It notes that large-aperture telescopes at low magnification can make it easier to catch and that imaging may take a few hours depending on equipment and sky quality. NASA does not say every observer will see or photograph it. The guide gives the nebula’s distance as about 900 light-years but does not provide further measurement details.
Plan Around Clear Autumn Nights
NASA suggests locating Perseus and comparing Algol’s brightness with Almach over several nights to look for the roughly three-day dimming cycle. The guide recommends using an interactive chart or data plot to calculate Algol’s minima, or faintest points, without naming a specific chart.
For the Witch Head Nebula, NASA recommends dark skies and suitable telescope or imaging equipment; the guide says photographers may need several hours and should account for local sky quality. It also links to NASA’s Trick or Treat: Sidewalk Astronomy article for community observing ideas. Local viewing conditions will affect which targets are practical on a given night.
Key Questions
What causes Algol to dim?
NASA describes Algol as a triple-star system in which two stars orbit one another. Their eclipses, as seen from Earth, cause the system’s apparent brightness to fall from about magnitude +2.1 to +3.4 roughly every three days.
Can I see Algol without a telescope?
NASA’s guide presents Algol as a star to observe in the autumn sky and suggests comparing its brightness with Almach using binoculars or a small telescope. The guide does not say that a telescope is required to watch the brightness change.
Can I see the Witch Head Nebula with my eyes?
No. NASA says the Witch Head Nebula is not visible to the naked eye. The guide says large-aperture telescopes under dark skies or astrophotography equipment offer better chances of observing or imaging it.
Where is the Witch’s Broom?
NASA identifies the Witch’s Broom as part of the Western Veil Nebula, located in the constellation Cygnus.
Source: primary
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