Portsmouth Stargazing & Astronomy Report

Key Sky Quality Metrics

SQM (mag/arcsec²)

18.88

Bortle class

Class 8 (Class 8)

Darkness Quotient

32%

Dataset

May 2026

City sky

Portsmouth: The Practical Verdict

Portsmouth, a small city in the United Kingdom, grapples with high light pollution which results in a rather disappointing experience for stargazing enthusiasts. The sky is dominated by urban brightness that eclipses the Milky Way entirely. The only observations that pierce this bright canopy are the Moon, planets, and a few bright stars.

The Milky Way remains completely invisible from Portsmouth due to the overwhelming city light. Observers will find the best success with brighter targets such as the Moon and planets. Challenges are significant for those hoping to observe deep-sky objects, with only narrowband imaging offering limited hope under careful conditions.

While local options offer some improvement, they are not dramatically darker. The best nearby site 17 km east-south-east offers Bortle class 5 skies, but the upgrade in darkness is still not profound, serving primarily as a step up for local observers.

At a Glance

Overall

Poor city sky - This is a poor city sky. The Milky Way is not visible and most deep-sky observing is unrealistic from the location itself.

Milky Way

Not visible - The Milky Way is erased by the bright urban sky background.

Best targets from here

Moon, planets, bright stars, double stars, solar system events, narrowband imaging only with care

Do not prioritise

visual deep-sky observing, broadband galaxies, reflection nebulae, widefield Milky Way

Limited nearby upgrade

17 km ESE is the strongest nearby option but remains Bortle 5; the improvement is real but modest.

Moderate dark window

Portsmouth's longest dark windows fall in December and January, with the shortest nights around June and July. Plan deep-sky sessions around the autumn and winter months for the best combination of long nights and true astronomical darkness.

Frequently Asked Questions

Can you see the Milky Way from Portsmouth?

No. Portsmouth is a Bortle Class 8 sky with SQM 18.88, so the Milky Way is not visible from the city. For Milky Way photography, look for a Bortle 4 or darker site.

What Bortle class is Portsmouth?

Portsmouth is Bortle Class 8 (SQM 18.88), a poor city sky for astronomy.

Is Portsmouth good for stargazing?

Not for serious deep-sky observing. Portsmouth is a poor city sky where the Moon, planets, and a handful of bright targets are the realistic options from the city itself.

Is Portsmouth good for astrophotography?

Broadband deep-sky imaging is heavily compromised from Portsmouth and a Bortle 4 or darker site is strongly recommended. Even narrowband imaging is difficult from Portsmouth without careful processing.

What can you observe from Portsmouth?

Primary targets from Portsmouth include Moon, planets, bright stars, double stars, solar system events. Targets such as visual deep-sky observing, broadband galaxies, reflection nebulae are not realistic from this sky.

Where are darker skies near Portsmouth?

The closest meaningfully darker mapped site is 17 km ESE, about 17 km east south east of Portsmouth, reaching Bortle 5.

When is the sky darkest in Portsmouth?

The sky over Portsmouth is darkest around January, December. Significant summer limitation: around 52 nights per year have no true astronomical darkness.

Is light pollution in Portsmouth getting better or worse?

The long-term trend for Portsmouth is gradually improving, with the sky darkening by about 0.04 SQM per year.

• 17 km ESE

  Direction

  ESE

  Distance (km)

  17.4

  SQM

  20.62

  Bortle

  5

• 21 km SW

  Direction

  SW

  Distance (km)

  21.4

  SQM

  20.48

  Bortle

  5

• Froyle

  Direction

  N

  Distance (km)

  38.8

  SQM

  20.45

  Bortle

  5

• Litchfield and Woodcott

  Direction

  NNW

  Distance (km)

  54.7

  SQM

  20.40

  Bortle

  5

• 62 km WNW

  Direction

  WNW

  Distance (km)

  62.4

  SQM

  20.31

  Bortle

  5

• 81 km ENE

  Direction

  ENE

  Distance (km)

  80.8

  SQM

  20.45

  Bortle

  5