Comparison

Back in Time vs Stars Units Sizes Objects

Price, ratings, monetisation and update history for both apps, side by side — with what reviewers say about each.

Head to head
About

Back in Time

Explore the history of the Universe, Earth, Life, and Civilization through an immersive, interactive journey. This app uses custom animations, timelines, and interesting facts to bring historical events to life. It's designed to help users understand the connections between events and see the bigger picture.

Highlights
  • Interactive timeline of events
  • Custom animations and videos
  • Over 350 remarkable images
  • Little-known interesting facts
  • Offline access
  • Multilingual support
Features
Read full description

• "The coolest history textbook you’ll find on the iPad" - The New York Times • Winner of the WSA Mobile Award • Top1 iPad Book in US, UK, FR, ES, China… and 34 more Countries • Featured by The New York Times (Top10 iPad Apps of the year) • Featured by the American Photo Magazine (Top 10 Photo eBooks of the year) For iPhone/iPod touch download - Back in Time for iPhone Back in Time will take you on a stunning exploration of the history of our Universe, Earth, Life and Civilization. A journey through time where each event is documented with social and historical context, several images, an illustrative timeline and little-known interesting facts. Custom made animations bring those events to life, creating an interesting, immersive learning experience. An imaginary clock will guide you through this quest, proposing a simple analogy: the entire Universe started 24 hours ago. The Big Bang, the source of time and space, is the first event in our journey – the clock reads 0:00 hours. Today, 13.7 billion years later, the clock reads midnight. In between is a sequence of key events that has brought us to where we are today. Explore them, place them in perspective, see how they relate and understand the connections. We invite you to take a step back and see the whole picture. :::: REVIEWS :::: “...a beautifully executed lesson on the history of the universe and the evolution of life on earth. Great for high school students or parents who’d like to tutor younger children and enjoy a first-rate experience of their own...” - Bob Tedeschi, The New York Times “The iPad could use more apps like this one.” - The Daily “...the best iPad apps are those that combine coffee table-styled books with the fluid nature of the iPad’s interface. Back in Time is just that, it’s the story of the entire history of our universe made interactive on the iPad.” - Casey Chan, Gizmodo (App of the Day) “Back in Time is utterly gorgeous in its presentation. (...) The app is so easy to navigate that it is a delight to explore. Landka could scarcely have done a better job in putting everything together.” - Gwen Phua, Appmodo :::: FEATURES :::: Designed for iPad; 47 chapters; Over 350 remarkable images; 60+ amazing animations and videos; 40+ illustrated timelines; More than 200 little-known interesting facts; Music by the composer Rodrigo Leão; Developed in 7 different languages (English, Spanish, German, French, Portuguese, Japanese and Chinese); No internet connection required.

About

Stars Units Sizes Objects

Explore the vastness of the universe, from the smallest particles to the largest cosmic structures. Compare object sizes, view detailed images, and perform unit conversions across a wide range of astronomical scales. Learn about stars, galaxies, and the incredible distances between them.

Highlights
  • Compare object sizes
  • View object images
  • Pinch/Zoom and Pan images
  • Unit conversion for distances
  • Explore scales from Planck length to observable universe
  • Learn about stars and galaxies
Features
Read full description

Size of the smallest to largest objects and stars. Compare the size of objects in the universe. Object images. Pinch/Zoom image. Pan/Move image. Rotate image. Double tap to reset an image. From the smallest to the largest one. From planck length to observable universe. From Yoctometre, Zeptometre, Attometre, Femtometre, Picometre, Nanometre, Micro, Millimetre, Centimetre, Metre, KiloMetre, Lightyear, Parsecs, Billion Lightyears to 93 Billion Lightyears. Size of objects, particles, atoms, cells, stars and galaxies. Get to know the stars. Get to know the spaces. get to know the universe. How small is this world. How big is the universe. And How great is the creator. How far is the star distance from earth. Two way 18 distance unit conversion. planck length, yoctometer, zeptometer, attometer, femtometer, picometre, nanometre, micrometre, Millimeter, Centimeter, Meter, Kilometer, Inch, Foot, Mile, Astronomical, Lightyear, Parsecs. Perform auto conversion when picker is changed. Share conversion result. Reset unit convertor.

Screenshots

Stars Units Sizes Objects4 screens

Verdict

The call

The clearest difference is price: Stars Units Sizes Objects at Free against Back in Time's $7.99. Stars Units Sizes Objects also leads on device support (3 vs 1) and iOS requirement (11.0 vs 16.0). Back in Time's advantage is ads (none vs shown) and rating (4.6 vs 4.2). On review sentiment, update cadence and in-app purchases there is nothing between them.

Scored on Price · Rating · Positive reviews · Number of ratings · Update frequency · Ads · In-app purchases · Monetization · Best chart rank · Devices · Requires iOS

CostPrice · In-app purchases · Ads · Monetization

Stars Units Sizes Objects is free to download; Back in Time costs $7.99 up front. Neither carries in-app purchases, so what you see is what you pay.

ReceptionRating · Positive reviews · Number of ratings

Back in Time holds the better App Store score, 4.6 against 4.2. That said, the two scores are not equally well evidenced: Back in Time has 25 ratings behind it against 5, so its average is the more settled of the two. Written reviews point the same way: 84% of Back in Time's written reviews are positive against 80% of Stars Units Sizes Objects's.

UpkeepUpdate frequency

Back in Time ships an update every 7 months, Stars Units Sizes Objects every 4 months. The most recent releases landed on October 7, 2026 and September 22, 2026 respectively.

Scorecard7 real differences · 3 level
Back in Time versus Stars Units Sizes Objects: the parameters behind the verdict, then further details
ParameterBack in TimeStars Units Sizes Objects
Price$7.99Free — better
Rating4.6 (25 ratings) — better4.2 (5 ratings)
Positive reviews83.7% of reviews — better80.0% of reviews
Number of ratings25 — better5
Update frequencyEvery 7 monthsEvery 4 months — better
AdsNo — betterYes
In-app purchasesNoNo
MonetizationPaidAd-supported — better
DevicesiPadiPhone, iPad, iPod — better
Requires iOS16.011.0 — better
Further details — not scored
Size836 MB124 MB
Age rating4+4+
DeveloperLandkaMudarmeen Munlin

Customer experience

Back in Time

All ratings25 ratings
Positive92.0%
Neutral4.0%
Negative4.0%
Written reviews43 reviews
Positive83.7%
Neutral7.0%
Negative9.3%

Stars Units Sizes Objects

All ratings3 ratings
Positive100.0%
Neutral0.0%
Negative0.0%
Written reviews5 reviews
Positive80.0%
Neutral0.0%
Negative20.0%

In-app purchases

None

Back in Time

No in-app purchases

None

Stars Units Sizes Objects

No in-app purchases

Questions

Is Back in Time free?
Back in Time costs $7.99, with no in-app purchases.
Is Stars Units Sizes Objects free?
Stars Units Sizes Objects is free to download, with no in-app purchases.
Which has better reviews, Back in Time or Stars Units Sizes Objects?
Back in Time is rated higher. Back in Time averages 4.6 out of 5 from 25 ratings, while Stars Units Sizes Objects averages 4.2 from 5 ratings.
Do Back in Time or Stars Units Sizes Objects have ads?
Stars Units Sizes Objects shows ads; Back in Time does not.
Which is updated more often, Back in Time or Stars Units Sizes Objects?
Back in Time ships an update every 7 months, and Stars Units Sizes Objects every 4 months. Most recently, Back in Time was updated on October 7, 2026 and Stars Units Sizes Objects on September 22, 2026.

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