# Citizen Sky View vs Mars Book

The clearest difference is update cadence: Citizen Sky View at every 2 weeks against Mars Book's every 13 months. On price, ads, in-app purchases and device support there is nothing between them.

Both are free to download. Neither carries in-app purchases, so what you see is what you pay.

Citizen Sky View ships an update every 2 weeks, Mars Book every 13 months. The most recent releases landed on October 9, 2026 and October 26, 2026 respectively.

## The numbers

| Metric | Citizen Sky View | Mars Book |
| --- | --- | --- |
| Price | Free | Free |
| Rating | **[5.0 (1 ratings)](https://appshunter.io/ios/app/citizen-sky-view/id1302449465/reviews)** | — |
| Number of ratings | **1** | — |
| In-app purchases | No | No |
| Ads | No | No |
| Update frequency | **Every 2 weeks** | Every 13 months |
| Monetization | Free | — |
| Size | 26 MB | 14 MB |
| Requires iOS | 10.3 | **9.0** |
| Devices | iPhone, iPad, iPod | iPhone, iPad, iPod |
| Age rating | 4+ | 4+ |
| Developer | [University of Colorado Boulder](https://appshunter.io/developer/972210292) | [Vixen Co.,Ltd.](https://appshunter.io/developer/536188843) |

## What reviewers say

### Citizen Sky View

[App page](https://appshunter.io/ios/app/citizen-sky-view/id1302449465)

Participate in a NASA-sponsored citizen science project to study cloud formation. Coordinate with the project team for events, then use your phone to capture images of the sky at assigned locations and times. Your contributions help researchers learn more about atmospheric science.

**Highlights:** Citizen science participation, Cloud formation research, Event coordination, Location-based image capture, Data contribution for research

**Features:** macOS Compatibility, Vision Pro support

**In-app purchases:** none


### Mars Book

[App page](https://appshunter.io/ios/app/mars-book/id1342509724)

**In-app purchases:** none


## Frequently asked questions

### Is Citizen Sky View free?

Citizen Sky View is free to download, with no in-app purchases.

### Is Mars Book free?

Mars Book is free to download, with no in-app purchases.

### Do Citizen Sky View or Mars Book have ads?

Neither Citizen Sky View nor Mars Book shows ads.

### Which is updated more often, Citizen Sky View or Mars Book?

Citizen Sky View ships an update every 2 weeks, and Mars Book every 13 months. Most recently, Citizen Sky View was updated on October 9, 2026 and Mars Book on October 26, 2026.

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*Compared by [AppsHunter](https://appshunter.io/) from daily US App Store data. Review summaries are generated from verbatim App Store reviews.*