Characteristics of Stars - Free Printable

Let's solve each part of this worksheet step by step.

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Problem 1: Organize the pictures on the timeline based on surface temperature

We are given four images of stars, and we need to arrange them from coolest (left) to hottest (right) based on their surface temperature, which can be inferred from their color.

#### Color-Temperature Relationship:
- Red → Coolest
- Orange/Yellow → Moderate
- White → Hot
- Blue → Hottest

Now let’s analyze the images:

1. First image (yellow-orange) – This is similar to the Sun, so it's a medium-temperature star.
2. Second image (white) – White stars are hotter than yellow ones.
3. Third image (red) – Red stars are the coolest.
4. Fourth image (blue) – Blue stars are the hottest.

So, ordering from coolest to hottest:

1. Red (third image)
2. Yellow-orange (first image)
3. White (second image)
4. Blue (fourth image)

#### Final arrangement on the timeline:
```
[Red] ——— [Yellow-orange] ——— [White] ——— [Blue]
coolest hottest
```

> ✔ So, place the images in this order on the timeline.

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Problem 2: Rank the brightness of stars when viewed from Earth

We are to rank the stars from dimmest (1) to brightest (5) based on distance from Earth.

Important concept:
Apparent brightness (how bright a star looks from Earth) depends on both its intrinsic brightness and distance. But since we don’t have intrinsic luminosity data, we assume all stars have similar luminosity for comparison purposes. Therefore, closer stars appear brighter.

So, brightness ∝ 1 / distance² (inverse square law), but since we're just ranking, we can use distance alone:
→ The closer the star, the brighter it appears.

Let’s list the distances:

| Star Name | Distance from Earth |
|-------------------|------------------------------|
| Barnard's Star | 5.96 light-years |
| Alpha Centauri | 4.37 light-years |
| The Sun | 150 km (≈ 0.0000158 light-years) |
| Sirius | 8.58 light-years |
| Ross 154 | 9.68 light-years |

Now, convert all to comparable units. Since 150 km is extremely close compared to light-years, the Sun is by far the closest.

Let’s rank by distance (closest = brightest):

1. The Sun – 150 km away → Closest → Brightest
2. Alpha Centauri – 4.37 ly
3. Barnard's Star – 5.96 ly
4. Sirius – 8.58 ly
5. Ross 154 – 9.68 ly → Farthest → Dimmest

But wait: Sirius is actually one of the brightest stars in the sky, even though it's farther than some others, because it is intrinsically very bright.

However, the problem says:
> "Use the distances of the stars to rank their brightness"

This implies we should assume equal intrinsic brightness and only consider distance.

So under that assumption:

- Closer = brighter
- Farther = dimmer

Thus, ranking from dimmest (1) to brightest (5):

| Star Name | Distance | Rank (Brightness) |
|-------------------|------------------|--------------------|
| Ross 154 | 9.68 ly | 1 (dimmest) |
| Sirius | 8.58 ly | 2 |
| Barnard's Star | 5.96 ly | 3 |
| Alpha Centauri | 4.37 ly | 4 |
| The Sun | 150 km (~0 ly) | 5 (brightest) |

✔ So fill in the table:

| Star Name | Distance From Earth | Brightness |
|-------------------|----------------------------|------------|
| Barnard's Star | 5.96 light-years away | 3 |
| Alpha Centauri | 4.37 light-years away | 4 |
| The Sun | 150 km away | 5 |
| Sirius | 8.58 light-years away | 2 |
| Ross 154 | 9.68 light-years away | 1 |

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✔ Final Answers:

#### 1. Timeline Order (coolest to hottest):
From left to right:
- Red star (coolest)
- Yellow-orange star
- White star
- Blue star (hottest)

#### 2. Brightness Ranking (1 = dimmest, 5 = brightest):

| Star Name | Brightness |
|-------------------|------------|
| Barnard's Star | 3 |
| Alpha Centauri | 4 |
| The Sun | 5 |
| Sirius | 2 |
| Ross 154 | 1 |

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🔍 Explanation Summary:

- Color indicates temperature: Red = cool, Blue = hot.
- Distance affects apparent brightness: Closer stars appear brighter (if intrinsic brightness is assumed equal).
- The Sun is extremely close, so it appears much brighter than any other star, even though it's not the most luminous.
- Sirius is intrinsically bright, but since we’re using only distance, it ranks lower than closer stars like Alpha Centauri.

Let me know if you want to explore actual luminosities!